Fermentation Difficulties

200mg/L, although these concentrations may not be sufficient to achieve the desired degree of fermentation (Lafon-Lafourcade et ah, 1979). Permissible addition levels of nitrogen in the United States are considerably higher (Section 8.2). 

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Excessive temperatures and sugar concentrations can provoke sluggish or stuck fermentations. Nutritional deficiencies and inhibition phenomena can also be involved. All of them have either chemical or physicochemical origins. Fermentation kinetics can be ameliorated by different methods which influence these phenomena. Early action appears to increase their effectiveness yeasts in their growth phase and in a medium containing little ethanol are more receptive to external stimuli. The winemaker should anticipate fermentation difficulties the possible operations are much less effective after they occur. 

More specifically, the preliminary development of yeasts, lactic bacteria or Botrytis cinerea can hinder the alcoholic fermentation process. In the case of alcoholic fermentation difficulties, bacterial growth and malolactic fermentation exacerbate these difficulties. Stuck fermentations often result (Sections 3.8.1 6.4.1). 

Clarification essentially modifies must ferment-ability. Clear must is kuown to ferment with more difficulty than cloudy must (though the elimination of yeasts is not the only reason for this fermentation difficulty, as was once thought). Yet clarification simultaneously favors the aromatic finesse of the wine. White wine quality is thought to be enhanced by a somewhat difficult and slow fermentation. In general, all operations that... 

Sections 13.5.2 13.5.3). For vineyards in the Bordeaux region, a turbidity of less than 60 NTU can lead to serious fermentation difficulties. Above 200 NTU, the risk of olfactive deviations due to the presence of must lees is certain. 

After a botrytis attack, grapes and must contain polyosides with phytotoxic and fungistatic activities. B. cinerea also produces divers antibiotic substances botrytidial, norbotryal acetate and botrylactone. Some of these substances can be the source of fermentation difficulties. 

Fermentations in the presence of stems are always qnicker and more complete (Figure 12.4). The stem facilitates fermentation not only by ensnring the presence of air bnt also by absorbing calories, Umiting temperature increases. Fermentation difficulties are rarely encountered with stenuned grapes. 

At the end of alcoholic fermentation, malic acid concentrations should be determined and monitored if necessary. Malolactic fermentation (MLF) normally occurs after the complete depletion of sugars. An early initiation of MLF is generally linked to alcoholic fermentation difficulties and insufficient sulfiting. In certain cases, the two fermentations take place simultaneously, even though the antagonistic phenomena between yeasts and bacteria tend to inhibit alcoholic fermentation. 

Another characteristic of wines made from grapes affected by noble rot is their relatively high volatile acidity level. Its origin can be accidental, due to the presence of lactic acid bacteria in juice and especially acetic acid bacteria on grapes. Yeasts also form some volatile acidity, due to the corresponding fermentation difficulties of these juices (Section 2.3.4). 

Liquefaction. Siace the 1970s attempts have been made to commercialize biomass pyrolysis for combiaed waste disposal—Hquid fuels production. None of these plants were ia use ia 1992 because of operating difficulties and economic factors only one type of biomass Hquefaction process, alcohohc fermentation for ethanol, is used commercially for the production of Hquid fuels. 

Difficulties encountered in the separation and stabihty of the individual rifamycins led to studies to increase the yield of individual components of the complex. The addition of sodium diethylbarbitutate to the fermentation medium of N. mediterranei resulted in the formation of rifamycin B as practically the only substance formed (91,92). 

The potential usefulness of elfamycins as growth promoters and feed-conversion enhancers is now generally recognized. Low original fermentation yields and difficulties in yield improvements discouraged early attempts to develop aurodox ( 1, R = CH ) and mocimycin (kirromycin) (1, R = H) commercially. 

Despite the similarities of their structures, cellobiose and maltose have dramatically different biological properties. Cellobiose can t be digested by humans and can t be fermented by yeast. Maltose, however, is digested without difficulty and is fermented readily. 

Continuous SO3 single-pass sulfonation processes, 23 543-552, 550 Continuous solution polymerization, reactors used for, 23 394-395 Continuous steel casting, 23 266-270 difficulties of, 23 266-267 universality of, 23 269-270 Continuous sterilization, in fermentation, 11 35-36... 

Fermentation systems obey the same fundamental mass and energy balance relationships as do chemical reaction systems, but special difficulties arise in biological reactor modelling, owing to uncertainties in the kinetic rate expression and the reaction stoichiometry. In what follows, material balance equations are derived for the total mass, the mass of substrate and the cell mass for the case of the stirred tank bioreactor system (Dunn et ah, 2003). 

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