Fermentation hydrogen sulfide production

Nevertheless, addition of bentonite at the beginning of the alcoholic fermentation may deplete the assimilable nitrogen content of the must due to electrostatic binding and adsorption. This may result in fermentation sticking and/or hydrogen sulfide production. Addition of an exogenous source of nitrogen eliminates these potential problems. 

Thomas, C. S., Boulton, R. B., Silacci, M. W., Gubler, W. D. (1993) The effect of elemental sulfur, yeast strain, and fermentation medium on hydrogen sulfide production during fermentation. American Journal ofEnology and Viticulture, 44, 211-216. 

Principal characteristics C. intermedius cultures fail to produce HgS in TSI agar, but hydrogen sulfide production is detectable on more sensitive media such as FeClg gelatin or Pb acetate agar lysine is never decarboxylated. About 20 per cent of strains produce indole and 40 per cent ferment sodium malonate [21, 88]. 

Rankine (6, 38) believes that the differences in the secondary products formed in wines during fermentation by various yeasts are quantitative rather than qualitative, and careful selection of pure yeast strains can eliminate wine disorders caused by large amounts of undesirable by-products such as hydrogen sulfide, mercaptans, acetaldehyde, acetic acid, ethyl acetate, higher alcohols, etc. 

Among the oenological yeasts added during alcoholic fermentation, some strains of S. cerevisiae can use organic compounds to produce hydrogen sulfide and sulfites or the intermediate product of methionine (Zambonelli, 1988). These strains can use other sulfur-containing molecules, such as several of the pesticides employed in viticulture. 

Fining also may be done to juice prior to fermentation. Protein fining agents may be used to reduce phenolics in press juice, or bentonite used for protein reduction or reduction of potential for hydrogen sulfide (H2S) production (18). 

Effect of Yeast on Fermentation. North Coast enologists recognize the important effects yeast strains have on the management of the fermentation, its evenness and completion, and the wine composition. Rankine (23) reviewed the different effects of yeast strain on wine composition and noted especially the relationship of yeast strain to sulfur dioxide, hydrogen sulfide, and acetaldehyde production. 

Seasonal Variation in the Production of Hydrogen Sulfide During Wine Fermentations... 

Fig. 1.8 Asaccharolytic fermentation produces ammonia and short-chain fatty acids. This group of fermentations by oral bacteria utilizes proteins, which are converted to peptides and amino acids. The free amino acids are then deaminated to ammonia in a reaction that converts nicotinamide adenine dinucleotide (NAD) to NADH. For example, alanine is converted to pyruvate and ammonia. The pyruvate is reduced to lactate, and ammonium lactate is excreted into the environment. Unlike lactate from glucose, ammonium lactate is a neutral salt. The common end products in from plaque are ammonium acetate, ammonium propionate, and ammonium butyrate, ammonium salts of short chain fatty acids. For example, glycine is reduced to acetate and ammonia. Cysteine is reduced to propionate, hydrogen sulfide, and ammonia alanine to propionate, water, and ammonia and aspartate to propionate, carbon dioxide, and ammonia. Threonine is reduced to butyrate, water, and ammonia and glutamate is reduced to butyrate, carbon dioxide, and ammonia. Other amino acids are involved in more complicated metabolic reactions that give rise to these short-chain amino acids, sometimes with succinate, another common end product in plaque.

Hydrogen sulfide and methanethiol are directly produced by yeast metabolism. The production of H2S during alcoholic fermentation is controlled by the enzymes responsible for reducing sulfates and biosynthesizing certain sulfur amino acids (cysteine and methionine) (Figure 8.19). Methanethiol is synthesized by yeast from methionine (De Mora et al., 1986). 

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