Origins of Flavour in Whiskies and a Revised Flavour Wheel ... · volatile congeners more...

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Origins of Flavour iu Wlliskies and a Rt>vised Flavour Wlteel: a Review, pp.287-313 Volume 107, No. 5, 2001

Origins of Flavour in Whiskies and a Revised Flavour Wheel: a Review By K.-Y. Monica Lee, Alistair Paterson* and John R. Piggott

Cent re for Food Quality, University of Strathclyde, Department of Bioscience, 204 George Street, Glasgow G11XW, Scotland, UK

and

Graeme D. Richardson

The Scotch Whisky Research lnstitute, Tlre Robertson Trust Building, Science Park North, Riccarton, Edinburgll EH14 4AP, Scotland, UK

Received 13 October 2000; revised version received and accepted 11 December 2000

The nature artd origins of flavour in wltiskies are reviewed witlr the aim of developing a revised and simpUfled flavour wheel for traitti~tg of senson; assessors. Scotch whiskies are perceived as having distinctive cltaracters, generally recognised in pattem recognition (perception, macroscopie bra in processing), rather than being subjected to a deconstruction process of evaluating attributes (sensation, microscopie brailt processing). Althougit consmners use simple recognition judgeme11ts on whisky flavour in categorical assimilation, i11dustnJ has a requirement for monitoring spirit quality that necessitates a more reductionist approach. Whisky flavour wheels identify attributes, specific components of flavour character, wltich ca11 be demonstrated to sensory assessors using reference standards. Tlze adveut of cyclodextrin bound reference standards has enabled commtmicatiott of ittfonnatiott otl flavour character in training of assessors, as exploited in tlte brewi11g industry. A revised flavour wheel, witlt clraracters illustrated by reference standards, is proposed to assist senson; trai11ing on attributes of whisky flavour character.

Key Words: Whisky jlavour character, whisky jlavour reference standards, jlavour perception and sensation, sensory assessor training, quality evaluation.

INTRODUCTION

Improvcd congener analyses have not yielded greater understanding of whisky flavour51: a dynamic interaction209 between individuals and flavour components268, Perceptions of flavour, notes or attributes can be expressed as language91,233 but are more commonly used in Gestalt65,91,I07,16J.232,242 or holistic pattem recognitions in human brains22t, perception of wlwle over parts (macroscopie brain processing) (Fig. I)10ï,242. In contrast, in industrial sensory assessments, quantified sensations are intcgratcd from specific groups of olfactory receptars (microscopie processing). Assessors can also agree on character while differing in quantities of mouth-space volatile flavour componentsl35.

In consumers, causality interactions ( slaving effects) exist between perceptual and sensation levels, dictated by cues117 (Fig. 1): thc human mind influences the brain242.

•corresponding author

Appreciation of whisky character is a synergistic and holistic perceptual process with extrinsic attributes (branding, labelling, marketing and packaging) important in choke dedsions (Fig. 1). A drink is more than the sum of its component perceptions. Sensory assessors genera te data relevant to consumer judgements, but utilise different forms of mental processing.

On tasting uniabelled whisky, consumers match perceptions against prior experience, using intrinsic attribute patterns. On a mismatch, individuals move to cvaluating small numbers of intrinsic attributes, dusters of individual assessments, with sequential creation of further mental images242. Such processing is modelled in sequentia! assessor evaluations of attributes in appearance, aroma, taste, mouthfeel and after-taste.

Psychophysics suggests humans have physiological limitations in perceptual ability23 and can identify no more than three or four flavours notes in mixtures119,120,122. Only this number are held in short-term memory, more

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Volume 107, No. 5, 2001 Origins of Flavour in Whiskies m1d a Revised Flavour Wlleel: a Revit•w

INTRINSIC ATTR1Bl'TES CENTRAL

INTEGRATION ~• ACTION

Appearwu:e. Aroma. Taste. .\/outh{t•el.

EXTRlSSIC ATTRIBUTES

. -1/ ll'l"l W I,,

I:\ peetaf ion . Experh·m:e . /Jrcmd Image. Packaging . . \ /urkl'l ing. Prin•

t IT.tll.u -.Uh;IIU\ llllfl;tdiPil .\ót.mthm \ t il:ros~:opic lè\ èl

~ .. L\I.i\,i,.~;:,;,::Îi .. ,..

FIG. 1. Tntrinsic and extrinsic attributcs.

in long-term memorym. Spatial response pattems of flavour component mixtures may thus nol be summations of individual flavour notes123.

The beer flavour wheels125.t57 concentrale assessor attention to specific flavour attributes, induding mouthfeel attributes, important in beer. Studies of wood-matured ports52 and whisky21l2 suggcst expert and novice assessors judge flavour character from visual data (staving effect), a feature common in humans. .\1anipulating appearance changes perceptions of product character- aroma, taste and flavour89.126,187,tss. Proccsses of odour rccognition involve primary visual cortex (BA 17) activity, involving comestibility (suitability for drinking) of prod ucts22-l.

Flavour wheel presentations of whisky attributes serve useful functions in directing attention towards specific features of character, forming bases for discussions through definition of vocabularies. SpecHic reference standards facilitatc conceptualisations (knowillg an attribute) and development of parallel mental representations of concepts, important in assessor training (ISO 8586-1:1993, 8586-2:1994). Visual representation or symbols could aid recognition or memory22-l and assessor training.

WHISKY MATVRATION

Ageing new distillates in oak yiclds mature whisky. This process, central to whisky character development, gives consumer appeal. Maturing can be considered replacement of p11ngrmt, SOOJ1y, so11r and lmrsll notes in new distillates with smootll, matured and meilaumess attributes. Such judgements also employ pattem rccognition22t with collections of stimuli from sensory systems (visual, olfactory, gustatory and chemesthesis),

Pan·ption Macroscopie lew!

inlegrating in specific brain regions to farm macroscopie representations232 of whiskics {Fig. 1}.

Research on model and malt whiskies-16--18,51 suggests wood maturations change partitioning of key flavour components with less desirabie flavour notes-19,so, increasing retcntion in liquid phases, recently simulatedHB.

Fatty acid ethyl esters, amphiphi1es with central polar groups and peripheral hydrophobic aliphatic carbon chains, are important in stabilising whisky headspace compositions2os. Structure influences solubility in aqueous ethanol: excess esters form agglomerates2S5, yielding microemulsions. At 23% (abv), agglomeratc diameters increase190 forming hazes90.I95. Chili filtration, prior to bottling, removes excess agglomerates- changing congener composition but not sensory quality2os. Agglomcrates are dominaled by ethyl dodecanoate (laurate, C12), tetradecanoate (myristate, Cl4) and hexadecanoate (palmitate, C16), contributions determined by aliphatic chain length.Jl\,48. Othcr congeners - alcohols, aldehydes and acids-also contribute to agglomerates-19,

influencing sensory character.

In wood maturationS1 non-volatile components, including sterols and tannic acids, stabilise ester agglomerates·HI,J<Jo. Temperature influcnces both agglomerate behaviour and distribution of flavouractive congeners between salution and headspace phases5o. At oral temperatures, agglomerates suppress volatile congeners more efficienttyso, but differences between nosing and tastingare thought generally smaii202. In summary, in agglomerate formation congener activity coefficients are increased by extracted wood componcnts.

Alcohol strength influcnces congener distribution45 nnd spirit matrix structurcs. Below 20% abv, ethanol

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Origins of Flm•our in Wlziskies aud a Rel'Îsetf Flavour Wllt'd: a Rl'View Volume 107, No. 5, 2001

molecules are mono-dispersed in water; between 20 and 57~ri ab\', ethanol mok-cules progressivt.• aggregate to reduce alkyl chain hydrophobk hydration and abow 57% ab\', solutions arl' ethanolic with toss of water hydrogen-bonded networks. lncrcasing ethanol conccntration lowers interfadal tension between aqueuus phases and ethyl esters, increasing aroma thresholds45. Reducing bottling strength (40% to 30-35% abv) incrcast..>s headspacc partilion coefficients, decreasing aroma thresholds influcncing longer-chain soap-like esters. Bottling strength thus influences pcrceived spirit qualityH. Dilution of a whisky to 23"/., abv maximiSL'S \'olatile release from distillates, optimising sensory assessment.

WHISKY PRODUCTION

Malt, grain and blcnded Scotch whiskies differ in production process (Fig. 2). In malt whiskies (4'Yo market

I BARI.EY

~ \\ah:r ~

!48h.l6"0

• p.:at ~mol..: I • sulphur t

Mali \ • r.ll•tlcl t

I Mll.I.J~(j Gml J

• \\ah:r

' ·~h. f>4''n I :-.t:\SIIIS<i I hlnauon Won ·}.:ast \

sale by volume - UK Food & Drinks Report, 1999) parameters in batch (pot) distillations of washes from barley rnalts influence final charactcrs2.173,273. Crain whisky is a product of continuous fractional distillation 186

of fermented wheat and maizel69, saccharified by lightlykilned barley maJts2.00. Dominant (90% market) are blends of grain (60-80%) and malt (20-40%) whiskiL-s with lighter grain (2-3) providing a flavour background, and single malts (up to .JO) the majority of character. Selection of primary (top-tiressing) and secondary rnalts has significant impactsl69• Maturations influence final flavour in blends or single whiskies with cask management ensuring product consistency31.151.165.

A REVISED WHISKY FLAVOUR WHEEL FOR SENSORY ANALYSIS

The flavour wheel of Shortreed and coworkers2.13

ordered attributes in classifications based on production.

I (iRAI:'\S I tma11.:. "h.:;ll or ~"'

I ~lii.I.I~G I : <iri'l or ''hol~ 11ram : · '' at.:r & \t.:;ttÏI f · pr.:rnah

('OOKI~G 1·:! hh. lb5 Tl

: C••uhn~t6H'l'l : • 111.11t C lU· I ~·" 1

'

J \\·a~h : f tK•u;tl>\1 +

~-----------------, r------------------, Pol I>ISTII.LATIOl'o: C'onlînuous J>ISTJI.LATION

:

[.J>L\1'\ BRITISII SI'IRI I lt ''~ K• .. ,,t-.q

FIG. 2. Production of Scotch whisky.

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Volume 107, No. 5, 2001 Origins of Flavour i11 Wlliskies and a Reuised Flavour Wheel: tl Review

FIG. 3. Revised Scotch whisky flavour wheel for industrial purposcs.

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Origins of Ffm,our in Wlliskit.•s mui a Rt•vised Flavour Wlteel: a Rc·view Volume 10ï, No. 5, 2001

T ABLE L Whisky descriptors and referencl' compounds.

Code Flavour Wheeltenn

N.l Pungl!nt

A. I. 2 Burnt .mwky

A.3 .\lt!dtnndl

B.2 .\lclll)'

Cl GrcU.'i_\'

0.1 Solwn~\·

D:? Frm(\'ltlppl!!,\'1

D.3 Frui~r fhmiWid. pc!Cir-dropJ

0.5 Berry

Caur

E.l Floreli t.\'cJ/Urul - roseJ

- woll!t

f'/oral t.·lt·utics,t/ St'~'llh'd Pl'l'/llllll'(IJ

G.5 .\'llf~l' koCOilll/)

mar:tpcm

G.6 l't~nilhl

G.7 Spl(\.

Splt')' (dow)

G.8 ( 'ar.mh!l(t'!llll~\·.fln'îsl

G.IO .\loih/'la/1

Rcterence compounds tor assessor training Fonnic acid 1

.. ,

Guaiacol •:·•

o-Crcsol p ..

1' 1'11 I'U 2- and 3-Meth~ I butanal ' .t-Hydroxy-2(or 5 )-cth> 1-2( or 5 )-methyi-3(2H) furanone ''4 •

4-h> drox> -2.5-dimcth> 1-3(2H) furanone •u

Hcxanal •~··

cts-3-llcxcnc-1-ol 1'"'

Eth> I act:tate 1 '"

2-Mcth> I propan-l-ol I'N

1'•' Eth> I hcxanoatc ·

t ... ~. 1.\'o-Am> I acelate -

Thiomcmhonc 1'"

Thiomcnthonc 1 '"

Sodium sullidc · mcsit> I oxidc 1'~''

l"l•J Phcn> l ethanol ·

a-.jJ-Ionunc <a

Gcraniul 1 ~ ..

Whisk> la..:tonc •=··

Furfural •:·•

Vanillin ·~··

-I-Vin~ I guaiacol 1:··

Eugcno1 129'199

\ 1altol •:··

'aphthalcnc

joumal of The lnstitute of Brewing

Concentrat ion (mg litrc 1)

10 x 10'

27

1.75

0.6 (2-meth\ I butanal) m · 1.25 ( 3-methvl butanal) 1 ~~ •

5

1.00 x 10'

1.12 x 10'

1.00 x 101

")

7

3x 10·'

1.26

100 cach

1.52 x 101

>3Xl0-·1

19

:!66

839

~3

71

- 55

1.1-l \ 10'

>8XI0-3

291


Vollmu• 107, No. 5, 2001 Orisins of Flavour i11 W/liskies and a Revised Flavour Wltt•e/: a Rt'ï.liew

G.ll

G.l2

1.1

1.1.6

J.2

1.3

J.5

k.l

L.

L.l

L.2

.\luuldy

Eurti~L mu.sty

lïnegury

CurdhuurJ

Sragmmt. ruhhery

Rutten egg

Meaty

l"egelcthh• (sweet corn. cookeJ mhhuge)

Oi~r

Suupy

Buttery

2.4 ,6-Ttrichloroanisole

Geosmin. 2-methyltsu-bomeol ~;· 69

Acetic acid 1 ~<~

2-Nonenal ~>u

Dimeth~ I tri-sulphide (OMTS) 1 ~8

Hydrogen sulphide m

Methyl (2-methyl-3-furyl) disulphides ~ 7

Dimethyl sulphide (DMS) m

Ethancthiol 1:

8

3-Mcth~ 1-2-butene-1-thiol 118

n-Butyric acid' ethyl buryrate ~6

t.w- V a Ie: ric acid 1 :.,

Heptanol ""'

1"9 Eth) I laurate ·

1-Decanol •• ,.,

Diacctyl I:•J

, ~ - '· C.. ~a.

10

5.32 x 10'

0.08

3

>0.02

>0.14

> 0.6

> 0.072

> 7.2 x 10""'

>2

2

12

100

0.1

( 199) - 23° o ethanol solution: (I i9) - in :n~ o grain whiksy: ( 128)- in lager: (26. 27. 54. 69. 94. 130, 199. 237)- > threshold: (155) - thrcshold in beer

c Hybrid structures consiclering production and flavour Nasaleffects perception are more likely to be of industrial value. The revised whisky flavour whL>cl (Fig. 3), similar to other alcoholic drinksl57,I79, has a hierarchy of three tiers: primary - production origin or generality of nature; secondary - specific sensory or conceptuni descriptors; and tertiary - highly specific terms, certain of technical importance. Attributes, in clockwise order, are on the right arising in normal production suitable for promotional and marketing purposes. On the left, offnotes, for tcchnical functions, form four groups.

In the revision, primary tier chemica! terms (pllenolic, aldeltydic, esten;J were substituted with common industrial terms (IJt•aty/smoky, grassy, fruity and flora/, rcspectively). The gencric feinfsl41 was not replaced as of industrial value. Blenders and sensory assessors in Scotch whiskyl29

more often usc subtier terms. For assessor training, reference compounds are recommendcd (Table 1): formulations with cyclodextrins achieve consistcncy and parallel conceptualisations.

N.l. p1111gency- ethanolic, I'L'ppery, prickle N.2. dryius

Pungmcy, a primary common chemica) sense (irritation, chcmesthesis)t2t, originates in delocalised stimulation of trigeminal nerve endings2st - a sharp, stillging or parfini SL'IIsatiotl of flavour or odour'. Individuals are generally more sensitive to aroma notes than prmgency2.'13,

In maturations, punge11cy is generally replaced by snwotlmessll5,206. Etlrallo!ic-ptmgency, often ascribed to ethanol content, is not solcly from spirit strength: activity of headspace ethyl esters also contributes2SI. The off-note peppery-pwzge11cy originates in bacterial, notably Lactobaci!Jusi05,13!!,ti>0,24I spp., fermentations producing acroleinl05,trlll, at elevated tcmperatures or in extended fermentations24t, from glycerol from yeast catabolism. The product, ~-hydroxy propionaldehyde, is in distillation31! degraded to lachrymatory acrolein - inducing pwzgent, lmrnt and peppery notes'JO, red eyest60. Wooden washbacks

292 Journat of The lnstitute of Brewing


Ori,~itls of FlmYour in Wlliskics aud a Rt'1.list'd Fla·oour Wllt't'l: a Reoit•w Volume 107, No. 5, 2001

J OII

0 ( 11 ( lil 111 111

p·Coumar~ I ilkohul

' (JIJ

~

~ UIUilll€1

p-Coumar~ l<tldch~ de

' OI!

~ • I

I

~ UI (."JI( ()(lil

p-Cournaric acid

' ntt ~

~ UI l 11.

4-Vin) I phcnul

' 1111

0 \"11..(11

.a-Erh~ I phc:nol

I u 111

OJI ~(I( 11

.... ~

lil

l.ignin

!!OI!

' \\'ood-lignm (\·fl) Ethanol-lignin c n J

I 11 111

' 1111

~<Kil

~ l 11 (. 111. lil lil

Conifc~ I alcohol

' OI I

~IKII

~ UI l lil 1111

Conili:raldch~ de ( Fcrulalûd1~ 1.!1: J

' 1111 ~lllll ' i .

~ lil l lil I K 111

' OII .~(I( 11

~ lil Cll.

I 11 111

OJI

tii<~IIUI I

~ t 11 ·Uit 11011

Sinilpyl alcohol

' oll

lff.( ~0("11,

V lii•UIUIO

Si na pa ldchy·dc

0 " #> r),, ll, .. 0 .. "· lll··o·x.,,.

l'll (."!I< 11011 CliO Sinapic acid S) ringaldch~ de

Oll

~11(.11

'-..../ UX.ll .

' OI!

lil 1011(11.

~ ltlOII

S> ring ie <~cid .a-\lt:th~ 1-guai<u:ol -l- Vin~ 1-guaiilcul Acchl\ anillitmc

011

~lllll

~ 4..11.-t 11

' OII

~IH.II .... ~

l 1111

011 ~()(.'JI 'I !

~ Ollïl:lll

-l-FII•~ 1-guaiacol \' anillm PropÎO\<Inillionc:

' i_ill /~lllll

'-...../ t (u •11

\ •• 111 illic ;u: u.l

J!; 1111

~11\ll I

'-...../

Guaiacol

" ( 111

~IJ(,JJ

l CIO(. )I,

l:!h ~ I \ iln i llatc

FIG. 4. Lignin-derived aromatic aldehyde transformations in whisky.

joumal of Thc lnstitutc of Brcwing 293

This document is provided com

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._ :i '~ .~,.

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11 Aronmlic aldehydes S 5' • Al I Poly phcnnls Phcnols

til ~ euron ayer .. Ph 1. . ~ .. ,..,. ,.,. h . d . . cno •c acad Van1lhn etc. ;::;: :::.. - en:mc an crnnum1c t.: c ::. 1 . . ._, (sec ,-u.~ 4) ~ tf; • w!rn·atn·C!.~ <l<."luS -

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R-CJI-CO!H • R1-C-C-Rl ___., R-CHO + R 1 -CH-C-R~

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Origins of Flm,our in Wlliskit.>s anti a Revised Fltnmur Wl!ee/: a Review Volume 10ï, No. 5, 2001

are sourc(.>S of bacterial contamination but pH, oxygen tension, agitation, presencc of yeast cells and/or mash residue, fcrmcntablc sugars and glycerol influence acrolcin production 16°. Aftcr 2-3 maturation years, these off-flavours disappcar: acrolein reacts with ethanol yicld ing L 1-d iethoxy-2-propene:ls,ns, 1,1,3 triethoxypropanc, 3-ethoxypropionaldehyde and propenelll5.ll~<'•.li7. None possesses unpleasant notes or lachrymatory effccts. PeJ'I'ery attributes should bc discriminat<.>d from SJ'ÎC.tf-l'''l'l'ery character from certain casks.

Phenolic characters

A. Peaty character

A.l. lmml-ltlrry, S«)(J/y, asll

A.2. snwky- wood smoke, kil'l1f.'ry, snwkt'tl lmccm/chet>se

A.3. IIU'didual- TCP, autise1Jfic, gt.•rmolim.', Ilospital

Smoky is linked to degraded wood carbohydrates -cellulose, hcmicclluloses and lignins:lï. Peaty attributes originate in smokc, introduced into the airflow during thc kilning proccssesl1.12, from phenolic compounds280 and also sulphur- and nitrogen congeners, pyridines and thiazok>s. Quantitatively important are phenol, cn.>Sols (m-, o-, 1'·), xylenols, and t'· and m-elhylphenol. Guaiacol has low flavour thresholds (3 J.tg lilre-l in 10% spiritll~>; detcction, 0.09 f.lg litre-1 and recognition 3 J.tg lître-1 127) and subslitutcd methoxy phenols278 have significant flavour impacts. Important volatiles for desirabie smoke flavour are abundant in phenolic and basic subfractions, addic and neutral are of secondary importance:lï.

Although kilning uses alternative fuels, indusion of short-time intensive peat combuslion yields a characteristic reek. Smoke absorption is maximal at 15-30'Yo moisturc in malting barleyll. Raising kilning from 400 to 750°C yiclds scveral-fold increases in phenol and cresol, reducing guaiacoJII, Thomson25ï has reviewed relalionships between flavour-active phcnols, peat composition and kilning. Charring stave surfaces introduces s11wky attributes following extraction of thermally degradcd lignins (Fig. 4) with ethanolysis of Braun's ligninlïn. Thc resulting aromatic aldehydes inducc swet'lncss and smoky attributcs-13.44. Othcr phenolics - e.g. benzoic, cinnamic, ferulic (4-hydroxy-3-methoxycinnamic)'l'J, JI·Coumaric (4-hydroxycinnamic) and sinapic acids- originated in eercal ccll walls (Fig. 5) and are transformcd into phenols by kilning, thermal dccarboxylations2ól. Fendie and l'·coumaric acids yield 4-vinyl guaiacol and 4-ethyl phenols, respectively (Fig. 4), through yeast dccarboxylations36.59.66.243, particularly in spirits from ryc abundant in phcnolic acids189.

Hydrophilicity in phcnols ensures feint relention limiting final whisky concentration9S,t89. Phenol dominates (46-:67%) in peated barley malt, eresols

(58-61%) final spirit. Bolh, from peated malts, influence character of Scotch, Spanish and japanese whiskies67. 0-cresol is most abundant in Scotch whisky wilh thresholds of 31 mg litre-t in 10% spirit66 and 30 and 120 f.lg litre-t (dctection and recognition) in 23% grain whiskyt27. Phenol contributes only circa 7'Yo odour units16,225, but related attributes are important, especially in Scotch whisky2!lll with characters often described as mediciual and iodille2-'. In Speysidc rnalts lhis is more often pealy. Strong phenolic characters such as medicinal relale to kilning o- and m-crcsols, pcaty may be linked to eugenol25°. In Bourbon and Canadian whiskies unpeated, green rnalts from barley, corn or ryc, and phenol and eresols have lesser impacts on character and smoky attributcs originate in lignin breakdown components. These induded eugenol, 4-ethyl phenol and 4-cthyl guaiacol, from new stavcs aftcr charring and ethanolic cxtractionsBt (Fig. 4) or eercal cell walls. Eugcnol with low thrcsholds of 11 6f•, and deleetion at 0.5 and rccognition of 5 JJg litrc-1 127, influences Bourbon flavour61'•. Adding phenol mixtures to Bourbon mimicked Scotch whisky characters of woody with additional oily, but not c•stery and sweet attributes66.

Humic and fulvic acids in mashing watersli2.272 influencc pc•aty characters. Congeners including halogcns of marine originsli2 and microbial activity also gcnerates highly flavour-active compounds such as chloroguaiacols that at extreme dilutions yield distinctivc off-notcs, e.g. Rio character in coffee-'i5,146.240,

In the original flavour wheeJ2.13, discrimination of phenolic attributl>S was contentious with secondary tier dustering of medidnal, peaty and kipper.IJ. Relationships bctw(.>cn the strongcr mediciua/, and peaty are undearl2,250 as are thosc between JU'aly and dry attributes in whiskk>S171. No relationship between dn;uess of Scotch and total phenol content has b(.>cn demonstrated12.251, lnterestingly, a spccific volatile phcnol anosmia - partial odour blindness-is reported in 15% of the UK population for suggcsting inconsistent flavour influenccs98.

Fermentation characters

8. Graiuy characters

B.l. cm•a/ - (digt'SIÎZ't') lliscuity, llusky, bran, leatl!ery, tolmcco, mousy

B.2. malt - malt t•xtract, malled barley B.3. maslt -l'orrid:.:e, draf!, wort, cooked maize

Graiuy charactcrs, unlinked to any specific congener, are regarded by disUilers as important. Raw materials, grains or cookcd grain (masll) form referencc standard. Green rnalts confer fruity, lmy-likc, and damp-strmv notes, replact..>d by lmmt, l'reatiy, malty and clwcolatc-like notest4 with increased kilning temperatures. Maillard browning inlermcdiatcs interact with eercal lipid oxidation products (Fig. 5).

Joumal of The lnstitute of Brewing 295


Volumt• 107, No. 5, 2001 Origi11s of F/avo11r in Wlliskies mzd a Revised Flnmur Wlzee/: a Rt:.z•iew

:\l..;ulwl Sarc:ngth ("'• \: \')

I) •••

!·\mesh ol $

I ..... ___ i .......

.11 :\knhullc slrcngch (ldt .lxtsl cl tso-Bulanol tnght a:usJ cl Ocranou; acu.l tnght axts)

d

'·

• o vl ~l.lXllllUIII

c .. ngcncr l .. m..:cnlr;lllorl

I . 100

- . . . ···'-········-···------: 0 Fcmls

hl 1:1hyl dcc.muale {rt~hc <txts) dl Dccanmc .tetJ (nght ax1s)

t'l Phenclhyl -.:1hanol (nghl axts)

FIG. 6. Fracti~~1l ~is~illa~ion Fon•shots, Spirit, Feints- and profiling of akoholic strength and fivc whisky congeners during a laboratory spmt dtsttllat1on (Goodall, !'I tri, 1999; reproduccd with pcrrnission from lusfit u te of Bmt•iug, 1999, 105).

Furfural, grainy at 20-30 mg/litrc in Scotch whisky13fl, may contributc to ltOliii.'SS in spirits!l6.238. At 90% recognition threshold (839 mg/litre)l29 furfural was described by fcw distillers (<10'}';,) as gminy, more used was marzipall (cocomlf, cake mix, nlmotrd, 11/lltlf, waltwt oil and coumarin-like - 54%), swet•t (26%) and of/lf (15%)129.

Pentose sugars, from breakdown of eercal .cell walls, yield furfural during pyrolysis in malting and distillationt2,tï.tï~>.338 (Fig. 5): concentrations are functions of wash pH espedally with high numbers of Jactic bactcrial7.

In whole and ground ccreals22<~, aldehydes, enals, 2,3-butanediols, acetic acid, and chloro- and bromomethoxybenzenes dominate volatiles. Thc last is associated with musty in sorghums. In maltst3 malty is associated with 2- and 3-methylbutanal, linked to wortv in alcohol-free beert 93,19~. Perpète and Collin193,19~ associated worty primarily with 3-methylthiopropionaldehyde but other compounds influencing malty or cereal-like characler indudc ethylmethylpyrazim.'S, maltoJ13 and hydmxydimethylfuranone from 2-mcthylpropanaFl. Fermentcd malt extracts typically contain 4-hydmxy·S{or 2)-ethyl-2(or 5)-methyi-3(2H)furanone (HEMF) and 4-hydroxy-2,5-dimethyi-3(2H) furanone (HDMF). All producL'li in beer by Saccllaromyces cert'Visiat.9.1 have sweet, mally and caramel notcs.

Aldehydic ebaraders

C. Grassy character

C.l. fresll Jeafy, wet/cut gmss, flowt•r slem, green npple/ /Jmrmm

C.2. dricd - llay, straw, tea, mi11f, lterhal

Gmssy is often synonymous with alddtydic, green and leafy attributes2.n but the technica! - altlellydic - is better understood as freslt and dried grassyl29. GrasS~J is better ddined than green. widely used for immaturity in wines fymm:~J, from green malt usage2.13 and multifaceted in perfumeryw:!. Grassy notes from hexanal are pcrceived ttlmoml by a minority (12'Yo) of asscssors12<1.

Many compounds relale to grassy characters in whisky2ó,ttlb,241•·247,25t,278 including low molecular weight aldehydes e.g. hcxanal, trans-2-hexenal, 2- and 3-hexenol. These confer green leaves, grassy and even fruity notes. lncreasing aliphatic chain length yiclds less pleasant cardll(mrtl-/ike and bitter notesl56. Aldehydes originate in barley lipids, dominated by 9,12-octadecadienoic (linoleic), 9,12,15- octadecatrienoic (linolenic) and 9-octadecenoic (oleic) adds. Malt lipoxygenases oxidise linolcnic and 6,10,14,18-eicosatetraenoic (arachidonic) adds (Fig. 5), yielding 9- and 13-hydropcroxides and further aldehydes: hexanal, trans-2-hexenall89, 2- and 3-hexcnol (leaf alcohoJ)54.l02 and unsaturated methyl kctones (6-tridcccn-2-one, 6-pentadccen-2-one and 6-hcptadccen-2-one)175.

Estery characters

Estcry characters are ordered as in the original wheetm, and include soll'ellty, fruity, flora/, and feinty, functions of aliphatic chain length21Q. In distillations, sofl,t•nty and fmity, are rclated to hcads (foreshot), passing to flora/ and fi•i1lls (tails) as distillntion procecds66.189

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Origius of Flavour i11 Whiskies rmd a Hevised Flavour Wlwel: a fkpit•w Volume 107, No. 5, 2001

(Fig. 6). Spirit cut-off points are central to estery charactcrst73.tS9 and differ between distillcrics. Although individual esters showed lessimpacts on whisky flavour, in total, esters form a key component of flavour225, contributing particularly to complex rmmdlless25t.

In fermcntations, acetyl CoA reacts with frcc alcohols to form esters at rates which are inverscly related to aliphatic chain length, and yiclds dctermincd by fatty acids concentrationst89 (Fig. 5). Effcctive concentrations vary: ethyl caproate (C6) is released into wash, lauratc (C12) largely retained within yeast ccllstso. Fcrmentation ester formation is influenced by \\'Ort gravity2t5, yeast strain93 and pitching ratellf>.214, wort unsaturated fatty acid concentrationtR.t38.259, acrationtn,2:W and temperaturel59 .

Mass transfer of substrates, and yeast growth, are kcy factors for wort levels of medium-chain fatty acidsl8.

In maturation, furthcr esterification of fatty acids2tf> occurs, and ethyl acetatct77 bl'Comt..'S abundant originating in acetic acid from hydrolysis of hemicellulose acct)•l groupsl76, oxidation of ethanol, and wood charring37. Equilibria cxist between acetaldehyde and ethyl acctate; betwl>cn ester and acetic acid and ethanol. Certain acids, notably hexanoic (caproic, C6) and tetradecanok (myristic, C14), react slowly in maturations and othersethyl dccanoate (capratc, ClO), hcxadccanoate (palmitatc, C16) and 9,12,15-octadecatrienoate (linolcatc: C18) show significant rcvcrse rcactionsi77.2tn.

The first-Hght fraction (foreshots)

D. Fmity characters

D.l. soll't'lll_ll- nnill•mlislt rcuwz•t•r, paint thinner, fusel oil

D.2. orclltlrd- fll'l'ie, l'caclws, pt•nr 0.3. froJJicnl- pitteni'Pie, mt•lon, /lnnmw (pcar-drop) D.4. citrus- orange, it'mon, graJ1tfruit, :est 0.5. l1erries- blackcurrant, tomalo t'laut, catty 0.6. dried - raisi11s, figs, l'rrmes

Ester characters - e.g. from ethyl acetate the most abundant at (typically) 175 mg litrc-l in whisky18- are often perceived solvent-like. Ethyl acetate has high thrcsholds of between 33156 and 74 mg litrc-t t95 with deleetion and recognition thresholds in 23'Yo (abv) grain spirit of 14 and 100 mg litre-1, rt..'Spcctivelyl27. Howcver, esters show synergistic and supprcssion effects that could influence overall character201.

Short-chain alcohol esters (forcshots) (Fig. 6) -ethyl, iso-butyl and iso-amyl esters and iso-amyl alcohol are perccived as fruity, mainly banana or apple. These congeners influence quality in rclation to spirit content of fusel oils: in whiskics ethyl acctate and related esters, impart pear-drop characterst73.

Drit>d-Jntify notes in dried bell peppersi37 are linked with 2-mcthylpropanal, and 2- and 3-methylbutanal, also linkcd to mnlty and worty notest3,193.1'14 in malts.

The middle fraction (spirit)

This fr,lction is abundant in ethyl hcxanoate (caproate, C6), octanoatc (caprylate, C8), dccanoate (caprate, ClO), dodecanoate (laurate, C12) and lactate, which are important in whisky flavour::!::!5. Ethyl hexanoate (caproatc, C6) imparts fruity (app/t>y) characters and with incrcasing l'Ster chain length soapy, aily and sour notes, rdated to whisky immaturityt0.2o5. Such notes, abundant in later stages of batch distillation, are associated with l'lhyl octanoate (caprylatc, C8) and esters of tetradl'canoic (myristic, C14), and hexadecanoic (palmitic, C16) and hexadecenoic (palmitoleic, C18) acids.

The tail fraction (feints)

Hcxanoic (caproic, C6), octanoic (caprylic, C8), dl'Canoic (capric, ClO) and dodecanoic (lauric, C12) acids and esters of dodecanoic (lauric, C12), tetradecanok (myristic, C14), hexadecanoic (palmitic, C16) and hexadl'ccnoic (palmitoleic, C16:1) acids yield soapy, oily, sour and fdnts in distillates, often discardcd as tails87. Exccss higher fatty acid esters (>C11,) causc chili haze in spirit reductions to bottling strengthli.UOR and are Jess desirabic in ncw distillates41.1!2 (Fig. 6). Yeast in wash at distillation enhances concentrations245. Propanol, isobutanol, amyl and iso-amyl alcohols are present in head and fcints fraction. Feillts notes, infrcquent in early spirit fractionsll>H, are linked to certain fatty acids and sulphur congeners (e.g. dimethyl trisulphidc) in tai)sl68,

E. Flora/ characters

E.l. natura/ - rose, lavendcr, vioft>t, ll/ucbcll, camatio11, lu·atl1ct~ lwney

E.2. artificia/-Jrngrant, scentt>d, perfumed

In feints phenylethyl ethanol coofcrs flora/, rose-tvaler and fragrallt notes; ~-damascenonc, an impact compound in Damascus rose oil57.ss, imparts fragrtml with dilution to 23% (abv)l'~5. This ~-damasccnone has a high odour unit value (2500) in whisky, but low intcnsity index limits detectiont95. Autoxidation of vitamin A or lipids, from ycast or barley54, and breakdown of oak norisoprenoids41 yields a- and P-ionones with violet-like nol es.

F. Feiuts charaders

F.l. grainy: see section B F.2. clu·csy: see section K F.3. oily: sec scction L F.4. sulplmry: see section J

Exccss jci11ts notes influence distillate quality172. Notes includc leatlzL•ry or cereal-likc ( cooked maslr, biscuity) passing



Volumt• 107, No. 5, 2001 Ori~i11s c~f Flavour i11 Wlliskies and a Rt•l'ised Flm•cmr Wlu·t'l: a Review

to sweaty (piggen;> and into stalefisll characters2.>J. 5wt'lll!f is related to isovaleric acid contcntlt~'l. Feints, with distinctive stale notes and metallic aftertastell, have abundant malt-derived phcnols and DMT527.

Maturation characters

G. Woody character

White oak wood (e.g. Quercus al/la) varil•s in contents17 of cellulose (49-52%), lignin (31-33%), hemicellulose (22':<,) and extraetabie compounds: volatilc lipids, volatile and non-volatile acids, sugars, stcroids, tannic substances, pigments and inorganic compoundsl77. Heartwood contain more lipids: triglyceridcs of Cu~ unsaturated and clh saturated fatty acids, sterols and a fcrulic acid ester with a C.10 wax alcoho)238. All have gradual impacts with cask agcing and sterols producing hazes during spirit rcduction for bottlingns.

Cellulose (a glucose homopolymer) is central to oakwood structure with hemicclluloses (hcterogenous polymers) forming matrices and lignin an adhcsive cncrustant. Cell wal) Jignin (70%) is linked to hcmicelluloses in a three-dimcnsional complex dominated by phenylpropane derivativcs of guaiacyl (2-methoxyphenol) and syringyl (2,6-dimethoxyphenol) units with aliphatic and aromatic intermonomcr covalent bands. Linkages between lignin, tannins and thc carbohydrates make fractionation difficult and insolubility reduces flavour impact. However, breakdown produels and related extractives influence flavour23x conferring smoky37 and lt'tlody characters. In charring lignins are more stabic than polysaccharides37. In acidic (-pH 4.5) wood maturations17n insoluble hemicelluloses slowly depolymerise and are extractceL

Woody characters are complex in both whisky and wines178. Important contributors includc lipid-derived whisky Jactoncs, and lignin breakdown compounds -vanillin, and relatcd aromatic aldehydes, and derived acids, esters, tannins and sugars. Pérez-Coello and coworkersl92 regarded cis- and lmlls-lactones, eugenol, vanillin and syringaldehydc as the volatiles with grcatcst sensory impact with optima for extraelions of vanillin and syringaldehyde of 165-215 ocm. A syringaldehydc/vanillin ratio of l .4/2.5 indicates balanccd decomposition of oak lignin197. lntcractions between certain lactones and vanillin are important at concentrations present in Scotch whisky enhancing vanilla character (Swan, J., unpublishcd). Certain wood phenolics, notably vanillin (3-formyl-2-methoxyphenol), syringaldehydc and 5-hydroxy methyl-2-furfuraldehyde are markers of good spirit quality. The origins appcar desirabie stavcs with abundant earlywood with many annual rings cm-1 (maximum 12)218.

NykäncniSI concluded that hydralysis of ligninhcmicellulose complexes was more important than cthanolysis as caskwood absorbs water in preferenee to

ethanol. However, ethanol activity is maximal at cask strength (60% abv). This enhanccs solubility of key congcners, acids and phcnolics that with derived oxidation products, confer important characters -malurity, roundness, well-bnlanced and smoofll112. Woody attributes are subdivided into: new wood, extractive and defectivc staves.

New wood characters

G.l. sap - grem bark, wet wood G.2. cedar- sml'du:;t, cardboard, slwrpL'IIed J1L'IIcil G.J. oak- resi11, polislt GA. pi1u·- turpe11tille, rctsi11a

Freslt sawdust or sap notes originating in new barrels, are related to wood origin, and eliminateel with second useage:l2. In wines32, unpleasant sawdusl notcs are linked to (E)-2-noncnal (ml!cid in beerl0.21'2), 3-octen-1-onc, (E)-2-octcnal and I -decanal. These compounds, associatcd with can/l)()ard in whiskiesl:lll and other products1'16.277, originate in linoleic acid oxidation" in unsaturated barlcy lipids. Cask toasting processes reduce (E)-2-octcnal, and associated notcs, in maturcd wines32.

Higher akoholic strength fillings rcduce extraction of wood-dcrivcd components and associated notes23s. In an H-year old whisky, filled at 59'Y., abv, character was ./1m•oun•d, at 63'}'o kss mntured and weakt•r and at 77% gree11 oakl77,2:1s. In cognac, extractions of phenolic acids, aromatic aldehydes, acctals, ethyl butyrate, medium chain fatty acid esters (CS, 10 & 12), were maximal at 60-70'~<. abv; sugars, polyols, ethyl acetate, and acetic and short chain fatty acids (C3, -l & 5) at 40-50'1-;, abv24. For balanced extraelions thc optimum was 50-55~;,

abv24, typkal of armagnac.

Wood extractive characters

C.S. 11111/y - cocollllf, l1t1::el 1111/, almond/man:ipmr, wal1111/

Nutty is associated with a product of oak lipid oxidation, described as "whisky lactone", "3-mcthyl-.J-octanolides", "13-mcthyl-y-octalactone", "5-butyl-.J-methyl-dihydro-2(31-1 )-furanone", or "Quercus lactonc". Associatcd flavour character is conmut at high concentrations (>5.3 mg litrc-1) and oak wood-likt· at lower (0.1 mg litre-1)13'1,2JI. This lactone, togcther with 4-nonanolide and eugcnol""·l54, are major volatile congeners derivcd solely from oak142.2:ls. A possible lactone precursor is 2-methyl-3-(3,4-dihydroxy-5-methoxybenzo)-octanoic acid152,Js3.

Four lactone isomers are, cis-(3R,.J/V, cis-(35,45), lral!s(35,.J/{) and tralls-(3R,45), differing in flavour character (1~1ble 11)83. Oak contains only ds-(35,45) and tralls(35,4/{)1';2,153: other isomers indicate synthetic lactones in flavouring/ ageing agentsl-t3,1t>4. Misidentification of isomcrs21.111l.l-t2.149,18-l has produccd contradictory cis:trcms ratios, and threshold values:l:l.l-t2.11•\1H-t.

298 Joumal of The lnstitute of Brewing


Ori:\ills <~f Flamur in Wlliskies muf a /~episcd Flamur Wl1cd: 11 lki•it·w Volum(' 107, No. 5, 2001

T ABLE 11. T.1ste and odour propl.'rtkos of o.1k l.lCtont.>s.

Compound Taste

c:is-(3R..IR) Creamy. cocmwt 5iweet. wom~l-. ,·oc:onlll

,·ü-(3S..IS) 5,iJicy. ,·oc:mwt-lih• Ught coconut. musty. hay

m.m.H3R.-IS) .\"ph:r ( 'onmut. odet)·

(Günthcr ct al.. 1986: rcproduccd "ith pl.'rmi~sion from l.tt•htg., ..lnnah•n dt•r Clremu:. 1986. 2112 I

For racemie mixture of 1,1ctoncs, dctection and rccognition thresholds wcrc: 0.5 nnd 1 mg litre·l, rcspectively in 23% grain whiskyl27 but 0.05 mg litre-l 225 in 3-l% nbv grain spirit; în whitc nnd red wines 120 and 125 Jlg litrc-1 :4. Reported diffcrcncc thresholds are 2-1:1 mg litrc-• in white, 853 in rl•d winl' and 75 in 12"<• abv cthanol211-l. In white wine lactonc confcrs musty notes, in red /mrsll and in 12% ethanol cocmwl, woody and oaky2n4 linked to thc more abundant eb isomer (Table 11) \vith a thrcshold of 0.092 mg litrc-1, 2.5-20 times lowcr than /musl~>t. Wood origins can bc rl'laled lo lactone ratiol<~2, fl'portcdt~-~ 77:23 (cis:trtms) in wond but dependent on cask history and treatmcnt. Thc cis lactone is more abundant in American whitc oaks than Pcdunculate or St..ossîlcm. Ratios (cis:tmnsJ a lso vary through single staves, with cis maximal (250 mg kg-l of wood), and more cxtractablet-B, at 5 mm bclow stave surface and trans maximnl (48 mg kg-') at 15 mm depth+I.

Lactoncs have been studicd extcnsively as important in wine characters1,2tJ.l. Waterhouse nnd coworkers2ïl hnw controvcrsially daimed ratios in wine maturation onks {European versus Amcrican onk) suggest white oaks showed fixed ratios of cis to trmts oak lactone, delermined geneticallyt.n. American whitc oak tQuercus a/ba) heartwood contilins five-fold more lactone and prt.>cursor lipidsl42 than sapwood: two 3-oxo-retrocx-ionol isomers serve as markers. However, eugenol and vanillin concentrations are similar in American and European oaks3t. Europcan pedunculate oak (Quercus robur), low in aromatics and high in cllagitnnnin, is best suited to ageing spirits; Europenn scssilc (Querws Jlt'frtlf'fl) and Amerkan white oak to maturing wine:lt. Ncw Bourbon casks have tcn-fold higher extraetabie lactoncs than Scotch casks at 0.047-0.25-lJJg kg-l: flavour impact is rL>duccd by cask usagc-t-t. "Standard" Scotch whisky have been reported containing 0.96, "premium" 1.16, and a "high" had 2.17 mg litre-t total lactonclt~-~. Similar correlations between lactone conccntrations and quality gradc cxist in cognacslll-1, There is conversion of trans to more stable, flavour-active cis form in bottie maturation of wine35.

Thcrmal lipid oxidationsl42 in cask charring iocrcases lactonc up to thrL>e-fold but exccss tempcratures reduce surface conlcnt:lJ,J.IJ. Lactone is retaincd dL>cper in staves, and bclow chars. Care during charring is beneficia) as changes in cis/trm1s ratio will influcnce characterm. In wincs (e.g Chardonnay), green oak yickls muilla, buttery, 1111/ty, caramel, et•dar, conmut, raisin and dil/ notes, and incrcases spicy charactcrs227. In contrast, seasoned wood incrcascs cedar and 1111tty notcs, dccrcasing misin7-t,227.

Othcr lnctoncs, y-nonalactone (C9L), y-dccalactone (CIOL) and y-dodecalactone (C12L) me found in mature and immature malt whiskies, impartingfatty, and sweet ntllcs - partkularly ClOL and C12L in malt whisky2f•9•

Ccrtain ycasts, notably S;mrol,o/omyct•s, in spccific wines and flor sherries, excrctc 4-dccanolide and cis-6-dodcccn--l-olidetS.tó7.

C.6. l'llllilltl - ice cremu, cusltmf, toffl'e, clwcolate, cake mix, cola

Vaui/la, often described cimcolale and cola through "circlc minded" associationsHl2, is important in certain whiskics. New casks are toastcd to eliminale IU'W-wood nolcs and astriugellf tastcs, with an optimum of 165-215°CI51 for Bourbons. Charring increases contents of vanillin, vanillic acid and rclatcd compounds acctovanillonc and propiovanillonc, and othcr lignin aldehydes coniferaldchyde, sinapaldehyde, ncetosyringone- and their acidsl77. Aldehydes are oxidiscd to acids or convcrled to vanillin and syringaldehydc contributing to muil/a (Fig. 4)176,177 with cffccts.&0,51l,l76,217 including synergistic intcractions (Tablc IJI)I:w. Clyne-to linked incrcascd vanillin and syringaldehyde in whisky from charred casks with smoollt, muil/in, sweet, malty, SJIÏL1J.fruity and flora/ notes rcminiscent of Bourbon whiskcy. Whisky matured in unchnrrcd casks had higher contcnts of coniferaldehyde, sinlipaldehyde and vanillic acid with tmngent, grainy, sour, oily, sulplmry, cally, menty, and fislly notcs. Callic acid from tannin hydralysis is most abundant in uncharred woods, in Scotch whisky the flavour impact

joumal of The Institutc of Brewing 299


Volume 107, No. 5, 2001 Origi11s of Flar1ortr in Wltiskies and a ReviSl'd Flavour Wheel: a Review

T ABLE lil. Syngergistic effects of aromatic aldehydes in 40~C. ab\'.

Compounds Taste threshold (mg/litre)

Vanillin (V) 0.1

Syringaldchydc ( Y) 15

Sinapaldchyd~ (I) 50

Ferulic acid (FA) 30

Vanillic acid (VA) ,-_, Syringic acid ( Y A) 10

Sinapic acid (IA) 100

V!Y , -FA/V A/Y A/IA/V 4

FA/V A/Y A/V /Y /I ,

( Maga J. A .• I 984: rcproduccd wilh permission from f:IJ.:n~·r Sdl!n,·l!. 1984. 409)

of syringaldehyde {50% of total aldehydes) and vanillin (24°/.,)44.132,151.217 is thought greater. Increascd dissolved oxygen yields higher conccntrations of vanil.lin, syringaldehyde, coniferaldehyde, vanillic and syringic acids13<l,J76,217,2Sl. Extraction ratc is high immediately

after filling and slower during subsequent maturation promoted by hydrolysis, cthanolysis and also oxidations, at rates determined by filling strength43,238.

Thresholds for vanillin have bt.'Cn dcfined as 2 mg litre-1 in water, 0.5 and 0.1 mg litre-• in 10 and 40% ethanol solutionsH5,2.38. These scnsorially-important phenols are maximal at 5 mm below the char in ncw wood44 \.vith syringaldehyde and syringic acid more abundant than vanillin and vanillic acid. Oak wood drying (air or kiln) also influences vanillin, coniferaldehyde and syringaldehyde contents27o. Air seasoning may increase mycoflora attacking cell wall lignins and polysaccharides270, yielding compounds associated with positive maturation characters252,

G.7. spicy- clozJe, cimtatmm, giug('r, 'aromatic', uutmeg

Woody spicy attributes originatc in wood extracts, particularly eugenol, derived from lipid oxidation (Fig. 5)142,164,165, abundant in Bourbon whisky68.206, This congener has a thresholds 2-34 ~g litre-t in beers151i, 11 and 50 JJg litre-1 in 10 and 20'Yr. ethanol respectiveJy2:l8

and detection and recognition thresholds of 0.5 and 4.9 mg litrc-1 rcspectively in 23'Y.. abv grain spiritl30, Lignin

thcrmal dcgradation products such as vinyl-, allyland ethyl guaiacols, guaiacol {2-methoxyphenol), cinnamaldchyde and related phcnolic adds contribute :;wed, smoky and ~·qJicy notes (Fig. 4)2:\8.27<~. Thc yeast enzyme ferulic acid decarboxylasc5'1 converts cell wall ferulic acid to 4-vinyl guaiacol. Thc rclatcd clove has a charactcr linked to oakincss238. Howcvcr spicy notes are common to dove, cinnamon bark oils, and other spiccsm2 and distinctions may bc difficuJt129 nccessitating spt.>eialiscd sensory training.

G.8. caramel- candy floss, Jrmclt', coffee, toast, liquorice

Cammei - sweet, bumt and notably smoky notes originate in thermal breakdown of lignins, dominaled by phenols such as guaiacol (2-mcthoxy phenol), 4-acetyl-guaiacol and syringol (2,6-dimethoxy phenol), homologues and derivatives. Thc stability of Jignin polymcrs limits their contributions to maturing spirit·B but lowcr molecular weight guaiacyl and syringyl produels are extracted in conccntrations decreasing wîth repeatcd usc. Certain flavour notcs originate in 5-hydmxymethyl-2-furfuraldchyde and hydroxymethylpyranoncs218 from ageing in frcshly charred casks. Caramel addcd to enhancc colour in blended whiskies also contains 5-hydroxymethyl-2-furfuraldehyde•00• In Bourbon whiskcy, 2-hydroxy-3-mcthyl-2-cyclopentenonc and 3-hydroxy-2-methyl-4-pyronc (maltol), with sweet and /111mf notcsl7l>.177, are important.

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Other stave pyrolysis-derived congencrs, from Maillard reaelions (Fig. 5), are furans: furfural, 2-methyl furfural and 5-hydroxyfurfural, and hctcrocyclic nitrogen compounds including pyrazincs, pyridines, thiazoles, aliphatic amines, quinolines and pyrans40,41,142,t77,210. Abundant nitrogcn compounds, e.g. methylpyrazine and 4-methyl-5-vinylthiazole, impart bumt, roasted and 111111y notes to rnalts and also contribute to flavour in whiskies. Such compounds are more abundant in char layers than in plain wood shavings or decper layers210. Concentrations in whiskies are significantly higher than odour thrcsholdstss. Pyrazincs are regarcled as ha ving pleasant flavour notcs: bunrt, toastecl, medici11al, twtty, fruity, woody and earthy2W,2~>J, but also pilt'IWiic, nutty and green. Flavour notes are cnhanced whcn methoxyl groups are present on pyrazine derivatives'~5. Unlike pyrazines, pyridines are perccived as lcss plcasant: astriugL'111, l'itter, buttery, caramel, raasted, green, eartlly, rubber.lf, and fattyl-1-1, and pwzgent, soft,mt and fisiJyMJ. Viro266 showed reducing pyridin{.>s in Finnish whiskies improved flavour. Such pyridim.>s are ionized at low pH (4.0-4.5) in matured whisky, and therefore flavour impact<; are low51>2IO.

G.9. Pn't'Îims use slll•rry, Bourbon, 1mrt, rum, brmuiy, WÎIIt'

Scotch whisky has traditionally been matured in reused sherry, Madeira and port casks that flavour spirit. Shortage of ex-sherry, replaced by ex-Bourbon, barrels3t,t64 has promoled pressure prc-treatments with whitc wine or sweet, dark sherry that incrcase final ester and sugar contents yiclding mildly flavoured whiskies164.

Other wood extractive characters

Mellowness, rotmdm.'Ss & smootlmess

Melloumess and lingerill?: aftertastes are related to changes in hydrogcn bonding in spirit during maturations, with formation of ethanol cluster structures2~1.lï7. Such clusters can be deduced from differential scanning calorimetry (Fig. 7)112 and adiabatic expansion studies under vacuum79,J74 of immature and mature whiskies. Non-volatile oakwood extracts (Fig. 7)114.177 stabilise clusters, increasing mt'llowuess and rozmduess with accumumulation40,21l5.2n~>. Such nonvolatiles are monosaccharides (pentoscs and hexoscs) and aromatics from cask cell walls and glycerol216 from thermal brl'akdown of wood triglyceridl's.

Defective wood characters

G.IO. motlzba/1 paraffitl, tmplltlm, Cfll1lJJiwr G.11. musi]J- mouldy, eartlty, fusty, corkL•d G.l2. viuegary acetic, sour

Mouldy and earthy notes appear to originate in fungi and actinomycetes on malts272, defective casks198 and

(Al

~ 2

-,., Cl

V

E .... (.1 .c; -0 "'0 c: (C) w

I

~

- 100

s

s

5

4

f'l.lt urcri

wtusky

Do~tollóltC

Dost•IIJte

• d•st•lled

resodue

- 20

FIG. 7. DSC thermograms of the melting of rapidty frozen matured whisky, distillate of matured whisky and restored whisky (Nishimura, el al, 1983; reproduced with peemission from Piggott, J. R. (ed.) Flavour of Distilled Beverages: Origin and Developmellt, El lis Horwood, Chichester, p.252).

cork dosures, notably Armillaria mel/ea222.228,236,237 on corks. In wines such aroma notes are linkcd to methyl thiopyrazine, 2-acetyl piperidine and its isomer 2-acetyl tetra hydro pyridine, 1-octen-3-one (musltroom), 3-octen-1-one (musty, mouldy, earthy, mushroom)32. Musty, or cork taint notes are associated with 2-methyl-îsobomeol (2-MIB (eartlzy), geosmin (mildew) and 2,4,6-trichloroanisole (2,4,6-TCA)69,2J7. Other contributors include 2,3-dicthyl-5-methylpyrazine and 2-isopropyl-3-methox ypyrazi ne (must y/mouldy) 101.124. Corks contaminated with moulds and pesticide chlorophenols 6-chlorovanillin, 4-chloroguaiacol, 4,5-dichloroguaiacol and veratrole yield chloroanisoles (e.g. 2,4,6-TCA) with corked taint and musty. These are important in tainted wines28,29,77,11S and other drinks63, originating in

woods, including shavings124. In wine, the low thresholds24H show a bimodal distribution, at 1.461 and 17.4-210 ng titre-•. Certain individuals are particularly sensitive to such flavour notes236. Before surface treatments, corks yield woody and green cork notes and after less woody and more oily from coating materials236. Off notes of microbial origin are reduced by autoclavingm.

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Gcosmin, and 2-MIB, with low delcelion thresholds (ng litre-I)Ll6 , introduced in waterl:ll-.~~u, are unstable in the acid ie environments of wint.>S and spirits.

H. Sn,eet characters

H.l. Wf)()dy-sweet: St.>e St.'Ction G

H.2. j1!1rtl/-srwet: sec section E

H.3. fruity-!Öu•eet: sec scction D

H.-l. lmttcry-sweet: Sl'C scction L

SnJeel characters are important in whisky flavour but their origins are not dcar. In 23"';, abv grain whisky, sweetness can be evokcd by diacctyl (47"'., rcspondents), maltol (38'Y.,), vanillin (28"<,), furfural (26";,), ethyl hcxanoatc (24'X,), iso-amyl acetah:- (15'~·<·), whisky lactone (10"/.,)129 • Certain assessors used only the gencric description sweef and did not specify between them which reflects either Jack of verbal ability or physical sweet properties of congeners. Vanillin is Jinked to woody-swe<'f, a lso t'tlllilla (58",:,), lo.flce (35% - toffee, carnmel, fudge and dwcolatc) and swcl'f (28%). Whisky lactone was described as conmul (84",:, of rcspondants), but has also a SWl>et almond character (llutty, 11'~ ... mar:dfltlll, 7':<. and almo11d, -l%)12'~. Nutty is rt.'lated toswed taste characterl02. 4-Vinyl guaiacol contribuh..>S swet'l

woody character to whiskies. Swt•t•t-smoky (32%) is linkcd to wood-derived phennls: SJJicy (17% - SJ'icy, mlfmes. gingt>r, clm•t' and aromaticJ, l'llllilla (13%) and woody (7'~:.). Maltol evokcd camiy .floss in +!",,, respondents, with frequent useage of rclatl>d lerms- sweet (3Y"<, - sweel and sugar:J) and caramel (35%- ctrramt'l, lmrnt sugar, toffreJ.

As for j1oral-su•t•el, gcraniol was described as flora/ (36%), let1WIIY (dtrus and <m:>lling-up liquid, 25'~;.), sce11ted so11p (21 %), but a lso swed (17'~;.)'~". As forfmity-sweet, isoamyl acelate was described as pt'ar-drop (67%). Other fruity-sweel tem\s in 23'Yc, abv gmin whisky, were lmnm111 and pear (22%)129 and !JIIltay-swet'f: discrimination of perceptions of sweel and bultery are difficult with diacetyl at 90% recognition thrcshofdl:!'l. Diacetyl was sweet to -l7% rcspondents and bufteryt tn only 31%129.

I. St11le ebaraders

1.1. cardboard -J1fll''''''' filter siJeet 1.2. mt•fallic- iuky, tiuuy, u•t.'l iron, rusty: sec the

scctinn F (jeints)

Cardl1oani-Iikt• notes generally originate in lipid oxidations of unsaturated fntty acids frum cereals or yeast metabolism 18J·2.

Lipoxygenasc oxidation of 9, 12-octndecadienoic (linoleic) and 9,12,15-octadecatrienoic (linolenic) acids yields pentanal, hexanal, nonanal, (E)-octenal, 2,4-heptadienal, (E)-2-nonenal, (E,E)-2,4-nonadicnal and 2,4-decadienal responsiblc for cantboard in hoiled potato1w.. Hexadeccnoic (palmitoleic) acid autoxidation

yil•lds (E)- and (Z)-2-nonenal and (E)-2-octanal with l'tlrdl1oard notes in butter oi!277. (E)-2-nonenal in 23% abv grain whisky was described as cardl;oard with detection and recognitiun thrcsholds of 3 and 8 J.tg litre-1, respcctivcJyDu.

J. SttlJ1Imry characters

J.1. stagum1t st•wa, dmi11s,fou/ water, rclfl!'ll n•gl'ftlble }.2. mmty- ymsty, Marmilc, rotfeil e:.;g 1 .3. vesetable t um ip, polafo, cooked veg!'lable

(swcetcom, boiled ca/Jl~t~ge> jA. sow·- piekled OllÎOII, garlic J.5. gassy tmt>11 gas, llllml match, acrid J .6. ru/llwry - tyrL'/trtbes, penálemser, plastic

Sulphur compounds are important sourees of offflavours reducing spirit qualityïtd33.153. although low concentrations in beers enhance acceptabilityll'. Water dilutions enhanccd flavour impact through hydrophobicity, although such volatility is supprcssed by wood-derived congencrs2n7. In lagers, dimethyl (DMS) and diethyl sulphide have low thresholds at 30-50 and 0.4 J.lg litre-1, n.•specth·cly, and thiols at <2 J.lg litre-1 7.1S.I"'•. In beer DMS above 100 J.lg litre-1 imparts Cl'IOked swed-com. SJ'ÎC!f and maltynx or Mackcurraut-/ikt·ï notes; at lower conccntrations flavour impacts are not significantï. In lagers, ethanethiol evokes strongcr gunpowder and acrüf notes 1 :!.'~. In 23% grain whisky deleetion and recognition lhresholds of dimethyl trisulphide (DMTS) wcre -l and 20 J.lg litre-1, rcspt•ctiveJyDo, and 3-6 J.lg litrc-1 rn. In beer nssociated flavour notes are sar/ie (onion, cabbage), drai11s and (slmck) nmtcl/128 and thresholds for H25 are 6 J.Lg litre-t '12. In grain whisky perceptions were ru/JlJery (21% respondent), sour (21 %) and gassy (15'~<.)12". Low molecular weight sulphur congeners confer ligltt and m·ut mJn:l characlers, medium as ~~~lttly bitter and roasfe•i ti11ge and higher as hem'!!· Mealy, lmmt and tlliamine-like attributcs are associated with methyl-(2-methyl-3-furyl)disulphides (MMFD), bis(2-mcthyl-3-furyl)-disulphides, and methyl (2-methyl-3-furyl)-sulphides and 2,5· dimethyl-3-mcthyldithiofuran. The important congener MMFD, present in grain and malt whiskics, has low thrcsholds of 0.005 J.lg litre-1 in rectified and 0.10 J.lg litrc-1

in grain spirit::!i. Othcr compounds derivcd from thiamine and amino acids also have low thrcsholds, <1 J.l8 litrc-1, and are important in roastcd coffce~"0 and yeast extracts'\

Barley amino amino acids (cysteine, mcthionine) yicld sulphur compounds (e.g. DMDS and DMTS) but in the absence of cystC'ine, DMDS, DMTS and mcthional are still formed during distillation71l possibly from thermally degradation of yeast mctabolic produels such as Smethyl-methioninc through Strecker degradation to methional (Fig. 5) and mcthanethioF~>. Dimethyl disulphidc (DMDS) and trisulphide (DMTS) in new spirit are linearly correlated with wash methional

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Origins of Flavour in Wlliskies and a Revised Flavour Wlteel: a Review Volume 107, No. 5, 2001

although DMTS concentration can be modulated in still operation76,211. Malathion used for pest control on barley might influence sulphur congener concentrations, but was reported to have no influencc on final spirit256.

Addition of rock sulphur or gaseous sulphur dioxide (502) during malt kilning redttees nitrosodimcthylamine (NOMA) level through rcadions between barlcy amines (espedally hordeins in thc rootlet) and fuel N02. Most nitrosamines are unstablc, cv aporating before thc kilning 'break point'. Formation of NOMA is reduced by prior rootlet removal but influcnced by hordein contcnt2.W. Sulphur dioxide at 10-30 mg litre-1 also reduces malt microbial loads11,72,2.15 and Iighteos colour. Wort pH is influenced by concentrations of so2 and sulphuric acid with effects on polysaccharide, glyco-proteins and glycolipid hydrolysis and wort concentrations of protein, n-amino nitrogen, lipids and fatty acids23.J.

Malt yields DMS from S-mcthyl-methionine (SMM), absent from barley grain but increasing during germination2U. Temperafure and moisture levels in barley at kilning influencc conversion of SMM to DMS, with a boiling point of 38"C. Although evaporating during kilning and mashing, DMS is oxidised to dimethyl sulphoxide (DMSO) and dimethyl sulphur dioxide (DMS02)7.76. Otl1er sulphur congeners formcd in mashing include carbonyl and hydragen sulphides, methanethiol, carbon disulphide, sulphur dioxide and DMS223.

In fermentation, DMSO is reduced to DMS by sulphydryl compounds during the fermentation. Anaerobic bacteria (EIIterobncteriaceae) in eertaio washes also produce DMS from DMSQ282. Yeast autolysis yields DMDS, DMTS and certain other sulphur congenersl8,21l,244 at concentrations rclated to duration and intensity of wort heating. Yeast malie and citric acids138 promote hydrogen sulphide and sulphurcontaining compounds secretion by Jactic acid bacteria (Lactobacillus brevis, and L. fermentum)6,13s. Yeast metabolism also has a role, with storage at 5°C yielding less sulphur congeners than 20°CJ62. Whisky mashes are susceptable to yeast infections, producing sulphides and further roetabolie products (e.g. ethancthiol) through hydrogen sulphide reactions with ethanoJIB. Strecker degradations (Fig. 5) of cysteine with diketone yield hydrogen sulphide (H2S) during fermentation, converted to ethanethiol and diethyl disulphide during distillation244. Such H2S (typically at 9 mg titre-I) interacts with residual maltotriose (0.8-1.4 mM) during distillation, yielding DMDS from methionine independent of the prescncc of copper ions78. Notes from H 2S were rotteu-egg at high concentrations (ca 140 11g litre-1)128 and yeasty at 50 J.tg litre-1 258. Supply of oxygen at distillation has little influence on sulphur compound formation as foam and carbon dioxide reptace air in wash headspaces7B.

Copper interacts wîth sulphur compoundsl33 and reaction with copper ions is regarcled as essential for producing clean spirit173,273. Copper ions accumulale during wash distillation reaching 15 mg litre-1 78,213.

Cupric ions react with methional to produce DMDS, converled to othcr compounds as distillation progresses7s. As conversion is faster than formation78, total DMDS concentrations in spirit are reduced.

Copper sulphate removes volatile sulphur congeners as non-volatile copper sulphides and mercaptides82. Still deposits contain coppcr cyanides, thiocyanates, oxides and sulphatesl.JO. This behaviour may be important for understanding spirit quality82. Thiols react with surface copper oxide to form copper thiolates that in excess form complexes becoming self-assembled Iayers, with chcmisorptionl09, Thiolate layers react with congeners (e.g. thiophene) influencing sensory qualityS2. However, chcmisorbed thiol is limited ( <4% of offered thiol concentration)Hl9. Distilling removes most sulphur compounds espedally in predistillate (heads) and feint (tail) fractions: a copper still removed 70% dimethyl disulphide (DMDS) more than glasst6,249 with similar findings reported for rum7o. For DMOSt53, however, glass distillation has been reported to show a ten-fold reduction over copper. Copper distillation also increases concentrations of other congeners: aldehydes, higher akohols and esters but not carboxylic acidst7o. The consensus is that copper distillation reduces sulphur congeners and positively influences sensory quality.

During maturation, oxidation of DMS to dimethylsulphoxide (DMSO) and dimethyl sulphur dioxide (DMSOz) continues: 50% of DMS was oxidized to DMSO and DMS02 after 96 h in a new cask76. This was largely effected by the charcoal, and gallic acid was less effective. After 12 months, whisky DMS contents were low and a function of maturation parameters76 and DMTS contents decreased more slowlyt33,153. Ratios of DMDS/DMTS form maturity indicators (30 for new-filling, 15 after 3 years133. Either OMDS evaporates76 or is converted to DMTS until concentrations fall below flavour thresholdsl33). Sulphur compounds- particularly, thiophcnes and polysulphides - can also differentiate products. Cask surface to volume ratios influence low molecular weight sulphur congener concentrations (DMS and DMDS) but not those of low-volatility aromatic sulphur compounds such as thiophene and thiazole153, Addition of oak wood (chips) and air reduces sulphur congeners notably methionyl acetate and ethyl methionate176.

K. Cheesy characters

KJ. rnucid 'sickly sour', baby vomit, oxidized fat K.2. sweaty o/d trainer/soek, musky, piggery

Bactcrial action (C/ostridin) yields n-butyric acid and ethyl butyrate26 with rancid (sickly) sour notes at low

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Volume 107, No. 5, 2001 Origins of Flavour i11 WIIÏskies muf a Revised Flavour Wheel: a Review

mashing temperatures or if wash stands in cast iron vesselsts9. Propionic, isa-butyric and iso-valeric acids have similar characters in whisky and are abundant in rum and brandyl82. In whisky iso-valeric acid, present in concentrations related to yeast and fermcntation conditions, dominatesiB2.

Rm1cio, a Cognac character reminiscent of musty walnuts, can be confused with mncid in whiskies. This ranch> character, indicating an old, well-ston~d cognac increasing with age in parallel with fineness and mellow/less24. The gradually acquired ranch> is from hydralysis of fatty acid esters with oxidation to thc kctones147: 2-heptanonc, 2-nonanone, 2-undecanone and 2-tridecanone. Concentrations are functions of peroxidases and cask volume264. Long chain aldehydes, methyl ketones (C7, ~ and C11 ), glyoxal and methyl glyoxal are related to ra11cio characters in old wine-spirits (e.g. Armagnac, Cognac)l9,264,265. Glyoxal is present in whisky, but at concentrations too low to be quantificd212 and Ra11cio character has notbeen explicitly idcntified. Bulterf rancio notes in winelS are related to N-(3-methylthiopropyl) acetamide and 3-methylthiopropionic acid from methionol.

L. Oily characters

L.l. soapy- waxy, wzscented soap, detergent, damp lmmdry; sec section F ifeiuts)

L.2. buttery- creamy, toffee, butterscotc/1 L.3. lubricant - mineral oi/ L.4. Jat - fatty, greasy, fisll oil, castor oil

Buttery charactcrs are related to diacctyl (2,3-butanedione), an off-notc in lagers254. Diacetyl and 3-hydroxy butanone are also important in wines, cspt.-cially sweet Sherries150,279. Diacetyl is produccd by citrate-metabolising Jactic acid bacteria8,253 and in yeast fermentations formed from a-acetolactate and mctabolised to acetoin. Yeast metabolism can be manipulated to produce acetoin directly from a-acetolactate26ï, In whisky nosing, diacetyl has a detection threshold of 0.02 mg litrc-1, a recognition of 0.04, and in tasting is 0.2 mg titre-I 127.267. Fermcntation oxygen influcnces spirit diacetyl contcnt22.

T. Primary taste

T.l. sweet

Oak maturation influcnccs time intensity factors (maximum intensity and duration) of sweet taste in sugar cane spirit (cachaça)25. After 2 years there was little incrcase in peak intensity but a substantial increase in duration. Spirit changes can thercfore influence perception of sweet character209. In whisky, congeners conferring sweet are extracted from wood largely within 3 years216.226. Glycerol primarily from wood triglycerides216

may also be generaled by trans-esterification of triglycerides and ethanol, yielding fatty acid ethyl t.>sters

and free glycerol218. In Bourbon whlskies stave hcmicelluloses and acid-catalysed hydralysis of tannins yield monosaccharides (arabinose, glucose, xylose, galactose and rhamnose)226. Concentrations of most sugars increase in the early stages of wood maturation, but fructose and glycerol are still formed late in maturation (Fig. 8). Glucose, fructose, proto-quercitol and arabinose are reported the most abundant in whiskies30,1!>5,181 with similaritics in saccharide compositions in 12-month Scotch and Irish whisky distillates: Bourbons contained less arabinose and more xylose through ncwwood extractionsl81. Bourbon spirit had greater total sugar contents than Scotch and Irish (Table IV), and quantitative differences may increase with age. Such concentrations of sugar in retailed whiskies are thought too low (Table IV) to induce sweet138,209 characters- detection threshold is approxîmately 5 g litre-1 in water. Ethanol, enhancing water structures through hydrophobic effects75,:t10, decreased sweetness intensity and persistenee in sugars%. In summary it is believed that sugars make lcsser contributions to flavour209 than other congeners such as vanillin, whisky lactone and maltoL Fruity, woody, flora/ and buttery characters enhances sweet characters in whisky209. Howevcr, Swan has suggested products of hemicellulose degradations add fudgey and caramel notes and colour to whisky, those of cellulose have little impact (Swan. J., unpublished).

T.2. so11r

Wood-derived acids and esters in whiskies are thought to influence flavour littleiSl. Wood-derived non-volatile congeners in matured whiskies include: oxalic, fumaric, sucdnic, methyl- and methoxy succinic, mesaconnic, adipic, phthalic, azelaic, sebacic and trimethybenzoic acids. Ncw distil1ate has a fixed addity of zero134 but over 12 months the extraction of acids, oxidations of ethanol and other congeners and other reaelions produce an addic environment13.J. A typkal matured whisky is pH <4.556.

T.3. sally

This charactcr, often adopted in whisky flavour evaluations, is of uncertain origin. lt is possibly associated with peat bogs close toa sea, saturated with marine spray and seawccd relicsJ.II. Coastal warehousing with permcation by damp salty air could produce salty charactersl41.

T.4. bitter: sec section M (moutheffect) -astringent

M. Mouth effect (moutllfeel)

M.l. warming- alcollolic, bum, fiery M.2. coating- oily, creamy feeling

A highly intense bitbzg sensation, described as bumiug, can încrease to a pain sensation. Buming also includes a warm sens~tionlll2.

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I 5 -"' liJ '-.~ -0 0 '-a.

10 0 0

'-OJ a. 0.0 -c

Xylose Fructose Glycerol Galactose 0 s ;::. . t'O '-~

c liJ u c 0 u

Age (years)

FIG. 8. Changes in sugars and glycerol during maturation (R~azin, 1981, reproduced with permission from Amcricau Joumal of Enology a11d Viticttltttre, 32, 284).

TABLE IV. Contents (mg litre·•) of sugars insome whiski1.>s.

Sugar Scotch (6 y) Scotch ( 12 y) Irish Bourbon

Glucose 106.0- 248.3 170.5-181.6 114.1 85.1

Proto-qucrcitol 10.4- 16.5 28.9- 34.4 8.6 90.9

Arabinase 14.4- 21.1 35.6- 42.9 12.4 82.5

Xylose 6.2- 8.2 18.4-20.1 5.3 82.1

Mannose 31.3 - 69.6 35.3 - 35.5 6.8 19.2

Galactose 1.5- 3.0 5.4- 6~2 0.7 16.2

Rhamnose 1.5 - 2.2 4.0-4.5 1.5 10.6

lnositol 1.2 - 2.2 4.4 - 5.6 1.2 13.1

(Nykänen et al .. 1984; reproduced with permission from Hel.~inki FmmJaticmfur Biutec:hnic:al & JnJw;triul F ermentation Re.wmrd1. 1984. 141)

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Volume Wi, No. 5, 2001 Origins t~{ Flm.'OIIr in Wltiskit•s tmd a Rt•vised Flavour Wltt•t•l: a Rtrvit•w

In many products the term frt'fl11ti1u•ss is important for appearance, flavour or tcxtu~>-~. In whisky, understanding of thc character is limited but rclatcd to mouthfcellll3 and also described as 'Iength in mouth'!ll, Perception could be relatcd to tllickness, smaolfmt•ssll5 and fitlty moutlifeef39

and is closcly related to lmllay (diacctyl) in many fonds and whiskyll1.''7.111.128,1M. In whisky, consumcrs to represenl maturity may use this character associated with: smootlmt•ss, rotmdness, bt>dy. ridmess and mellownessH5. Ethyllactnte, f rom esterification of Jactic acid of bacterial origins, is reported linked to aemuy character27'l, In spirit, ethyl Jaclate yidd is relatcd to length of fcrmentationlli,. Howe\'er, n..•lationships between creamy and smootlmt•ss appear to ... -tiffcr.

M.3. astringt'nt- drying, furry, powdery

Astringml is a trigeminal tactile scnsalion related to behaviour of the epithelium on exposure to tannins yiclding on ingestion tirying, rougltiug, 1mckaing or timwing scnsations126 • Such scnsations, from binding of tannin to salivary proteins, mucopolysaccharides or directly to oral epithelia, rcduce the lubricating effects of saliva, promoting mug/mess, particularly following repeatcd cxposurel:!6.

Such flavour componcnts, absent from ncw spirit, accumulate through extraction of wood and by oxidation processes. Wood·derived tannic substances contributc bitter and astriugt'llf character, but add colour and delimll' fragrauce to whiskiesló5.

These watcr-soluble plant polyphenols, are commonly divided into the condensed - dcrivativcs of flavonals -and hydrolysablc tannins (gallotannins and ellagitannins). Ellagitannins, monosaccharide polyols (normally D· glucose) with hydroxyl groups esterifk-d by either gallic or hcxahydroxydiphenic (HHDP) acids, are hydrolysed either enzymically or in acid or base conditions, to frcc gallic or HHDP acid, thc latter Jactonizing to cllagic acidl~>5. Polyphenols from white oak heartwood indude gallic and cllagic acids, gallo- and cllagHannins3ï,177. Such tannins oxidise slowly and polymerisc as heart wood agcs, rcdudng solubilityl65 and pcrccptions of astringency as in ripening fruitHH. The effect is thought to be-ti: promotion of ethanol oxidation to acetaldehyde and diethyl acetal; and formation of esters from acids (t•.g. acetic acid) and alcohols. Tannic substances assist char 1ayers in removal of distillate sulphklcsJ~.u,:; and nitrogcn compoundsï6. Ellagitannins, abundant in raw wood, in exn.>ss confer undcsirable flavour charactcrscontents can be reduced by hot water extraelions or charring73,142. Ellagitannin hydrolyses to gallic and ellagic acids, absent fmm new distillatclM but pn.>scnl in maturing malt whiskics after 2 ycars226 • Wine spirit extraction of gallic acid is maximal after heat treatml•nt of wood at ca. 165°C151. Gallic and ellagic acid contcnts of spirit form indicators of maturationli7 but their influcnces on whisky flavour are nol clcarly undcrstood 165.

FUTURE RESEARCH

This review treats flavour attributes of whiskics, defined in a rcviscd flavour wheel, as if perccived at a ltnified time point. However pcrceptions on ingcstion of whisky form n temporal progrcssion and thc limitcd understanding of time intcnsity features suggcst a fertilc Mea for research.

Scnsory assessors and panel are not analytica! inslruments. In assessing products, psychophysics and psychology intcrplay. Definition and numberof attributes and scale uscage are important in assessor training; order and scssion effects should be considcrcd in industrial sensory panel assessments.

Undcrstanding of the fundamental nature of whisky maturation is a lso rcquired. Little is known a bout dctailcd physical structures of the aqueous ethanolliquid phases of new distillates and matur~.>d whiskies. High·rcsolution analysis stratcgies, such as neutron scatter, combined with headspace congener studies wiJl contribute to an undcrstanding of sensory ~.1uality that will benefit whisky distillers.

Howevcr, perhaps greatest priority should be given to understanding perceptions of flavour charactcr in whiskies. Products are perceived holistically by consumcrs but analysed by scnsory assessors through quantifications of deconstructed attributcs. Study of relationships between these two, fundamentally different, forms of mental processing is an urgent rcquirement for onderstanding whisky quality.

CONCLUSIONS

On drinking a glass of whisky, consumers employ pattem recognition processes, using scnsory data to dcvelop a holistic mental image in spccific regions of the brain. Flavour recognition involves matching of information from long·term, short·term and sensory memories. Whisky maturation influenccs volatile congener relcase into headspaces through modifications of spirit liquid phases, and agglomerates. Complex changes in congener partitioning replace immature notes in new distillates with matured whisky characters.

The reviscd flavour wht.>cl specifies a vocabulary that dcfines consensus deconstructed attributes of whiskies to meet industrial needs. Each attributc is demonstrabie by a flavour standard and terms suitablc for training of sensory assessors for quality assurance, new product d ... ·vclopment and similar purposcs.

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