Clarification and Stabilization

Suitable measures should not only eliminate any turbidity present, but also prevent its formation during storage (fining). 

Turbidity-causing solids are mostly proteins as well as oxidized and condensed polyphenols. Furthermore, multivalent metal ions can cause discoloration and sediments. Wine clarification is usually achieved by precipitation reactions, filtration or centrifugation. In blue-fining the excess metal ions which are responsible for metal-induced cloudiness (iron, copper and zinc) are precipitated by precisely calculated amounts of potassium ferrocyanide. In this process, soluble Berlin blue is formed first, 

The clarification by filtering involves pads of asbestos, cellulose, infusorial earth, and filter aids such as Hyflo Super Cel and Filter Cel. The fil- 

Suitable measures to prevent crystalline sediments in the bottle are, e. g., cooling the wine for a few days to 0 °C, addition of metatartaric acid (cf. 20.2.4), and reducing the concentrations of potassium, calcium, and tartaric acid by electrodialysis. Excessive concentrations of calcium produced by deacidification measures (cf. 20.2.5.4) can also result in additional crystal sedimentation (calcium tartrate, calcium mucate, and calcium oxalate). The elimination of excess calcium with D-tartaric acid is recommended as a counter-measure. 

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Fig. 1. An amplified outline scheme of the making of various wiaes, alternative products, by-products, and associated wastes (23). Ovals = raw materials, sources rectangles = wines hexagon = alternative products (decreasing wine yield) diamond = wastes. To avoid some complexities, eg, all the wine vinegar and all carbonic maceration are indicated as red. This is usual, but not necessarily tme. Similarly, malolactic fermentation is desired in some white wines. FW = finished wine and always involves clarification and stabilization, as in 8, 11, 12, 13, 14, 15, 33, 34, followed by 39, 41, 42. It may or may not include maturation (38) or botde age (40), as indicated for usual styles. Stillage and lees may be treated to recover potassium bitartrate as a by-product. Pomace may also yield red pigment, seed oil, seed tannin, and wine spidts as by-products. Sweet wines are the result of either arresting fermentation at an incomplete stage (by fortification, refrigeration, or other means of yeast inactivation) or addition of juice or concentrate.

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. 

Clarification and Stabilization Combinations. Wine clarification may be combined with a stabilization step to minimize handling of the wine. This type of clarification, timing, and sequence vary from winery to winery. Some options used are, after fermentation, rack the wine off yeast lees, bentonite fine for heat stability and chill for cold stability, then diatomaceous earth filter to remove remaining yeast, bentonite, and tartrate crystals after fermentation, centrifuge the wine to remove yeast solids, then chill and add bentonite, and filter to remove yeast and add bentonite, chill, then pad filter to remove bitartrates and protein. 

Many of the wine macro-components (e.g. carbohydrates, proteins, polyphenols), come from the skins and the pulp of grapes and from the cell walls of the yeast. Although this varies, the molecular weight of the majority of macromolecules is over 10,000 D and their final concentration ranges from 0.3 to 1 g/L (Voilley et al. 1991). Most macromolecules will be eliminated by clarification and stabilization treatments of the wine. Because of their interactions with wine aroma... 

The role of carbohydrate colloids in wine clarification and stability has been studied much more extensively. Pectic substances in wine foul filter layers (Castino and Delfini, 1984) during filtration. This phenomenon is particularly marked in tangential microfiltration (Section 11.5.2) (Feuillat and Bernard 1987 Serrano et al., 1988) as the carbohydrate colloid retention rate may be over 50%. A much higher proportion of AGPs than yeast mannoproteins is retained in this process (Brillouet et al., 1989 Belleville et al., 1990). 

Table 10.1 summarizes the treatments that promote clarification and stabilization, although... 

VDN are subject to the same clarification and stabilization problems as other wines. Iron casse, proteic casse, tartrate deposits and colored matter can cloud the wines. Standard preventive measmes can help to avoid these problems. Oxidasic casse is another accident linked to grape rot. 

Removing water from lettuce after washing it in a salad spiimer Separating particles from an air-flow using cyclonic separation. The clarification and stabilization of wine... 

As with filtration, there is the risk of some loss of flavor with fining due to desirable flavor molecules being precipitated out along with the more undesirable particles. Some producers of premium wine will do less fining or do it much later in the production process in order to leach as much flavor and aromatics from the phenols before they are removed. Still, fining is considered a less harsh process than filtration, with its advocates believing that it better mimics the natural clarification and stabilization process. 

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