Temperature of fermentation

The optimum temperature of fermentation of wine depends on the type, red wines working best at about 29°C while the white wines require a cooler condition of around 16°C. Heat is given off by the chemical process of fermentation. They are then traditionally matured and stored in caves or cellars at about 10°C. Much of the manufacture... 

The manipulation of the cap, the length of time the juice is kept in contact with the skins, and the temperature of fermentation are three important variables available to the enologist to produce a wine of the depth of color and flavor, degree of astringency and bitterness, and general texture and longevity that he wishes his wine to have. Later in the process there are additional variables but none is more important than these three. 

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. 

Zimmerli and Dick (1996) pointed out that apart from climatic differences, different practices in grape cultivation (e.g., use of pesticides or different cultivars, and wine making) may influence the ochratoxin A concentration in wine. The latter include time and condition of storage of harvested grapes, type of maceration, and time and temperature of fermentation. 

Fig. 19.12 The rates of fall in wort specific gravity for two temperatures of fermentation [74].

Fusel oil formation varies with yeast strain, temperature of fermentation, pH, nutritional status, suspended solids level, and oxygen concentration of juice/must. Under oxidative conditions as would occur before the onset of alcoholic fermentation, or in cases of stuck fermentation, Pichia, Hansenula, and Candida may produce substantial quantities of fusel alcohols from fermentable sugars. The fusel alcohol, 2-phenylethanol (arising from 2-phenylalanine), has the unmistakable odor of roses and is also... 

Formation. The experiments of Mestre and Campllonch (1942) support the view that acetaldehyde is an intermediary in the process of alcoholic fermentation. In some cases they report high volatile acidity arising from oxidation of aldehydes, even in the absence of bacteria. Uchimoto (1951) found a positive correlation between temperature of fermentation and amount of acetaldehyde formed. Many investigators have demonstrated a rapid rise in the aldehyde content of wines under a film yeast. Ter-Karapetian (1952) has studied the formation of acetaldehyde in 16 % alcohol wines. Aldehyde formation occurred only when the wine was aerated and yeast cells were present. Fornachon (1963) has... 

Student using a digUal thermometer to measure the temperature of fermentation in a beaker. (Martyn F. ChiUmaid/ Photo Researchers, Inc.)... 

As expected, fermentation rates by Saccharomyces 3xy viiih temperature. Ough (1964) reported that fermentations are relatively slow at 10 G/50 F compared with those conducted at 15°G/60°F or 27°G/80 F. Temperature also affects the population balance between Saccharomyces and non-Saccharomyces yeasts. In red wine fermentations (20°G/68°F to 30°G/86 F), Saccharomyces cerevisiae represents the dominant species (Sharf and Margalith, 1983), partially due to the warmer temperature of fermentation. At lower fermentation temperatures such as those used in white wine production, non-Saccharomyces yeasts can proliferate to yield much higher populations (Section 6.2.2). 

A typical bourbon fermentation continues for 72 hours at a fermentation temperature within the 31—35°C range. Many fermentation vessels are equipped with agitation and/or cooling coils that facHitate temperature control. Significant increases in yeast numbers occur during the first 30 hours of fermentation. Over 75% of the carbohydrate is consumed and converted to ethanol. Within 48 hours, 95% or more of the ethanol production is complete. 

Temperature, pH, and feed rate are often measured and controlled. Dissolved oxygen (DO) can be controlled using aeration, agitation, pressure, and/or feed rate. Oxygen consumption and carbon dioxide formation can be measured in the outgoing air to provide insight into the metaboHc status of the microorganism. No rehable on-line measurement exists for biomass, substrate, or products. Most optimization is based on empirical methods simulation of quantitative models may provide more efficient optimization of fermentation. 

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