Stabilization table wine

Enological techniques have developed over the past 10-20 years so that it is possible now for the commercial-scale winery to ensure the biological stability in the bottle of young sweet table wines. This has made possible the production and marketing of inexpensive sweet white table wines and the introduction of balanced, pleasant-tasting, low-sugar reds as well. It has led further to the introduction of the very sweet Concord or berry-flavored red table wines and to the development of a host of sweet wines of various colors specially flavored with mixtures of extracts of fruits, berries, and herbs. 

In addition to alcoholic fermentation, a malolactic fermentation by certain desirable strains of lactic acid bacteria needs to be considered. Occasionally, wild strains produce off-flavors. Malolactic fermentation is desirable in many red table wines for increased stability, more complex flavor, and sometimes for decreased acidity. Selected strains are often added toward the end of alcoholic fermentation. All the malic acid present is converted into lactic acid, with the resultant decrease of acidity and liberation of carbon dioxide. Obviously this has more effect on the acidity the more malic acid is present, and this is the case in wine from underripe, too-tart grapes. Once malolactic fermentation has occurred, it does not recur unless another susceptible wine is blended. 

While the above description adequately describes the bottling of V. vinifera table wines, the majority of the fruit and berry wines are bottled without membrane filtration. Virtually all of these fruit and berry wines have potassium sorbate added to them to ensure microbial stability. 

Potassium sorbate is used as a yeast inhibitor for the stabilization of table wines containing residual sugar. When conditions permit the growth of lactic acid bacteria, wines treated with sorbic acid can develop an odor resembling crushed geranium leaves (Burkhardt, 1973 Radler, 1976 Wurdig et al., 1975). This result due to bacterial reduction... 

Table 1.16. Influence of pre-treatment on the physicochemical parameters of a cold-stabilized white wine. Wines treated with slow cold-stabilization (10 days at —4°C). Assessment of protective effects (Maujean et al., 1985)...

Potassium bitartrate and calcium tartrate are responsible for the physical stability of wines. A portion of tartaric acid slowly esterifies with ethanol to form ethyl bitartrate. Malic acid is converted to lactic acid (0-2.5 g/L) during malolactic fermentation, and the taste of wine becomes weaker. Succinic and acetic acids are also formed during fermentation [18,19]. The content of organic acids in vinegar and wines is shown in Table 10.7. 

The use of sodium or potassium benzoate is approved by BATF for stabilization of wine coolers but not table wines. Although permitted for use at levels up to 1000 mg/L, sensory considerations require use at much lower levels. In wine coolers, benzoate is frequently used in combination with sorbate and SO2. The combination provides the needed level of antimicrobial activity at concentration levels that are generally not sensorially objectionable (Zoecklein et al., 1995). Carbonation may also enhance antimicrobial effects. In soft drinks, Schmidt (1987) reported linear decreases in the concentration of sodium benzoate required with increases in carbonation. 

Unfortunately, in spite of the published literature on wine proteins, we do not know the actual protein levels at which table or dessert wines are stable. The changes in protein content during production and processing of wines are still not known with sufficient accuracy to predict their behavior. The winemaker has to depend on empirical tests if he is to produce protein stable wines. Early separation of new wines from their fermentation yeast greatly improves their chances for protein stability by decreasing the release of yeast autolysis products into the wine. 

Traditional practices, such as white wine aging on lees in barrels for several months, confer the wine s tartaric salt stability, which dispenses them from any cold stabilization treatment. It has indeed been observed (Moine-Ledoux and Dubour-dieu 2007) that, in the Bordeaux wine-growing area, the majority of dry white wines aged on lees which are not stable in March after their first winter but become stable in June or July without any supplementary cold treatment (Table 5.1). In contrast, wines within the same crus which are not aged on lees systematically undergo cold treatment to obtain stability regarding tartaric salt crystallization. 

Table 5.1 Evolution of tartaric salt stability estimated by cold testing (six days at —4°C) of different white wines aged on lees throughout two vintages (Reprinted with authorization from Moine-Ledoux and Dubourdieu 2007)...

Table 5.2 Tartrate stabilization of various white wines by adding Mannostab as determined by visual observations of potassium bitartrate crystallization within six days at —4°C (redrawn with permission from Moine-Ledoux et al. 1997)...

Enzyme-extracted mannoproteins from the yeast cell wall added at a dose of 25 g/hL, can reduce by half the bentonite dosage necessary for protein stabilization of a very hazy wine (Table 5.3). During lees autolysis, MP32 is released from the... 

Table 1.10. Composition of Chardonnay wines after tartaric stabilization, depending on the time of acidification (addition to must or wine after malolactic fermentation). Cuvees were acidified with 1 g/1 tartaric acid and second pressings with 1.5 g/1. (Dartiguenave, 1998)...

The unreliability of this result is confirmed by the experiment described in Table 1.14, involving a wine with an initial PCk of 9.17 x 10, maintained at 30°C, in which increasing concentrations of commercial cream of tartar were dissolved. It was observed that, when the PCk of a wine was doubled (e.g. wine +0.2 g/1 of dissolved KTH and wine +1 g/1 of dissolved KTH) the percentage drop in conductivity was the same, although there was obviously a difference in stability. 

Table 1.14. Demonstrating the limitations of the reliability of the mini-contact test in assessing the stability of a wine by adding increasing quantities of potassium bitartrate and measuring the percentage drop in conductivity...

The spontaneous crystallization temperature of each sample of treated wine (Table 1.16) was also determined using the same procedure. Examination of the results shows that a wine filtered on a 10 Da Millipore membrane, i.e. a wine from which all the colloids have been removed, has the lowest value for the supersaturation field (Tsat - Tcso), closest to that of the model dilute alcohol solution. Therefore, the difference between the results for this sample and the higher values of the supersaturation fields of fined samples define the effect of the protective colloids. It is interesting to note that the sample treated with metatartaric acid had the widest supersaturation field, and cold stabilization was completely ineffective in this case. This clearly demonstrates the inhibiting effect this polymer has on crystallization and, therefore, its stabilizing effect on wine (Section 1.7.6). Stabilization by this method, however, is not permanent. 

Table 1.17. Changes in the physicochemical parameters of cold-stabilized wine when the contact tartrate was recycled (Manjean et al., 1986)...

With this in mind, its effectiveness has been compared to that of two other tartrate stabilization methods continuous contact cold stabilization and the addition of metatartaric acid (Table 1.21). This comparison was carried ont by measuring spontaneous crystallization after the addition of KHT (Section 1.6.4). The values obtained indicate the effectiveness of protective colloids, even if they do not necessarily correspond to the instability temperatnres. The addition of 15 g/hl of Mannostab to wine 2 and 25 g/hl... 

Table 5.6. Turbidity levels (NTU) after different protein stability tests carried ont on a Sauvignon Blanc wine during barrel aging on the lees (V. Moine-Ledoux, 1997, unpublished results)...

Table 10.1. The main treatments available for clarifying and stabilizing wines. They are not all recognized by legislation in every country and several are not permitted in the European Union...

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