ORIGINAL PAPER

Effect of Process Parameters on Partial Dealcoholizationof Wine by Osmotic Distillation

Loredana Liguori & Paola Russo & Donatella Albanese &

Marisa Di Matteo

Received: 18 February 2012 /Accepted: 9 April 2012# Springer Science+Business Media, LLC 2012

Abstract The effectiveness of the osmotic distillation pro-cess for partial dealcoholization of wine was investigated inthis work. The dealcoholization process was performedusing a hollow fibre membrane module and process param-eters, such as hydrodynamic conditions, number of cycles,temperature and ethanol content of feed solution were in-vestigated. Then the partial dealcoholization of Aglianicored wine was carried out up to 2 %vol and the chemico-physical properties evaluated and compared with the initialwine. No significant differences (p<0.05) in total volatileacidity, colour, total polyphenols and organic acids content,between Aglianico and dealcoholized wine were found.Empirical correlations available in the literature for calcula-tion of ethanol mass transfer coefficient seems able to de-scribe with reasonable agreement the effect of operatingconditions of the dealcoholization process.

Keywords Wine . Dealcoholization . Osmotic distillation .

Membrane process . Hollow fibre membrane

Nomenclaturea ethanol activity (−)d diameter (metre)k mass transfer coefficient (metre per second)C concentration (percent volume)D diffusion coefficient (square metre per second)J ethanol flux (gram per square metre per second)K mass transfer coefficient (gram per square metre per

second per Pascal)K0 Dusty-gas model constant (metre)

L module total length (metre)M molecular weight (kilogram per kilomole)Psat saturation pressure (Pascal)Q flow rate (millilitre per minute)R mass transfer resistance (Pascal second per gram)Rg ideal gas constant (Joules per mole per °C)Re Reynolds number (−)Sc Schmidt number (−)Sh Sherwood number (−)T temperature (°C)X ethanol molar fraction (−)

Greek lettersδ membrane thickness (metre)ε membrane porosity (−)γ activity coefficient (−)μ fluid viscosity (Pascal second)ρ fluid density (kilogram per cubic metre)τ membrane tortuosity (−)ϕ packing density (−)

Subscriptsexp experimentalf feed sideh hydraulick Knudsenlm logarithmic meanm membranem-air molecular-airov overallp pores stripping side

SuperscriptsEtOH ethanol

L. Liguori : P. Russo (*) :D. Albanese :M. Di MatteoDepartment of Industrial Engineering, University of Salerno,via Ponte don Melillo,84084 Fisciano, SA, Italye-mail: parusso@unisa.it

Food Bioprocess TechnolDOI 10.1007/s11947-012-0856-z

Introduction

In recent years, it is common to find high alcohol content winesdue to the climatic trends of last harvests and the research ofadvantages stages of ripening of the grapes to obtain flavourfulwines. The growing interest of the wine industry to reduce theethyl alcohol concentration in wines has led to an increasingattention to dealcoholization techniques. In this context, theEuropean Commission (Commission Regulation (EC) No606/2009) introduced the partial dealcoholization of wine byphysical separation techniques as an oenological practice per-formed for the reduction of not more than 2 %vol of the actualalcoholic strength. Moreover, the requirements of regulationlay down that wines treated must have no organoleptic faultsand must be suitable for direct human consumption.

Different methods have been proposed to produce low-alcohol content beverages from wine by reducing fermentablesugar concentration inmust and so the amount of ethyl alcoholproduced by yeasts; or, as an alternative, by physically remov-ing alcohol from wine. With reference to the latter, in theliterature, various techniques have been investigated to pro-duce low-alcoholic beverages: distillation under vacuum(Gomez-Plaza et al. 1999), spinning cone column (Belisario-Sanchez et al. 2009; 2011), extraction by organic solvents orsupercritical carbon dioxide (Macedo et al. 2008; Medina andMartinez 1997), membrane processes such as reverse osmosis(Labanda et al. 2009; Pilipovik and Riverol 2005; Catarino etal. 2007), pervaporation (Takacs et al. 2007), diafiltration(Catarino and Mendes 2011) and osmotic distillation (Dibanet al. 2008; Varavuth et al. 2009; Fragrasso et al. 2010).Among them, the osmotic distillation has been introduced asa promising technology to reduce the ethanol content in thealcoholic beverages with minimal changes to the sensorialproperties of the product (Hogan et al. 1998).

Osmotic distillation is a technique based on the use of amembrane contactor where the microporous hydrophobicmembrane separates two aqueous solutions and, due to itshydrophobicity, prevents penetration of aqueous solutions intothe pores. The membrane thereby acts as a vapour gap betweentwo liquid phases: membrane surface is in contact with aconcentrated solution (feed) on one side and a dilute aqueoussolution (stripper agent) on the other one. Therefore, the sepa-ration mechanism of a volatile component from a solution isdependent on the difference in activity or in vapour pressurebetween the feed and stripping solutions, where the volatilecomponent is soluble or miscible. For wine dealcoholization,ethanol is selectively removed fromwine usingwater as stripperagent. Moreover, the operating temperature (room temperature)and pressure (atmospheric) of the process avoid the thermaldamage of components and of aroma, the loss of flavour andassure low energy consumption (Hogan et al. 1998).

Hogan et al. (1998) described as primary application ofthe osmotic distillation, the ethanol removal from fermented

beverages such as wine or beer. In particular, they suggestedthat a reduction of wine alcohol content up to 6 %vol attemperature of 10–20 °C, by water as stripping agent,caused minimal losses in flavour and fragrance components.Of course, the process permits removal of nearly all theethanol, if that is desired.

Diban et al. (2008) investigated the application of theosmotic distillation to the partial dealcoholization of wineusing synthetic wine solutions. They found that the initialethanol concentration (in the range of 10–13 %vol) in thesolution insignificantly affects the alcohol reduction, reachedat the same process conditions. Moreover, they observed anincreased alcohol transfer in the stripping phase when alower feed flow rate was used, because of higher retentiontime of the feed solution into the module. They evaluatedand modelled ethanol and aroma compounds transfer forfeed and stripping sides, showing that the major contributionto the transport resistance was due to the membrane one.Finally, they showed that a partial dealcoholization (reduc-tion of 2 %vol) of Merlot wine gave acceptable aroma losseswithout a perceptible depletion of the product quality.

Varavuth et al. (2009) compared the performance of theosmotic distillation dealcoholization process using differenttype of stripping agents by changing the flow rates of feedand stripping solutions and temperature. They concluded thatwater is the best suitable stripper providing higher ethanol fluxand lower counter transport of water due to the low wateractivity differences between the two sides of membrane sur-face. The results of their study showed that the ethanol flux andethanol removal performance were enhanced, increasing feedand stripping solution rates and operating temperatures. Butaroma components were significantly lost during the process.

In all the previous studies the authors investigated the deal-coholization performance of the osmotic distillation processusing a single type of membrane. Different membrane moduleconfigurations are currently available with various applicationssuch as wastewater treatment, volatile organic compoundsremoval from waste gas, dealcoholization, fermentation,pharmaceuticals, carbonation of beverages, protein extraction(Stanojevic et al. 2003). Hollow fibres membrane containedin a cylindrical housing was currently used for wine deal-coholization process (Varavuth et al. 2009; Diban et al. 2008).

However, in our knowledge, none of these studies inves-tigated the effect of partial dealcoholization on the chemico-physical properties of wine. In order to fulfill this gap, thepresent work was focused on the analysis of the mainparameters which influence the wine quality.

To this aim, the effect of process parameters on partial deal-coholization of wine by osmotic distillationwas investigated. Inparticular, the dealcoholization of hydroalcoholic solutions wascarried out changing feed and stripping stream flow rates,number of cycles, temperature and ethanol content of feedsolution. Once the best operating conditions were identified,

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the partial dealcoholization of Aglianico red wine was carriedout and possible changes in the chemico-physical propertieswere evaluated. The capability of ethanol mass transfer coeffi-cient, calculated by means of correlations available in theliterature, to predict experimental results was analysed.

Materials and Methods

Materials

The characteristics of membrane module used for dealcoho-lization tests were reported in Table 1. Ethyl alcohol at 99 %grade was purchased from Baker (J.T. Baker, Milan, Italy).Aglianico wine (12.5 %vol) purchased from a local marketwas used. All reagents used for chemical analyses wereanalytical grade by Sigma Aldrich.

Experimental Setup

The rectangular 0.5×1 Micromodule (Liqui-cel; Table 1)was used to setup a lab scale plant for dealcoholization tests.The plant was schematically shown in Fig. 1. Feed (hydro-alcoholic solution or wine) and stripping (water) streamswere fed to the module by peristaltic pumps (Miniplus,Gilson). Hydroalcoholic solutions and distilled water flowedin cross flow direction in the shell and tube side, respective-ly. The temperature of both feed and stripping streams wascontrolled by a thermostatic water bath and the temperaturesof retentate (dealcoholized solution) and permeate (waterenriched in ethanol) were monitored by K-type thermocou-ples. Feed pressure was measured by a manometer. Thedealcoholization of hydroalcoholic solutions (about200 ml) was carried out in consecutive cycles; for eachcycle, the feed and stripping streams flowed through themembrane in single pass; at the end of each cycle, theretentate was collected and recycled to the membrane for

the next cycles. For wine dealcoholization tests, feed andstripping streams flowed in recycle mode.

Experimental Conditions

The effect of operating parameters (i.e. feed and strippingflow rate, temperature and alcohol content in feed stream)on ethanol removal performance of the membrane wasinvestigated. The feed (Qf) and stripping (Qs) flow rateswere changed in the range 0.6–8.6 mL/min; temperatureswere kept at 15, 20, 35 °C for both streams. Hydroalcoholicsolution concentrations (Cf) ranged from 10 to 15 %vol.

In wine dealcoholization tests, wine and water, at 20 °C,flowed into the membrane at 1.2 and 2.4 mL/min respec-tively. The volume of both streams was 500 mL. The testlasted 8 h. Table 2 reports an overview of experimentalconditions in the tests.

Chemical Analyses

Aglianico wine and dealcoholized wine samples were char-acterized in terms of: alcohol, total polyphenols and organicacids content, total and volatile acidity and colour. Alcoholcontent, total and volatile acidity, organic acids amount wereevaluated using the OIV methods (International Organisa-tion of Vine and Wine methods, 2012): total and volatileacidity were expressed as grams of tartaric acid and aceticacid content (gram per litre), respectively.

The total phenolic content of Aglianico wine and deal-coholized wine was determined according to Singleton andRossi (1965) and expressed as gallic acid equivalents (GAE;milligrams per litre).

Colour parameters (colour intensity (CI), tonality (To),optical density (OD) at 420, 520, 620 nm of wine anddealcoholized samples were investigated according toGlories (1984) and calculated as follows:

CI ¼ OD420þ OD520þ OD620 ð1Þ

OD420 %ð Þ ¼ OD420

CI� 100 ð2Þ

OD520 %ð Þ ¼ OD520

CI� 100 ð3Þ

OD620 %ð Þ ¼ OD420

CI� 100 ð4Þ

The spectrophotometric measurements were made on un-diluted wine samples using a 1 mm optical path. Absorbanceswere measured by Perkin Elmer UV/VIS Spectrometer,

Table 1 Characteristics of the micromodule 0.5×1 Liqui-Cel; Mem-brana, Polypore Company

Membrane Celgard X 50

Material PP

Pore size (μm) 0.06

Porosity (%) 40

Surface area (cm2) 100

Active length (cm) 1.5

Shell side (mL) 2.7

Number of tubes 700

Tube type Hollow fibre

Tube inner diameter (μm) 200

Tube outer diameter (μm) 300

Maximum flow rate (L/h) 1.8

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equipped with Lambda Bio 40 software. Analyses were madein triplicate.

Statistical Analysis

Dealcoholization tests were carried out in triplicate andmean values and standard deviation values were reported.Monofactorial variance analysis was used to determine

significant differences (p<0.05) between Aglianico wineand dealcoholized wine by Analysis Lab software.

Theory

Due to the hydrophobicity of the membrane, the aqueoussolution cannot enter the pores and a liquid–vapour interface

Fig. 1 Lab scale plant for osmotic distillation experiments: 1 agent stripping tank, 2 feed tank, 3 peristaltic pumps, 4 flow metres, 5 thermostaticwater bath, 6 thermocouples, 7 pressure gauge, 8 membrane, 9 permeate tank, 10 retentate tank

Table 2 Experimental conditions overview

Dealcoholization T(°C)

Cf

(% vol)Qf

(mL/min)Vf

(mL)Qs

(mL/min)No ofcycles

Flow conditions offeed and stripping agent

Hydroalcoholic solution 20 10 1.2 200 1.2, 2.4,3.6, 5.6

5 Single pass

20 10 2.4 200 2.4, 5.6, 8.6 5 Single pass

20 10 0.6, 1.2,3.6, 5.6

200 2.4 5 Single pass

20 10 1.2 200 2.4 5 Single pass

20 12.5 1.2 200 2.4 7 Single pass

20 15 1.2 200 2.4 7 Single pass

15 10 1.2 200 1.2 5 Single pass

20 10 1.2 200 1.2 5 Single pass

35 10 1.2 200 1.2 5 Single pass

15 10 1.2 200 2.4 5 Single pass

20 10 1.2 200 2.4 5 Single pass

35 10 1.2 200 2.4 5 Single pass

Wine 20 12.5 1.2 500 2.4 1 Recycle

Cf feed concentration, Qf feed stream flow rate, Qs stripping stream flow rate, T temperature, Vf feed volume

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is formed in each pore. Hence, the dealcoholization processby osmotic distillation implies evaporation of ethanol at thefeed side, which is transported by vapour diffusion throughthe membrane pores and condensed into the stripping liquidon the opposite side of the membrane (Gostoli 1999). Theethanol concentration difference between the two solutionsat membrane sides induces an ethanol vapour pressure dif-ference, which is the driving force of the ethanol flux (Alvesand Coelhoso 2004). The ethanol flux is determined byconsidering an overall resistance to mass transfer (Rov)given by three mass transfer resistances in series: (1) resis-tance in feed boundary layer (Rf), (2) membrane resistancethrough the air gaps in the membrane pores (Rm) and (3)resistance in stripping boundary layer (Rs):

Rov ¼ Rf þ Rm þ Rs ð5ÞThe resistances are inversely proportional to the local

mass transfer coefficients and are a function of the system’sgeometry. For hollow fibres system (Diban et al. 2008), theEq. 5 takes the form of:

1

AeKov¼ HEtOH

MEtOHAf kfþ 1

AlmKmþ HEtOH

MEtOHAsksð6Þ

where Kov is the overall mass transfer coefficients of theethanol; kf and ks are the mass transfer coefficient of ethanolin the boundary layers for feed and stripping side respec-tively; Km is the membrane mass transfer coefficient; HEtOH

is the partition coefficient of ethanol (assuming the same forfeed and stripping streams); MEtOH is the molecular weightof ethanol; Ae is the effective membrane contact area and Af,As, and Alm are the fibres inner, external and algorithmicmean areas, respectively. For the gas–liquid partition coef-ficient of ethanol dissolved in water, the correlation asfunction of temperature found by Warneck (2006) was used.

For membrane contactors mass transfer coefficients,expressed by the Sherwood (Sh) number, can be predictedusing correlations of the form of Eq. 7 (Ravindra Babu et al.2006). In these correlations, Sh number is a function of thedimensionless numbers of Reynolds (Re) and Schmidt (Sc)and a function of geometry f

Sh ¼ AReaScbf ðgeometryÞ ð7Þwhere A, α, and β are constants determined experimentally,Sh and Re numbers are calculated from the average linearvelocity and the hydraulic diameter coincident with the tubediameter (tube side) or based on shell cross-section (shell side).

In this work, the stripping agent flowed inside the fibresof the hollow fibre module and the feed stream in the shellside, so different forms of the Eq. 7 were used for theevaluation of the mass transfer coefficients kf and ks.

In the case of flows inside tubes (or fibres), the followingcorrelation was shown by several investigators to predict

tube side mass transfer coefficient ks with reasonableaccuracy (Gawronski & Wrzesinska 2000; Skelland 1974;Viegas et al. 1998):

Sh ¼ 1:615dhL

� �0:33

ReScð Þ0:33 ð8Þ

where dh is the hydraulic diameter and L is the fibre length.This is the Lévêque equation and it applies for laminar flowand Graetz number (Gz) larger than 400.

In the case of turbulent flow the following equation isapplied for 1<Sc<1000:

Sh ¼ 0:023Re0:8Sc0:33 ð9Þ

For shell side, empirical correlations are predominantly used(Gabelman and Hwang 1999). Recently, Thanedgunbaworn etal. (2007) reported correlations based on previous investiga-tions where the fibre bundle was assimilated to a denselypacked bed and the hydraulic diameter of the bed of fibres, inplace of the outer diameter of a single fibre as is conventionallydone, was employed. Here, for the kf, the correlation of Wick-ramasinghe et al. (1992), valid for shell side flow across thefibres, was chosen because constrains of the equation corre-spond to our experimental conditions:

Sh ¼ 0:15Re0:8Sc0:33 ð10Þ

Dusty gas model, based on the well-developed kinetictheory of gases, allows to describe the ethanol vapour trans-port through membrane pores as reported in the literature(Alves and Coelhoso 2004; Ravindra Babu et al. 2006). Inthis model, the porous medium is assumed as a group ofuniformly distributed dust particles held stationary in spaceand the molecule–pore wall and molecule–molecule colli-sions into the membrane pore are considered in the diffusionmechanism. The presence of gas–surface interactions is takeninto account by considering the dust particles as giant mole-cules. Since the osmotic process is carried out at ambienttemperature and pressure, using membranes with pore sizeusually ranging from 0.1 to 1 μm, it can be assumed that themain transport mechanisms driving the process are Knudsenand molecular diffusion (Alves and Coelhoso 2004). In thiscase, the Km of ethanol is given by the equation:

Km ¼ MEtOH

RgTd1

DEtOHk

þ 1

DEtOHm�air

� ��1

ð11Þ

where Rg is the ideal gas constant, T is the temperature, δ is themembrane thickness and DEtOH

m�air is the molecular effectivediffusivity of the ethanol in air estimated with the Fuller, Schet-tler and Giddings relation (Perry 2001) while the Knudseneffective diffusivity for ethanol,Dk

EtOH, is calculated as follows:

Food Bioprocess Technol

Tab

le3

Theorical

masstransfer

coefficientsandethano

lflux

,experimentalethano

lflux

atdifferentop

eratingcond

ition

s

T(°C)

Cf(%

vol)

Qf(m

L/m

in)

Re f

Qs(m

L/m

in)

Re s

k f(m

/s)

k s(m

/s)

Km(g/(m

2sPa))

Kov(g/(m

2sPa))

J(g/(m

2s))

J Exp(g/(m

2s))

1510

1.2

151.2

659

2.87

10−6

1.84

10−6

3.60

10−5

2.53

10−5

0.02

10.01

0

1510

1.2

152.4

1,31

92.87

10−6

2.32

10−6

3.60

10−5

2.59

10−5

0.02

10.03

2

2010

1.2

181.2

753

3.14

10−6

1.87

10−6

3.63

10−5

2.39

10−5

0.02

60.02

8

2010

1.2

182.4

1,50

53.14

10−6

2.35

10−6

3.63

10−5

2.47

10−5

0.02

70.02

9

2010

1.2

183.6

3,01

03.14

10−6

9.39

10−7

3.63

10−5

2.08

10−5

0.02

30.01

7

2010

1.2

185.6

4,51

53.14

10−6

1.30

10−6

3.63

10−5

2.24

10−5

0.02

50.01

9

2010

2.4

362.4

1,50

55.46

10−6

2.35

10−6

3.63

10−5

2.50

10−5

0.02

80.02

6

2010

2.4

365.6

4,51

55.46

10−6

1.30

10−6

3.63

10−5

2.30

10−5

0.02

50.02

2

2010

2.4

368.6

6,02

05.46

10−6

1.63

10−6

3.63

10−5

2.41

10−5

0.02

60.02

5

2010

0.6

92.4

1,50

51.80

10−6

2.35

10−6

3.63

10−5

2.35

10−5

0.02

60.02

6

2010

1.2

182.4

1,50

53.13

10−6

2.35

10−6

3.63

10−5

2.47

10−5

0.02

70.02

9

2010

3.6

732.4

1,50

59.50

10−6

2.35

10−6

3.63

10−5

2.59

10−5

0.02

80.02

6

2010

5.6

109

2.4

1,50

51.31

10−5

2.35

10−6

3.63

10−5

2.60

10−5

0.02

80.03

2

2012

.51.2

172.4

1,50

53.03

10−6

2.35

10−6

3.63

10−5

2.46

10−5

0.03

20.03

2

2015

1.2

162.4

1,50

52.94

10−6

2.35

10−6

3.63

10−5

2.46

10−5

0.03

60.03

1

3510

1.2

251.2

1,04

13.80

10−6

1.93

10−6

3.73

10−5

1.80

10−5

0.04

50.03

1

3510

1.2

252.4

2,08

13.80

10−6

2.43

10−6

3.73

10−5

1.93

10−5

0.04

80.03

9

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DEtOHk ¼ K0

8Rg

pMEtOH

� �0:5

ð12Þ

whereK0 ¼ "dp=3tis a function ofmembrane porosity (ε), porediameter of membrane (dp) and membrane tortuosity (τ).

The flux of ethanol across the membrane is then calcu-lated by the following equation:

J ¼ KovPsatðaf � asÞ ð13Þ

in which it was assumed that temperature of feed and strippingstreams is the same and Psat is the saturation pressure ofethanol at that temperature. af and as are the ethanol activityin feed and stripping stream, respectively, that can beexpressed as function of activity coefficient (γ) and the molarfraction (x) of ethanol. The activity coefficients were calculat-ed by the group contribution method Universal FunctionalActivity Coefficient (Witting et al. 2003). The values of masstransfer coefficients (kf, ks, Km and Kov) and of ethanol flux (J)calculated by the previous equations in different conditions (asthose used in the experiments) are reported in Table 3.

Results and Discussion

Dealcoholization of Hydroalcoholic Solutions

The influence of process parameters such as: flow rate ofstripping and feed streams, number of cycles, initial ethanolconcentration and temperature, on the effectiveness of alcoholremoval by membrane was investigated and results discussedin the following paragraphs.

From experimental data, the ethanol flux (Jexp) was cal-culated and reported in Table 3 (last column) at differentexperimental conditions, close to the corresponding values

calculated by theory (Eq. 5–13). From the comparison, theexperimental and theoretical values of ethanol flux seem ingood agreement. Moreover, with respect to mass transfercoefficients, Kov results mainly affected by the Km.

Effect of Feed and Stripping Rate

First dealcoholization tests were carried out on a modelhydroalcoholic solution at 10 %vol, keeping the temperatureof both feed and stripping streams at 20 °C. The effect of thestripping stream flow rate on the dealcoholization rate wasevaluated changing Qs in the range of 1.2–5.6 mL/min,while in the shell side the feed stream flowed at 1.2 mL/min. Evolution of alcohol content during the dealcoholiza-tion process was reported in Fig. 2.

Fig. 2 Ethanol content (percent volume) in retentate during dealcoho-lization at Qf01.2 mL/min varying the stripping flow rate: Qs01.2–5.6 mL/min; Cf010 %vol; T020 °C

Fig. 3 Ethanol content (percent volume) in retentate during dealcoho-lization at Qf02.4 mL/min varying the stripping flow rate: Qs02.4–8.6 mL/min, Cf010 %vol, T020 °C

Fig. 4 Ethanol content (percent volume) in retentate during dealcoho-lization at different feed flow rate: Qf00.6–5.6 mL/min, Qs02.4 mL/min, Cf010 %vol, T020 °C

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Increasing the stripping flow rate from 1.2 to 2.4 mL/min, ahigher decrease in ethanol content was observed. After fivecycles, in fact, the ethanol content in the retentate was 2.4 %vol at 2.4 mL/min and 3.5 %vol at 1.2 mL/min. Since theinitial volume of hydroalcoholic solution was 200 mL, the fivecycles lasted about 835 min. For Qs values higher than2.4 mL/min (3.6 and 5.6 mL/min), a higher alcoholic contentin the retentate (4.8 and 5.2 %vol, respectively) was found atthe end of the fifth cycle.

These results in terms of ethanol flux are in agreementwith the values calculated by theory (Table 3), especiallywhen stripping stream (Qs01.2–2.4 mL/min) is in laminarconditions (Re<2,000). In particular, it was found that eth-anol flux and corresponding Kov values in transient or tur-bulent conditions (Qs03.6–5.6 mL/min) are lower than

those in laminar flow (Qs01.2–2.4 mL/min), but in bothflow regimes, Kov increases increasing the stripping flowrate. Hence, when the stripping agent flowed under transi-tion or turbulent regime (Re>2,000), a lower dealcoholiza-tion efficiency of the membrane was found.

Further tests were performed at a fixed value ofQf (2.4 mL/min) and increasing Qs in the range 2.4–8.6 mL/min (Fig. 3).After five cycles (415 min), the results showed lower alcoholcontent (about 6.4 %vol) in retentate at 2.4 and 8.6 mL/minthan 5.6 mL/min, where the alcohol content was 7.2 %vol.

Also in this case, the experimental ethanol flux resultsmatched the values of those calculated by the theory(Table 3): the overall ethanol mass transfer coefficients Kov

in turbulent conditions increase increasing the stripping flowrate (from 5.6 to 8.6 mL/min), reaching values close to thosefound in laminar conditions (2.4 mL/min).

In order to evaluate the influence of the feed flow rate onethanol transfer, tests were carried out changing Qf in therange from 0.6 to 5.6 mL/min at Qs equal to 2.4 mL/min.From Fig. 4, it appears that increasing the feed flow rate upto 1.2 mL/min the dealcoholization rate increases, but fur-ther increase in Qf (3.6–5.6 mL/min) does not have anysignificant effect. In detail at Qf values of 1.2 mL/min, aremarkable alcohol decrease in retentate (up to concentra-tion of 2 %vol) was observed in about 15 h of process. Alsoin these test conditions, small differences between the mea-sured and calculated ethanol flux values were found. Theo-retical ethanol flux and mass transfer coefficients increasenot linearly increasing the feed flow rate: at 1.2 mL/min, theKov is 1.05 times higher than that at the lowest flow rate(0.6 mL/min), while at higher Qf (3.6 and 5.6 mL/min,respectively) the increase of Kov with respect to 0.6 mL/min was lower (about 1.10 times). The data of Jexp reported

Fig. 6 Comparison of ethanolloss (percentage) duringdealcoholization at differenttemperatures: 15, 20, 35 °C;Qf01.2 mL/min; Qs01.2 mL/min; Cf010 %vol

Fig. 5 Ethanol loss (percentage) vs. dealcoholization cycles at differ-ent initial ethanol contents: Cf010, 12.5, 15 %vol, Qf01.2 mL/min,Qs02.4 mL/min, T020 °C

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in Table 3 highlight a higher effect of the increase in feedflow rate on the ethanol flux up to values of 1.2 mL/min.

Effect of Initial Ethanol Concentration

Three hydroalcoholic solutions at different concentrations(10, 12.5, 15 %vol) were investigated. Test conditions (i.e.flow rates of feed and stripping equal to 1.2 and 2.4 mL/min,respectively) were chosen on the basis of the previousresults. The results were shown in Fig. 5 where the loss ofethanol (percentage) in retentate was reported vs dealcoho-lisation cycle. It has to highlight that the highest ethanolremoval (76 %) was obtained starting from a hydroalcoholicsolution of 10 %vol after five cycles of dealcoholization(about 670 min), while ethanol removal of 49 and 46 %,respectively, for 12.5 and 15 %vol hydroalcoholic solutions,were found. It was expected that the increase in vapourpressure difference across the membrane with an in-crease in the concentration of ethanol in the feed solu-tion, resulted in an increased driving force for ethanoltransport through the membrane, as also predicted bytheory. Probably, the increase of ethanol concentration in thefeed streamdetermines a rapid saturation of themembrane poresby ethanol, already in the first dealcoholization cycle, and con-sequently a reduced exchange of ethanol between the twostreams.

Effect of Process Temperature

Finally, the effect of temperature on dealcoholization efficien-cy was investigated performing tests at temperatures in therange 15–35 °C. The tests were carried out on model hydro-alcoholic solution (10 %vol) at a feed flow rate of 1.2 mL/min

for two stripping flow rate values: 1.2 and 2.4 mL/min.Results of ethanol loss in retentate as function of number ofdealcoholization cycles at different temperatures werereported for Qs 1.2 and 2.4 mL/min in Figs. 6 and 7, respec-tively. At a given stripping flow rate, increasing the tempera-ture the ethanol flux increases because of the higher vapourpressure of ethanol at higher temperatures (according toAntoine’s equation). Moreover, an increase in mass transfer

Table 4 Chemical and physical parameters of Aglianico and deal-coholized wine

Analysis Aglianico wine Dealcoholizedwine

Alcohol content (% vol) 12.55±0.1a 10.65±0.24b

Total acidity (tartaric acid g/L) 5.61±0.03a 5.86±0.15a

Volatile acidity (acetic acid g/L) 0.44±0.01a 0.43±0.02a

Colour intensity 1.04±0.03a 1.02±0.09a

Tonality 0.89±0.02a 0.88±0.03a

OD 420 nm (%) 40.15±0.6a 40.25±0.8a

OD 520 nm (%) 44.94±0.8a 45.54±0.7a

OD 620 nm (%) 14.91±0.3a 14.21±0.9a

Polyphenols (GAE mg/L) 2,447.0±147.40a 2,440.1±231.74a

Lactic acid (mg/L) 2,546.0±101.55a 2,489.3±96.13a

Acetic acid (mg/L) 972.8±11.74a 1,030.5±56.72a

Succinic acid (mg/L) 150.9±16.90a 157.1±9.63a

Malic acid (mg/L) 670.5±44.31a 746.8±35.53a

Tartaric acid (mg/L) 1,550.4±15.67a 1,629.7±45.83a

Ascorbic acid (mg/L) 12.2±2.46a 16.0±1.96a

Ossalic acid (mg/L) 320.6±0.49a 343.5±15.03a

Citric acid (mg/L) 526.3±13.03a 552.4±26.80a

GAE gallic acid equivalents

Fig. 7 Comparison of ethanolloss (percent) duringdealcoholization at differenttemperatures 15, 20, 35 °C; Qf01.2 mL/min; Qs02.4 mL/min;Cf010 %vol

Food Bioprocess Technol

coefficients (ks, kf, and Km) by temperature was due to theincrease in density and ethanol diffusivity, and the decrease inviscositywhich determines an increase in bothRe andSc numb-ers. Anyway, the effect of temperature on ethanol flux predictedby theory is sensibly higher than that found from experiments.

Wine Dealcoholization

Dealcoholization of Aglianico wine, up to a maximum of2 %vol, was carried out (Commission Regulation (EC) No.606/2009). The results of tests (Table 4) performed at 20 °Cshowed an alcohol decrease of 1.9 %vol corresponding to apercentage decrease of 15 % with respect to the initialcontent of alcohol in wine, as expected by preliminary tests.Among the chemical and physical parameters investigated(Table 4), no significant differences (p<0.05) were observedbetween Aglianico wine and dealcoholized wine. Great in-terest assume the total polyphenols content that, in additionto contributing to the colour of the wine, is very importantfor the potential beneficial effects on human health (Fan-zone et al. 2012). No significant differences (p<0.05) werefound between Aglianico and dealcoholized wine. Compar-ison of the total polyphenols content measured in this studywith literature values (Di Majo et al. 2008) showed that ourdata is in agreement with values detected for other Italianred wines, although large differences in the total polyphe-nols content depend on grape varieties, winemaking tech-nique and geographical locations (Šeruga et al. 2011). It isof interest to know how the different grape varieties canhave different acid contents, and therefore cause differencesin acid taste. The Aglianico wine, used for the dealcoholiza-tion tests, showed a quali-quantitative profile of the organicacids in accordance with a red wine composition, wheretartaric, lactic, malic and citric acids are the most abundantacids (Clarke and Bakker 2004). No significant differences(p<0.05) between Aglianico and dealcoholized wine weredetected for organic acids, total and volatile acidity (Table 4).In order to highlight possible changes to the colour propertythat assumes a great importance for the visual evaluation ofquality of a red wine, parameters such as CI, To, OD at 420,520, 620 nm of wine and dealcoholized samples wereinvestigated.

Aglianico wine was characterized largely by red (OD420 nm) and yellow (OD 520 nm) pigments that contributefor 45 and 40 %, respectively, to the colour of wine. Theblue pigments (OD 620 nm) participate to the wine colour inlow measure but are essential in giving the typical red–bluish colour of Aglianico wine. After the dealcoholizationprocess, the percentage of yellow, red and blue pigments didnot show significant differences with respect to the initialvalues. Colour intensity and tonality values of Aglianico anddealcoholized wine fell within the range reported byRibéreau-Gayon et al. (2006), for different red wines, without

significant differences between the two samples. The compar-ison between chemical and physical parameters of Aglianicobefore and after the dealcoholization process highlighted thatthe removal of ethanol content by osmotic distillation does notmodify the main parameters that affect the quality of red wine.The effect of dealcoholization on aroma compounds should bedetected. This latter is under study.

Conclusions

Osmotic distillation is a novel membrane process utilised forthe partial removal of ethanol from wine. The effect ofvarious process parameters, such as flow rate of feed andstripping agent, initial ethanol concentration in feed streamand temperature on the effectiveness of dealcoholizationprocess showed that:

& the optimal conditions for ethanol removal from modelsolutions at 10 %vol were obtained working in laminarconditions for both feed and stripping streams;

& the increase in the concentration of ethanol in feedsolution resulted in a decrease of ethanol flux throughthe membrane, probably due to saturation phenomena;while an increase in temperature accelerates the deal-coholization process.

The feed and stripping agent mass transfer coefficientswere estimated based on classical empirical correlation ofdimensionless numbers (Re, Sc, Sh), whereas membranetransfer coefficient was estimated using the dusty gas model.The major contribution to the transport resistance was due tothe membrane in agreement with literature results. Theoverall mass transfer coefficient and the ethanol flux calcu-lated from the proposed correlations were found to describequite well most of the experimental data for the conditionsinvestigated. The comparison between the main propertiesof Aglianico wine before and after the dealcoholizationprocess highlighted that osmotic distillation does not modifythe wine quality.

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