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Most of the biological components of a fermenting substance are microorganisms, mainly yeasts and molds, which are in turn made up of many smaller structural and metabolic proteins (the latter falling into the more specific protein category of the enzymes). These organisms evolved in acidic conditions; therefore, their proteins have evolved to conform to their optimal shapes and functions in slightly acidic conditions. Moreover, a slightly acidic pH deters the formation of competing bacterial colonies, helping fermentation to proceed unobstructed. However, as environmental pH increases into moderate and high acidity (generally in the range of pH 6.0 and higher), proteins start to denature. There are a few exceptions to this pattern, usually where a low (basic) pH generates essential ingredients for a specific fermentation process.

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Fermentation is an anaerobic process in which sugar molecules are broken down into simpler molecules. Some of the commonly known products of the fermentation process are bread, beer, wine, etc.

The fermentation process is affected by a number of factors, including pH, temperature, nutrient concentration, and availability. Among the microorganisms, yeast and mold are acid-tolerant and prefer lower pH conditions for their growth. This means that fermentation by yeast and mold will be faster at lower pH values. In fact, the best pH range for yeast fermentation is 4.5-5.5.

One of the reasons, lower pH increases the fermentation rate is because the pH affects the shape of the enzymes (proteins) that help fermentation reactions. The amino acids that form the enzymes can be either acidic or basic depending on the functional group attached to them. It has been found that at lower pH, the acidic amino acids are present and that fermentation rate is faster as compared to higher pH conditions. In addition, it should be noted that most of the natural sugar from the fruits is generated in the acidic conditions. This means that yeast (and the associated enzymes for the fermentation process) have been naturally selected for working under the acidic conditions. And hence lower pH conditions are preferable for the fermentation process.

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