Wines, aerated

In practice, these various conditions must be taken into account in aging red wines, and modulated according to the type of wine. Aeration is desirable at the beginning, to degas the wine and promote the stable, purplish-colored combinations with ethanal that develop from only slightly polymerized tannins. Aeration should then be reduced to maintain a high oxidation-reduction potential, as this is favorable to the evolution of tannins. Aeration should... 

Fig. 9.4. Evolution of oxidation-reduction potential of reduced wines, aerated after the addition of 100 mg of ascorbic acid per liter, compared with control wine (Rib6reau-Gayon et ah, 1977). (A) Red wine control. (B) Red wine + ascorbic acid. C) White wine control. (D) White wine + ascorbic acid...

Non-stirred, aerated vessels are used in the process for traditional products such as wine, beer and cheese production. Most of the newly found bioprocesses require microbial growth in an aerated and agitated system. The percentage distribution of aerated and stirred vessels for bioreactor applications is shown in Table 6.1. The performances of various bioreactor systems are compared in Table 6.2. Since these processes are kinetically controlled, transport phenomena are of minor importance. 

Non-stirred, non-aerated vessels are used for traditional products such as wine, beer and cheese. Most of the new products require growth of microorganisms in aerated, agitated vessels. 

There is also an expectation that thiols can be directly oxidized through to disulfides (RSSR in Fig. 4.4B) (Mestres et ah, 2000 Rauhut et ah, 1996), a mechanism also suggested for the case of 3MH (Murat et ah, 2003) where a protective effect from anthocyanins present in the wine was noted. In one study, the concentrations of both ethanethiol and the related oxidized form of diethyl disulfide in a red wine were found to decrease over a 60-day period, and at a greater rate under aeration (Majcenovic et ah, 2002). However, in a survey of wines over five vintages, the older wines were shovm to contain higher concentrations of diethyl disulfide, and lower concentrations of ethanethiol (Fedrizzi et ah, 2007). 

As the new wine nears the completion of its primary alcoholic fermentation, it should be analyzed carefully for both alcohol and sugar. If fermentation slows too much, the wine may be gently aerated by racking (siphoning, pouring, or pumping) it from one container to another, and, if the temperature has dropped to 60 °F or below, it should be warmed to about 70 °F and held until all the sugar has been converted to alcohol. 

In the past decade, some North Coast wineries have experimented with a completely anaerobic fermentation technique known as carbonic maceration. In this system, whole grapes are placed in a vat and fermentation is allowed to start. Since there is no pumping over or aeration, the fermentation proceeds very slowly under a blanket of carbon dioxide. The fermentation relies upon the intercellular production of ethanol to kill the skin cells and release the color and tannins. The results are claimed to be wines with a special bouquet, earlier maturity, slightly more alcohol, and a softer taste. They are easily recognizable by their special bouquet. Although popular in France, where they are drunk very young, they have not gained widespread acceptance with the North Coast wineries. 

Fornachon (5) in Australia found that a yeast suspension aerated and agitated in an alcoholic solution produced aldehyde. He reported his extensive research on flor sherry production to the Australian Wine Board (6). 

Most wineries in Washington are adding the malo-lactic starter at the point where the wine is separate from the pomace. At completion of malo-lactic fermentation, the wine is racked from its lees and often aerated. This aeration is accomplished by racking into a sump or racking the wine through the top door of the receiving tank. The total S02 content is adjusted to a minimum of 60 mg/L at this time. 

Subsequent handling of red wine is not greatly different from that of white wine holding for a while at a moderate temperature (about 18.3° C) (65° F) and without S02 to complete malo-lactic fermentation promptly, with or without lactic bacterial inoculation. Several rackings follow, the first one usually with some aeration and always with addition of S02 once the malic... 

The fluidity of the plasmatic membrane is considerably affected by temperature (Rodriguez et al. 2007) and ethanol concentration (Jones and Greenfield 1987). Therefore, during alcoholic fervaeniaiionSaccharomyces cerevisiae must adapt the fluidity of the membrane to the changing environmental conditions. It should be emphasized that the temperature of fermentation and aeration depend on the type of winemaking. Usually, white wines are made at low temperatures (14-18 °C) and without aeration to conserve aromas whereas red wines are fermented at relatively high temperatures (28-30 °C) and are aerated in order to enhance colour extraction. 

Aerating wine under biological aging on a monthly basis has been found to inhibit partially ADH I and ADH II enzyme activity immediately upon aeration. However, once all oxygen has been used by the yeasts and become a limiting factor again, ADH II activity rises, possibly as a result of the need to alleviate the excess of NAD+ accumulating by effect of oxidative metabolism and maintain the redox... 

Yeast strain, and nutrient status of the must and fermentation conditions, many of which affect growth or induce physiological stress, modulate the accumulation of acetic and other fatty acids in wine. Reported factors include must sugar concentration, nutrient balance, inoculum level, fermentation temperature, pH and aeration (Delfini and Costa 1993 Henschke and Jiranek 1993 Shimazu and Watanabe 1981). The effects of osmotic stress, as induced by sugar concentration, on acetic acid production are discussed in Sect. 8D.3.2. 

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