The formation of sulphur compounds in beer is a subject of great interest. Such compounds, especially sulphur volatile compounds (VSC), are essential for the aroma of beer (and some of them were identified as key compounds, i.e. dimethyl sulfide & dimethal trisulfide, in which they can play an attractive or a repulsive role (for example: accumulate sulphur atoms from the growth medium). Sulphur compounds essentially arise from common sulphur-bearing precursors such amino acids, i.e. methionine, which being the most commonly found, moreover, methionine repress the cysteine-induced increase in the H?S production but had no effect on the formulation of S02. Differences are also seen in H2S compared with S02 production in response to nitrogen levels in wort. However, biochemically H2S and S02 production are closely linked, environmental condition in brewery can have different effects on their rate of formation. These facts provide insights into possible opportunities to modulate the levels of H2S and S02 in industrial fermentations. Analyses on worts indicated that thioesters resulted from fermentation, whereas the polysulfides derive primarily from malt and hop. Changes in process conditions such as temperature, aeration, nutrient type and a variability as well as metabolite concentrations can significantly affect brewer's yeast metabolism during fermentation. Alterations in these factors serve to stress, which causes changes in the cellular composition that may either directly or indirectly impact on fermentative performance.
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