Nanofiltration and reverse osmosis in winemaking

Nanofiltration and reverse osmosis in winemaking

Desalination 231 (2008) 283–289 Nanofiltration and reverse osmosis in winemaking A. Massota, M. Mietton-Peuchota*, C. Peuchotb, V. Milisica a Equipe...

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Desalination 231 (2008) 283–289

Nanofiltration and reverse osmosis in winemaking A. Massota, M. Mietton-Peuchota*, C. Peuchotb, V. Milisica a

Equipe Génie des Procédés et Environnement, UMR Œnologie INRA), Université Bordeaux 2, France Tel. +33 (5) 5684 6495; Fax +33 5 5684 6468, -97; email: [email protected] b Institut de la Filtration et Techniques Séparatives, Agen, France

Received 9 June 2007; accepted revised 20 October 2007

Abstract The paper is an overview of the application of membrane processes to winemaking. The aim is to present both the application of membrane processes in winemaking and a general philosophy of their development from a process engineering point of view. Several examples illustrate this approach, in particular applications of nanofiltration and reverse osmosis membranes, but the other techniques such as microfiltration, ultrafiltration and electrodialysis are also mentioned. The principal condition for further development of membrane processes in winemaking is a good understanding of membrane techniques, separation techniques and characterisation of the membrane itself and the product (must or wine) to be filtered. The last constrain, given the complexity and variability of must and wine composition, is not trivial and needs a considerable effort at both industrial and research levels. For the same reasons, the coupling of the membrane and other physico-chemical treatments appears to be a promising research domain. Keywords: Wine; Membrane filtration; Alcohol content control; Nanofiltration

1. Introduction Membrane filtration has been applied to wine for a long time. It should be noted that 0.65 μm and 0.45 μm filtration cartridges very often used in oenology, are made from membranes. In the *Corresponding author.

past, the membrane material was not adapted to the wine filtration, but at present, the clarification cartridges suit perfectly and are integrated in all bottling units. Subsequently, in a cross-flow filtration mode, microfiltration membranes were the first to be applied for wine clarification. The main advantage of membranes over cartridges was their ca-

Presented at International Workshop on Membranes and Solid–Liquid Separation Processes, INSA-Toulouse, France 11 July 2007 0011-9164/08/$– See front matter © 2008 Elsevier B.V. All rights reserved doi:10.1016/j.desal.2007.10.032

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pacity to accept a higher solid concentration in the retentate. Initially, the mineral and organic membranes were proposed with 0.2 μm cut-off and were used in the final clarification of wines. That application was first developed for the treatment of large volumes, and afterwards spread to other domains, for example, to noble-rotted sweet wines. Today, microfiltration is largely used in oenology for must, lees and wine filtration at different membrane cut-off, from 0.1 to 1.2 μm. The development of reverse osmosis application in must concentration was practically done in parallel with that of microfiltration in clarification [1,2]. However, in both cases two problems slowed their developments; one was technological and the second was legislative. The first rose from the fact that the classical RO modules were designed essentially for water treatment applications where suspended solid concentrations are low and particle sizes are small [3]. New design (double spacer for spiral modules), more efficient pre-treatment before concentration and better knowledge of the product to be filtered enabled the development of that technique. The RO membranes being very selective, let through only very small molecules or ions. For example, RO wine permeate contains water, alcohol, acetic acid (60% of the initial concentration), ethylic acetate (40% of the initial concentration) and lactic acid (15% of the initial concentration) [4,5]. The retention rates are a function of the selected membrane characteristics. The level of concentration is limited by osmotic pressure generated by the process itself and by the applied pressure. With recent advances in nanofiltration membrane processing different new applications in oenology can be foreseen. The complex separation mechanisms that occur in nanofiltration (physical, chemical and electrical interaction between the solvent, solutes and membrane) make the number of the operating parameters that control separation efficiency long and give different results for the same feed and the same membrane [6]. The specific performance of nanofiltration

membranes and the large choice of the membranes should facilitate their application and increase the possibilities for coupling with other membrane techniques (reverse osmosis–nanofiltration, ultrafiltration–nanofiltration) with the objective of performing corrections to must or wine by reducing or increasing the concentration of a given solute. So, for must it is possible to apply the combination of RO–NF instead of a sole reverse osmosis stage as it can treat a smaller quantity of must and obtain a higher sugar concentration in must (up to 45°Brix, [7]). These corrections aim to provide a better equilibrium and to improve the stability of wine. Membrane processes could also be coupled with ion exchange treatment or with vacuum evaporation. At present, that kind of application is being tested experimentally or is already practised in some countries for: • Alcohol content control by its partial removal from wines or by partial sugar removal from musts; • Volatile acidity reduction in wines; • Acidification of wines; • Flaw (defect) elimination. 2. Control of alcohol content The studies on control of alcohol content of wines by partial removal of alcohol or sugar from must are initiated by the problems of over concentration of sugar and alcohol that some countries frequently face, or by the new social trends of limiting alcohol consumption [8–10]. The production of over alcoholised wine concerns the main part of Mediterranean wine regions in France, Spain or Italy, as well as Californian and South American vineyards [11]. The problem originates from commendable wine-grower and oenological practice. It is widely known that the quality of red wines depends essentially on the maturity of phenolic components contained in grape berries. Phenolic maturity is directly linked to a high sugar concentration. Thus the grapes are

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picked having high potential alcohol content, up to 17% vol., with low acidity. This over maturity leads to difficulties in wine making: difficulties in alcoholic fermentation, in microbiological stabilisation, as well as gustatory disequilibrium (strengthening of warm sensation in wine). These problems are augmented by other administrative constraint: in some countries, as USA, a supplementary tax is added where the alcohol content is over 14.5% vol. Meanwhile, consumers show preference for wines with less alcohol content (between 9 and 13% vol.), a tendency reinforced by anti-alcohol campaigns. So, Institut de Recherche Agronomique of Pech Rouge was granted by Agence Nationale de Recherche a research project on “quality wines with reduced alcohol content”. The aim of the study is to produce wine by taking into account both aspects and other wine by-products with an alcohol content of less than 6% vol. Several French companies as IMECA, Bucher Vaslin, Michael Paetzold, InterRhône have the same objective and are developing processes that integrate systematically at least one membrane technique. This technology is already implemented in countries where the regulation permits this kind of experiments. All systems proposed at present induce to a certain extent the reduction of must or wine volumes due to the elimination of a concentrate of sugar or alcohol. This decrease in volume is related to the desired reduction in sugar or alcohol content and involves a slight concentration of other components. For example, the process of

partial sugar reduction combines an ultrafiltration membrane that allows the sugar to pass through and a nanofiltration membrane that retains the sugar. The maximum degree of concentration is limited by the resistance of the nanofiltration membrane under applied pressure (around 75 bar), noting that the osmotic pressure of the concentrate rises constantly during filtration. An example given in Table 1 shows that the maximum sugar concentration obtained is approximately 400 g/L. A second stage of treatment by evaporation could help to continue the concentration, in particular in partial alcohol removal from wine by means of two membranes with different selectivities against alcohol. Here the selectivity of the second membrane decreases strongly and so impedes the final concentration. Table 2 shows such example. The system for partial alcohol removal proposed by the Australian company Memstar involves a reverse osmosis membrane followed by a membrane contactor (Liquid Cel by Membrana). Two such plants are installed in Chile and Australia. A Californian company, Vinovation also proposes membranes for partial alcohol removal and claims that at present 10% of premium wines in USA undergo a small correction of alcohol content. 3. Volatile acidity or malic acid reduction The same company markets a system for volatile acidity reduction by coupling reverse osmo-

Table 1 Results of must concentration analyses at different stages of treatment

Raw juice CUF PUF CNF PNF

Sugar (g.L–1)

pH

Total acidity (gH2SO4.L–1)

Tartaric acid (g.L–1)

Malic acid (g.L–1)

IPT

271 311 249 428 40

3.60 3.50 3.55 3.60 3.40

2.66 4.00 2.53 3.0 1.93

3.93 5.84 3.34 4.23 2.19

0.79 0.65 0.91 0.92 0.89

19.2 118.0 3.8 6.9 0.8

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Table 2 Evolution of alcohol content (DAV) at the second stage membrane Time (min)

Permeate rate (l/h)

DAV permeate DAV concentrate (%. vol) (%. vol)

0 25 50 70 95 120 140

180 150 90 60 40 20 20

n.d 1.40 2.1 5.5 7.1 10.3 n.d

6.2 8.2 13.0 17.0 19.1 21.8 23.8

MEMBRANES 1

4

RAW WINE 3

PERMEATE TREATMENT

5

FINAL WINE

Wi

sis and ion exchange resins (weak anionic resins). This process is interesting in that it is a case where the fermentation is stopped [12,13]. The trials of volatile acidity reduction with some hundred lots enabled rapid resumption of alcoholic fermentation in 75% of lots. VA Filtration, a company from USA, proposes a technique for volatile acidity reduction based on one stage of nanofiltration followed by selective adsorption of volatile acidity (Fig. 1). The volatile acidity or malic acid reduction could also be done by coupling two stages of reverse osmosis (membrane DESAL, NaCl retention rate >99%). Since the free acids are poorly retained by the membrane, the permeate after the first stage filtration (“permeate 1”, Fig. 2) contains free acids, salts, esters and other small molecules. Once the permeate is neutralised with pH of the targeted acid, it will be retained by the second stage membrane in a salty form. The other components passing through (“permeate 2”, Fig. 2) are re-injected in the initial wine. The potassium hydroxide is used for neutralisation. During the treatment, the decrease of the acetic acid concentration in wine is progressive (Fig. 2). The rejection rate of acetic acid in first reverse osmosis varies between 40 and 50%. After the neutralisation, the rejection rate of potassium acetate in second reverse osmosis is higher than 90%.

2

Aft R

l

Fig. 1. Coupling of a membrane technique and a permeate treatment (adsorption, ion exchange resins) — general scheme.

The analyses of the wine so treated show an increase of alcohol (+0.1), of phenolic content and of colour intensity. The increase is due to a portion of neutralised permeate which corresponds to the “dead” volume of the second reverse osmosis plant not mixed with the treated wine (3% in the present case). The result is a slight rise of wine component concentration. The results presented in Table 3 show the decrease of volatile and total acidity of the treated wine and a small increase of pH (+0.02).The potassium concentration remains stable because of the equilibrium between the resulting demineralisation and the concentration of wine due to the loss of volume. The equipment for volatile acidity reduction is proposed by the Italian company VELO and that for malic acid — by the company Bucher Vaslin. The parameters that control the process and help to optimise it are an adequate choice of membrane characteristics and neutralisation conditions. 4. Others applications The elimination of wine “bad taste” appears to be a promising research subject. Chilean re-

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Volatile Acidity of wine

Permeate 2

Permeate 1

Volatile Acidity (g H 2 SO 4 /L)

0,9 0,8 0,7 0,6 0,5 0,4 0,3 0,2 0,1 0 0

200

400

600

800

1000

1200

1400

1600

Permeate volume (litres) Fig. 2. Evolution of wine volatile acidity and of permeates of two reverse osmosis stages.

Table 3 Results of physico-chimical analyses of wines before and after treatment

Alcohol content (% v/v) Total acidity (gH2SO4/l) Volatile acidity (gH2SO4/l) pH Potassium (mg/l) Total phenol index (TPI) Colour intensity

Red wine sample

Red wine treated

White wine sample White wine treated

11.5 3.92 0.71 3.56 1500 24.1 0.43

11.5 3.72 0.37 3.58 1500 27.3 0.49

9.20 7.84 0.86 3.75 1386 / /

searchers [14] explored the methods for 4ethylphenol and 4-ethylguaiacol reduction in red wines by combining nanofiltration and adsorption. The permeate obtained by nanofiltration is treated by hydrophobic adsorbent resins (XAD16HP) and recycled up to the level of desired concentration. They claim that the same process could also be used for herby taste elimination. The results show that the resin selectivity is not suffi-

9.30 7.35 0.63 3.77 1320 / /

cient. In principal, it should be possible to isolate the “bad taste” by using nanofiltration membranes, but for this elimination it would be necessary to improve the post-treatment (e.g. by adsorption, fining, etc.). The tartaric acid stabilisation of wines is usually done by cold treatment. It is progressively replaced by electrodialysis. A Californian study [15] suggests the use of nanofiltration and

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Table 4 Synthesis of proposed membrane processes Objective

Processes

Concentration of must Reduction of the sugar content in must

Reverse osmosis Ultrafiltration + nanofiltration Ultrafiltration + evaporation Reverse osmosis 1 + reverse osmosis 2 Reverse osmosis + distillation Reverse osmosis + membrane contactor Reverse osmosis + anionic resins Reverse osmosis + reverse osmosis Reverse osmosis + adsorption Electrodialysis Nanofiltration + microfiltration Nanofiltration + resins adsorption Nanofiltration + PVPP Nanofiltration+ nanofiltration Electrodialysis

Partial alcohol removal Reduction of volatile acidity Tartaric stabilisation Bad taste reduction Reduction of malic acid pH control

microfiltration for tartaric acid stabilisation. At first, the wine is concentrated by a nano-membrane until the precipitation of the tartar. The crystals are then eliminated by microfiltration and the two permeates are gathered. The process clarifies the wine at the same time. The electrodialysis experiments have been carried out by the company Eurodia with the objective of acidifing the wine by potassium retention (Table 4). 5. Conclusion The possibility of coupling several membrane techniques enables numerous new applications. It cannot be realised without a good knowledge of the membranes themselves, the transfer phenomena and the separation mechanisms. The reduction of sugar content in the must is a good example: that process represents an innovative solution, applying a well known technology. The treatment has the following advantages: • The risk of stuck fermentation is limited and it helps the winemaker have better control of extraction phenomena during vatting.

• The volume loss induced by the process provokes an enrichment of wine in phenolic components and macromolecules. • Finally, compared to alcohol, the management of sugar concentrate, from a regulatory point of view, is less problematic. The destination and denomination of the concentrate at present are discussed: “concentrated must for enrichment in sugar” or “concentrated and rectified must”. As far as alcohol is concerned, the legislation problems are certainly those that limit the development of a double stage membrane alcohol removal. The handling and destination of alcohol is an administrative problem. The membranes enabling 80% ethanol retention do exist, but the maximum concentration extent is limited to 25% vol., beyond which the retention rate decreases rapidly. Numerous other applications could be intended with the aim of bringing some corrections to must or wine, as, for example, reduction of malic acid content in must, pH control, or bad taste elimination. In all these cases, must or wine are fractioned by the membranes selected and tasted with care.

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So, the solutes to be retained are separated and the initial wine is reconstructed free of rogue components that veil its optimum quality. Acknowledgements The authors thank all companies for the data that have been used in preparation of the present article. References [1] E. Ronald, R. Nina., W. Robert, A. Keith and G Edward, J. Food Sci., 58(3) (1993) 633–637. [2] C. Delfini and G. Nicolini, J. Int. Sci. Vigne Vin, 25(1) (1991) 1–35. [3] P. Cuenat, D. Kobel and E. Zufferey, Bull. OIV, 701– 702 (1989) 519–537. [4] P. Noilet, Diplôme universitaire d’expérimentation et de Recherche en Enologie et Ampélologie. Université Victor Segalen Bordeaux 2, 2004, 135 p.

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[5] M. Mietton-Peuchot, V. Milisic and P. Noilet, Desalination, 148 (2002) 125–129. [6] V. Milisic and M. Hamachi, Proc. 3rd Nanofiltration and Applications Workshop, 2001, pp. 26–28. [7] I. Kiss, G. Vatay and E. Bekassy-Molnar, Desalination, 162 (2004) 295–300. [8] J. Regan, Fermentation, 3(4) (1990) 235–237. [9] K. Bui, R. Dick, G. Moulin and P. Galzy, Am. J. Enol. Vitic., 37(4) (1986) 297–300. [10] N. Chinaud and P. Broussous, J. Int. Sci. Vigne Vin, 25(4) (1993) 245–250. [11] J.L. Escudier, Rev. fr. œno., 119 (1989) 56–61. [12] J.E. Rasmussen, E. Schultz, R.E. Snyder, R.S. Jones and C.R. Smith, Am. J. Enol. Vitic., 46(2) (1995) 278–280. [13] C. Smith, OIV 1997, Groupe d’Expert Technologie du Vin, Office International de la Vigne et du Vin, Paris. [14] P. Ugarte, E. Agosin, E. Bordeu and J.I. Villalobos, Am. J. Enol. Vitic., 56(1) (2005) 30–36. [15] California Energy Commission, Internal Report, November 2001, 24 p.