Fermentation sluggishness

Ethyl acetate, added prior to fermentation in amounts up to 3%, caused delays in the onset of fermentation proportional to the amount added, but once begun, the fermentation rate was unaffected. When the same levels of ethyl acetate were added to an active fermentation, the fermentation period was sluggish. 

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). 

For this reason, the lack of enough BAN can make the yeast use sulphur amino acids (cysteine and methionine), thus releasing hydrogen sulphite and mercaptans. Thus, supplementing with ammonium salts is recommended not only to avoid stuck and sluggish fermentations but also to prevent reduction off-odours (Jiranek etal. 1995). 

The causes of stuck and sluggish fermentations have been the subject of several studies (Larue et al. 1982 Ingledew and Kunkee 1985 Alexandre and Charpen-tier 1998 Bisson 1999). Some of them have already been described in previous points. The following list summarizes the possible causes and solutions of stuck and sluggish fermentations. 

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. 

Alexandre, H., Charpentier, C. (1998) Biochemical aspects of stuck and sluggish fermentation in grape must. J. Ind. Microbiol. BiotechnoL, 20, 20-27. 

Ingledew, W.M., Kunkee, R.E. (1985) Factors influencing sluggish fermentations of grape juice. Am. J. Enol. Vitic., 36, 65-76. 

Kunkee, R.E. (1991). Relationship between nitrogen content of must and sluggish fermentation. In Proceedings of the International Symposium of Nitrogen in Grapes and Wine, 18-19 de Juny de 1991, Seattle, Washington (pp. 148-155). Davis CA American Society of Enology and Viticulture. 

Sablayrolles, J.M., Dubois, C., Manginot, C., Roustan, J.L., Barre, P. (1996). Efectiveness of combined ammoniacal nitrogen and oxygen additions for completion of sluggish and stuck fermentation. J. Fermen. Bioeng., 82, 377-3S1... 

Several treatment agents of wine yeast cell walls, sodium caseinate, gelatin, bentonite were evaluated for their potential to bind with aroma compounds. The loss of sensory properties of wine, especially flavor modification, is partly caused by protein stabilization treatments with fining agents or ultrafiltration processing of wine (IS 14). Yeast cell walls are used in sluggish or stuck wine fermentation the effect on fermentation has been explained by the adsorption of toxic fatty acids present in the growth medium (15). Therefore yeast walls are also assumed to bind aroma compounds. 

Huang, Y.C., Edwards, C.G., Peterson, J.C., and Haag, K.M. 1996. Relationship between sluggish fermentations and the antagonism of yeast by lactic acid bacteria. Am. J. Enol. Vitic. 47, 1-10. 

Monteiro, E.E. and Bisson, L.F. 1991a. Biological assay of nitrogen content of grape juice and prediction of sluggish fermentations. Am. J. Enol. Vitic. 42, 47-57. 

Practical applications of alginates concern mainly secondary fermentation inside the bottle in sparkling wine production for easy clarification and removal of cells Other applications are the treatment of sluggish and stuck fermentations ... 

Silva S., Ramon P.F., Silva R, Maria de Fatima T. and Strehaiano P. Use of encapsulated yeast for the treatment of stuck and sluggish fermentations. Journal International Des Sciences De La Vigne Et Du... 

One of the earliest unconfirmed examples of an ABE fermentation phage infection concerned an abnormal fermentation at the CSC plant in Terre Haute, USA, using maize mash as substrate for a C. acetobutylicum strain [32]. In this instance, the sluggish fermentation lasted for about 1 year and halved the solvent yield. CSC expended considerable efforts into the investigation of the cause of this abnormal fermentation performance and developed a number of countermeasures for preventing its recurrence. These included the use of phage-immunized clostridial... 

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