Initiation of fermentation

In live cocoa seeds, the methylxanthines are localized in polyphenolic storage cells. Bean death, which occurs 24 to 48 h after initiation of fermentation, triggers diffusion of the methylxanthines from the nib to the shell. The early studies of Humphries state that cacao cotyledons lose about 40% of their theobromine during fermentation.17 According to Knapp and Wadsworth, the loss of theobromine and caffeine becomes significant on the third day when the methylxanthines begin to diffuse into the shell.18 This migration continues until the concentration of the methylxanthines in nibs and shell are almost equal. 

Fig. 3.3. Example of a theoretical activation of grape must fermentation (Sq initial sugar content Si sugar content at the end of fermentation). (I) Control fomentation stops, leaving unfermented sugar (So — Si), (n) Activation at the initiation of fermentation, but the completion of fermentation in musts having high sugar concentrations is not improved. (Ill) Activation acting on yeast population growth and survival fermentation is complete...

The timing of the addition of ammonium salts appears to be important. Ribereau-Gayon et al. (1975a) had suggested their addition in must before the initiation of fermentation. Yeasts... 

Alcohol addition (% vol.) Delay for initiation of fermentation Yeast population (10 /ml) Alcohol content attained (% vol.) Alcohol formed (% vol.) Residnal sngar (gd) Nitrogen assimilated (mg/1) Glycerol (mmol/1)... 

The experiment in Table 3.6 shows the effect of the addition of alcohol to grape must. It slows the initiation of fermentation and limits the assimilation of nitrogen and the formation of alcohol. Yet the yeasts can continue their activity up to a higher alcohol content, as long as the inhibitory action of ethanol is not excessive. In this experiment, the variation of the glycerol concentration represents significant metabolic modification. As seen in Section 3.4.1, ethanol intensifies the inhibitory effect of an elevated sugar concentration in must. 

In addition to its influence on yeast activity, temperature affects fermentation speed and limits. Between 15 and 35°C, the duration of the latent phase and the delay before the initiation of fermentation become shorter as the temperature increases. Simultaneously, yeast consumption of nitrogen increases (Section 3.4.2). 

Temperature Initiation of fermentation Alcohol content attained (% vol.)... 

Must clarification before the initiation of fermentation has long been known to affect the quality... 

Many stuck fermentations result from winemaking errors. Moreover, systematic stuck fermentations have been observed in certain wineries year after year. They disappear without any apparent reason at the same time that the winemaker changes. More often than not, the necessary operations are known but not carried out properly. In red winemaking, stuck fermentations often result from excessive temperatures at the initiation of fermentation and a poor control of tank temperature during... 

When conserved intact after its harvest, the grape still maintains an intense physiological respiratory activity—which is utilized during drying. The lack of oxygen and the depletion of available respiratory substrates rapidly provoke the initiation of fermentative processes in the berry. 

A cool year or cool climate is characterized by a late and often insufficient maturity. Grape acidity is elevated and the musts are thus relatively protected against bacterial attack. However, there is a risk of botrytis attacks and the formation of oxidasic casse, since cool climates often correspond to rainy climates. In addition, grape crops arriving at the winery are often characterized by relatively low temperatures in cool years. As a result, the initiation of fermentation can be difficult, even more so when the grapes are washed by rain the natural yeast inoculation can be insufficient. 

Whatever the heating method used, it is recommended that the must or crushed grapes should be cooled before the initiation of fermentation, which must take place at approximately 20°C. Excessive production of volatile acidity by yeasts can hopefully be avoided. 

Different clarified juices must often be assembled when filling a high-capacity fermenting tank. This operation requires several elementary precautions. Before blending the clarified juices from different tanks, fine lees which have settled after racking must be reincorporated into the juice. In addition, juice that has not initiated fermentation should not be blended with fermenting juice, since the yeasts fermenting one juice produce H2S in the presence of free SO2 from the other juice. The initiation of fermentation must occur after the constitution of the blend. 

Depending on the legislation, various adjustments such as the addition of sugar or modification of acidity can be made to juice before the initiation of fermentation. These adjustments should be limited to avoid disequilibrating the wine. 

Cocoa bean fermentation is a mixed-culture process, consisting initially of fermentations by yeast and lactic acid bacteria followed by oxidation of the fermentation products ethanol and lactic acid into acetic acid and acetoin by several Acetohacter strains, of which /I. pasteurianus is the prominent one (Moens et al. 2014). A C-based carbon flux analysis of Acetohacter during cocoa pulp fermentation-simulating conditions revealed a functionally separated metabolism during co-consumption of ethanol and lactate. Acetate was almost exclusively derived from ethanol, whereas lactate served for formation of acetoin and biomass building blocks. This switch was attributed to the lack of phosphoenolpyruvate carboxykinase and malic enzyme activities, which prevents conversion of oxalo-acetate and malate formed by acetate metabolism in the TCA cycle to PEP and pyruvate and subsequently to acetoin (Adler et al. 2014). Lactate, on the other hand, can be converted to pyruvate, which is then used for acetoin formation or, after conversion to PEP by pymvate phosphate dikinase, for gluconeogenesis. The inability of conversion of TCA cycle intermediates to PEP resembles the situation in G. oxydans, where in addition no enzyme for conversion of pyruvate to PEP is present. 

---