Alcoholic fermentation sluggish/stuck fermentations

The success of an alcoholic fermentation depends on maintaining the population of viable yeast at sufficient levels until all the fermentable sugars have been fully consumed (Bisson 1999 Zamora 2004). Otherwise, the winemaker is faced with the serious problem of stuck and sluggish fermentations. The causes and the ways to avoid stuck and sluggish fermentations are discussed later (Bisson and Butzke 2000). 

Presence of medium chain fatty acids The presence of MCFA can decrease yeast viability and even stop alcoholic fermentation. This problem is more prevalent in white winemaking because fermentation is usually carried out at low temperatures and without any aeration. Yeast hulls have been very useful for avoiding this problem. Yeast hulls adsorb MCFA from the media and provide sterols and UFA to the yeasts. Yeast hulls can be used as preventives (20 g/hl) or as curatives (40-50 g/hl) of stuck and sluggish fermentations. 

Juice and wine pH play a mjgor role in the development of yeast and bacterial populations. Species respond differently in terms of growth rate as well as production of sensorially important metabohtes. In the case of Saccharomyces, growth and fermentation rates slow as pH decreases to near 3.0, concomitantly increasing the risk of sluggish or stuck fermentations. Kudo et al. (1998) found that the relative concentration of and H in a grape must plays an important role in successful completion of alcoholic fermentation, with a minimum of 25 1 being necessary. Whereas... 

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