Alcoholic fermentation clarification

After completion of the alcoholic fermentation in tanks or barrels, wine becomes a colloidal solution as well as a colloidal suspension. The particle density, which is close to that of the wine, electric repulsion forces and diffusion phenomena lead to very slow and insufficient spontaneous clarification. Moreover, natural... 

The main volatiles in wines are the higher aliphatic alcohols, ethyl esters, and acetates formed from yeasts during fermentation. Acetates are very important flavors characterized by fruity notes, C4-Ci0 fatty acid ethyl esters manly confer fruity scents to the wine. Other wine aroma compounds are C6 alcohols, such as 1-hexanol and cis- and trans-3-hexen-l-ol, 2-phenylethanol, and 2-phenylethyl acetate. Contents of these compounds in wine are linked to the winemaking processes used fermentation temperature, yeast strain type, nitrogen level in must available for yeasts during fermentation, clarification of wine (Rapp and Versini, 1991). Much literature on the wine aroma compounds was reported in reviews by Schreier (1979) and Rapp (1988). 

Because the presence of yeasts can represent a logistical bottleneck in postfermentation clarification, an alternative that has been studied is the use of immobilized microorganisms. Here, yeasts are trapped in calcium alginate beads or strands that are collectively packed into a synthetic mesh sleeve that is immersed into the juice/must. Relatively few yeasts (<10V mL) escape the encapsulation matrix (Yokotsuka et al., 1993) but yet conduct an active alcoholic fermentation. Yajima and Yokotsuka (2001) reported that concentrations of some undesirable volatile compounds (methanol, ethyl acetate, and acetaldehyde) were lower in wines made using Saccharomyces immobilized in double-layer beads. Immobilized yeasts... 

In white winemaking, this deacidification should be effected after must clarification but before fermentation. Aromatic ester production by yeasts is facilitated by a moderate pH. Conversely, this treatment permits a more precise deacidification of red wines when performed at the end of alcoholic fermentation, at the time of running off. It can also help to trigger malolactic fermentation. 

Muller-Spath (1977) was the first to contest the need to sulfite white juice before alcoholic fermentation. His research clearly showed that adding pure oxygen to non-sulfited juice before clarification improves the stability of white wine color without producing oxidation-type flaws. This process, called hyperoxidation or hyperoxygenation, consists of oxidizing juice polyphenols to precipitate them during clarification and eliminate them during alcoholic fermentation. 

Fig. 13.11. Influence of must turbidity on yeast populations during alcoholic fermentation CS, cold settled must CC, coarse clarification CN - - SM, centrifuged must + soluble macromolecules CE, cold settling + enzymatic clarification CN centrifuged must CN + HF, centrifuged must - - colloidal haze...

The production of heers and ciders requires the fermentation of sugary fluids hy the action of yeasts, and the cooling, filtration, clarification and storage of the resulting alcohol-water mixture. 

At the end of alcoholic and malolactic fermentation, the wine undergoes clarification and stabilization prior to bottling the phase inappropriately called "aging." This is the final step in winemaking, which involved those operations required to permit the expression of features considered necessary to the wine s overall quality. Nuances that distinguish wine styles also develop. 

Inorganic membranes have also been used in the clarification of other fermented alcoholic beverages such as beer and vinegar in recent years. Two important applications of membrane filtration for beer production are the removal of bacterias and beer recovery from the so-called tank bottoms. They are treated in the following. 

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