The biggest contributors to the final flavor of the fermented or distilled product are the strain of yeast selected and how that strain is treated during the fermentation.
Different strains of yeast make different congeners in widely different quantities. They also have very different responses to temperature, presence of specific nutrients, oxygen levels, etc. There is a considerable amount of information available about yeast strains and varieties, in books and magazines as well as from the yeast suppliers. It's a very good idea to get as much of this information as possible and to use it carefully when planning a production run for a particular product. Some sources of this information are listed in Appendix 8.
Home-brewing clubs frequently experiment with this phenomenon. In these experiments, a large batch of wort is made and prepared for fermentation, and separated into several carboys, each of which is inoculated with a different yeast strain. After completion, a tasting is held to compare the results. The differences can be staggering. Similarly, a single strain of yeast might be utilized at a variety of temperatures, with results ranging from a very crisp, "lager-like" beer produced at low temperatures to an extremely fruity, "estery" brew at higher ones.
Different strains of yeast also have very different temperature and alcohol tolerance levels. All yeast will die at some level of alcohol concentration, and this tolerance level drops as the temperature rises. Baking yeast, for example, dies off quite quickly when alcohol levels reach about 6-7 %, rendering it useless for making beverage alcohol. Most strains of Beer Yeast can tolerate 8-10% alcohol, though some can take more. Wine Yeast strains generally can ferment up to 14-15%, and a few can go as high as 20%. Adding large quantities of the wrong yeast will only make it reach its tolerance point faster, it will not result in a higher final alcohol concentration. There are hundreds of different strains of wine, beer and specialty yeast available from a large number of suppliers. Matching the strain to the desired product will greatly improve the success of your fermentations.
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