BEER VOLATILE COMPOUNDS IN DEPENDENCE
ON YEAST STRAIN USED FOR FERMENTATION
Daniela Šmogrovičová
Department of Biochemical Technology
Institute of Biotechnology and Food Science
e-mail: [email protected]
2
Beer flavour
Result of a complex combination of components
malt, hops, water
yeast metabolites – by-products during fermentation and maturation make an important contribution to flavour
3
Yeast metabolites in beer
The most notable metabolites are:
ethanol and carbon dioxide
a large number of other sensory active compounds
diacetyl
acetaldehyde
higher alcohols
esters
4
Yeast and flavour of beer
Brewer’s yeast
bottom-fermenting
top-fermenting
Yeast strains – their own character – impart different aroma and flavour characteristics to beer
may vary in which complex sugars they can ferment
how high their alcohol tolerance is
Fermentation temperature and flavour of beer
Bottom fermented beer – fermentation at low temperatures
Higher temperatures
increase the rate of yeast metabolism and fermentation
influence each biochemical reaction of yeast metabolism, changing the balance of flavour compounds
Temperatures above 14°C results in a product with
significantly poorer aroma and taste
The goal of this study
To identify the factors that impact the formation of
sensory active metabolites in beer
Their role in sensory assessment
The influence of
yeast strain – industrially used
top-fermenting
bottom-fermenting
fermentation temperature
wort gravity
Studied compounds
Acetaldehyde
Higher alcohols
propanol, 1-butanol, 2-butanol, iso-butanol, 1-pentanol, 3-
methyl-1-butanol (iso-amyl alcohol), hexanol
Esters
acetates – methyl, ethyl, butyl, iso-butyl, iso-amyl, hexyl,
2-phenylethyl
ethyl butyrate, ethyl iso-valerate, ethyl hexanoate, ethyl
octanoate
Acetaldehyde
the most important aldehyde of beer
in beers usually lies in the range 2–20 mg/l
at concentrations of 20–25 mg/l acetaldehyde
causes green apple flavour, green vegetation or
vegetable flavour
in levels over 150 mg/l may cause an aldehydic
character of high astringency values
Acetaldehyde formation
intermediate from carbohydrates to ethanol
formation occurs during the first three days of
fermentation
permanent reduction during maturation and aging
depends on yeast strain
Higher alcohols
propanol and 2-methylpropanol (iso-butanol) – rough flavours, harshness of beer
butanol, 2-butanol – alcoholic perception, general alcohol warming sensation in the mouth
2-methylbutanol (amyl alcohol) – fruity flavour in threshold conc. of 50 mg/l
3-methylbutanol (iso-amyl alcohol) – burning disagreeable odour in conc. higher than 1 mg/l
pentanol (amyl alcohol) – cough-exciting odour and burning taste
hexanol – odour of freshly mown grass
phenylethanol – sweet or rose flavour
Higher alcohols formation
arises through decarboxylation and reduction of the
appropriate -keto acid
keto-acids are produced via catabolic or anabolic
pathways, depending on the concentration of amino
acids available
either by transamination of an amino acid present in
the medium (Ehrlich pathway)
or from the anabolic pathway from pyruvate
Esters ethyl acetate – fruity sweet, appr. 1/3 of all esters in beers
methyl acetate – glues, nail polish remover
butyl, iso-butyl, iso-amyl, hexyl, 2-phenylethyl acetate – fruity – banana, apple, floral – rose aromas
ethyl isovalerate – pleasant aroma, fruity flavour
ethyl butyrate – pineapple flavouring, fresh orange juice
ethyl hexanoate, ethyl octanoate, ethyl decanoate – apple
Esters formation
can be formed by a simple condensation reaction between an alcohol and a carboxylic acid, although the rate of this reaction is too slow
the condensation reaction between a higher alcohol and an activated acyl-coenzyme A (acyl-CoA) – catalysed by alcohol acyltransferases
no direct relationship between yeast growth and ester synthesis
Higher alcohols-to-esters ratio
the flavour of a beer depends not
only on the content of its
compounds but more on their ratio
the optimum higher alcohols-to-
esters ratio for lagers according to
literature is from
4.1 to 4.7:1
Results
Concentrations of the studied compounds were proportional to the
wort gravity
The exception was acetaldehyde – its concentration in beers of
gravity 10 °P was similar than that in beers of gravity 12 °P, or
slightly higher
0
1
2
3
4
10 °P wort 12 °P wort
co
nc
en
tra
tio
n (µ
g/l
)
ethyl butyrate
pentanol
acetaldehyde
Results
The maximum concentrations of the studied compounds were
observed in top-fermented beers due to higher fermentation
temperatures
The exceptions were butanol, butyl acetate, ethyl iso-valerate
and ethyl octanoate
0
2
4
6
8
10
12
co
nc
en
tra
tio
n (µg/l)
bottom-fermentingyeasts
top-fermentingyeasts
Results Flavour-active compounds produced by two different
bottom-fermenting yeast strains were noticeably different in
the content of:
ethyl acetate
ethyl octanoate
iso-amyl acetate
In beers of gravity 10 °P the most significant difference was in
the iso-amyl and ethyl acetate content
In beers of gravity 12 °P, the most significant differences were
observed in the ethyl octanoate production
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Differences in flavour-active compounds production by two
bottom-fermenting yeast strains, wort gravity 10 °P
0
5
10
15
20
25
30
35
40
45
50
co
nc
en
tra
tio
n (µg/l)
strain W34,wort 10 °P
strain 2, wort10 °P
19
Differences in flavour-active compounds production by two
bottom-fermenting yeast strains, wort gravity 12 °P
0
20
40
60
80
100
120
140
co
nce
ntr
ati
on
(µ
g/l
)
strain W34,wort 12 °P
strain 2, wort12 °P
20
Aromatic profile of top fermented beers using different yeast strains
alcohol
banana
pineappleapple
pear
strain I.S.C 57, wort 10 °P
strain I.S.C 57, wort 12 °P
alcohol
banana
pineappleapple
pear
strain I.S.C. 46, wort 10 °P
strain I.S.C. 46, wort 12 °P
Aromatic profile of bottom fermented beers using different yeast strains
alcohol
banana
pineappleapple
pear
strain 2, wort 10 °P
strain 2, wort 12 °P
alcohol
banana
pineappleapple
pear
strain W34, wort 10 °P
strain W34, wort 12 °P
Conclusion
The concentrations of the studied compounds were
proportional to the wort gravity, the exception was
acetaldehyde
The maximum concentrations of the studied compounds were
observed in top-fermented beers due to higher fermentation
temperatures, with exceptions of ethyl iso-valerate, butyl
acetate, butanol and ethyl octanoate
Flavour-active compounds produced by two different
industrially used yeast strains were noticeably different
Thank you for your attention !
