Fermentations speed

As an alternative to detoxification methods, improvement in P. stipitis ability to grow and ferment in acid-pretreated slurries (through conditioning or adaptation) have been pursued in some studies [ 16-18]. To our knowledge, there has been no study on how aeration (agitation) affects the improvements in fermentation observed fixrm adaptation. This study looks at how aeration (agitation) affects fermentation speed in adapted and unadapted strains of P. stipitis. 

The fermentation results for the wild stains and liquid-adapted strains of P. stipitis on 12.5% hydrolyzate at 150 rpm rotation speed are shown in Fig. 3. The difference in fermentation speed between the wild and hquid-adapted strains were minimal at 150 rpm. The presence... 

Automated control systems should be linked to fermentation speed and therefore yeast activity, a parameter certainly as important as the temperature. When the speed of CO2 production exceeds a previously established limit, the obtained temperature should be maintained. As soon as the speed decreases, the apparatus should let the temperature rise in order to revive the fermentation. This operation would permit the fermentation to be completed more quickly. Temperature modulation should be related to must fermentabiUty. Simultaneously letting the temperature increase would result in a decrease in the total energy demand (Table 3.1). Of course, the apparatus should maintain the temperature within compatible enological limits. 

Fermentation kinetics are directly linked to the growth cycle. The fermentation speed is at its maximum and practically constant for... 

Although complex mixtures of ammonium salts and amino acids are more effechve for promoting yeast growth and fermentation speed, ammonium salts are used almost exclusively to increase... 

Other sterols and long-chain fatty acids share most of the properties of ergosterol. Some are constituents of grape bloom and cuticular wax, such as oleanoUc acid—especially when associated with oleic acid (Figure 3.5). These constituents explain the results of past experiments, indicating an acceleration of the fermentation speed of grape must in complete anaerobiosis when grape skins and seeds were added in suspension. 

Atmosphere Additions Nitrogen utilization (mg of FAN/1) Number of cells (xlO /1) Fermentation speed (g of sugar per 100 ml/24 h)... 

The presence of ethanol at the time of inoculation prolongs the latent phase and reduces cellular multiplication. An elevated temperature increases this inhibitory action. This effect of ethanol on yeast growth and fermentation speed occurs even at low concentrations from the start of fermentation. The difficulty of restarting a stuck fermentation is, therefore, understandable. 

The fermentation speed, which depends on must composition (nitrogen-based substances) and yeast inoculation conditions. Operations such as aeration, chaptalization and inoculation will increase the fermentation speed, limit the dissipation of calories and increase the maximum temperature. Reciprocally, not crushing the red harvest in carbonic maceration (Section 12.9.1) will slow fermentation kinetics and lower the maximum temperature. 

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). 

The impact of temperature on fermentation is depicted in Figure 3.8. The latency time decreases and the initial fermentation speed increases as the temperature rises. The risks and severity of a stuck fermentation also inaease with temperature. Of course, if the initial sugar concentration had been lower in this example, the fermentation would have been complete at 35°C. On the other hand, a higher sugar concentration would have resulted in a stuck fermentation even at 25°C. This shows that fermentation speed increases as the temperature rises but that the fermentation is also increasingly limited. 

Fig. 3.8. Influence of temperature on fermentation speed and limit (So = initial sugar concentration). At 25°C, fermentation is slower, but complete. At 30°C, and especially 35°C, it is more rapid, but stops at fermented sugar concentrations Sj and S2, respectively, below So...

Complete anaerobiosis does not permit satisfactory yeast activity (growth and survival). Aeration increases fermentation speed. It must take... 

Along with pH, temperature is certainly the factor that most strongly influences the malolactic fermentation speed of a properly vinified wine not excessively sulfited. This factor is also the most easily monitored and controlled. 

Sulfiting also makes use of the stimulating effect of sulfur dioxide when used in low concentrations. Consequently, the fermentation speed accelerates, as shown by the curves in Figure 8.8. After an initial slowing of the fermentation at the start, the last grams of sugar are depleted more rapidly. Finally, the fermentation is completed more rapidly in the lightly snlfited mnst. 

The juice is aerated and it is inoculated by yeasts. The fermentation is quicker and the temperature higher. In certain circumstances, a slower fermentation speed and lower temperatures can be obtained through not crushing (carbonic maceration. Section 12.9.4). 

Lactic acid bacteria growth is optimum at a pH between 4.2 and 4.5. In the pH range of wine (3.0-4.0), malolactic fermentation speed increases with the pH. The pH limit for growth is 2.9 but even at 3.2 bacterial growth is very limited. Malolactic fermentation becomes possible at a pH of 3.3 or higher. 

Maceration increases the amino acid concentration in juice, resulting in an improved fermentation speed, which is often observed in practice. Macerated grapes also produce juice and wine that is richer in neutral polysaccharides (Table 13.10) and proteins than pressed whole clusters. Wines made from macerated grapes... 

The first steps of winemaking with maceration consist of moderately crushing and destemming the grapes. The grapes are then transferred to the tank and sulfited at 5-10 g/hl. The fermentation temperature is set at approximately 30°C to favor maceration. Maceration times vary from 2 to 8 days, if the fortification occurs after must separation. In this case, the fermentation speed should be reduced beforehand. Wines are macerated for 8 to 15 days when continuing the maceration after fortification. 

---