Yeasts are fungi essential to the making of alcoholic beverages. The conversion of sugar by yeast into carbon dioxide and ethyl alcohol is called fermentation and involves yeast cells eating sugar and then excreting alcohol and carbon dioxide. The carbon dioxide forms the carbonation in beers and ales, and the alcohol slowly kills the yeast cells.
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Fermentation and Brewing
Alcoholic fermentation begins with a large-scale production of yeast cells. Over 24 to 28 hours -- for normal home-brewing, yeast present in the brew will consume oxygen and double their population every four hours. After consuming all of the oxygen, the yeast turn to the eating of sugar and the excretion of ethyl alcohol. The sugar used in brewing must be fermentable in order to produce alcohol. Certain malts used for brewing contain non-fermentable sugars that remain in the brew and balance the bitterness of the hops.
Temperature is another important factor regarding the yeast's ability to produce alcohol, with heat being a natural by-product of alcoholic fermentation. A temperature greater than 27C will kill the yeast and a temperature below 15C will slow production of alcohol and possibly stop fermentation.
Brewer's yeasts are especially cultured for beer brewing. Flimsy as far as yeasts are concerned, they tolerate only 5 to 6 per cent alcohol before dying. A single-celled fungus called Saccharomyces cerevisiae is used to make brewer's yeast.
A vital source of nutrients and minerals -- specifically B-complex vitamins, chromium and selenium -- brewer's yeast is also grown to make nutritional supplements.
Ale yeast can tolerate a much higher concentration of alcohol than regular brewer's yeast. Specific types of ale yeasts are cultured and sold, which include the highest variety of ale that can be found in online databases. Most of these special yeasts can survive in brews with concentrations from 8 to 15 per cent alcohol.
Ale yeasts are expensive speciality yeasts. Novelty yeasts like ale yeasts are for serious home brewers with money to spend.
The ancient tradition of winemaking probably started by accident; human cultures have cultivated grapes for their juice -- and vitamin content -- because grapes are delicious. Grape juice already contains the exact levels of acids, tannin, sugar and nutrients needed for winemaking. Grape juice ferments by itself over time; wine is slowly made by the yeast already present in the grape juice. After adding wine yeast, sugar may be added gradually as fermentation goes on to produce a higher alcohol concentration in the end product.
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