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Yeasts for Home Brewing
Yeast is a natural single-celled microorganism that multiplies by reproducing itself when suitable conditions are in place
In homebrewing, yeasts are responsible for converting fermentable sugars into alcohol.
There are hundreds of varieties and strains of yeast.
Use top-fermenting yeasts for brewing ale stouts, Kölsch,s, Altbier, porters, and wheat beers.
The temperatures needed for Ale yeasts to ferment ranges from 10 to 25°C. However, some strains will not actively ferment below 12°C (33).
Ale Yeast which is commonly called top or surface fermenting yeasts due to the yeast rising to the top during use. The yeast rising to the surface creates a rich very thick yeast head.
That is where the term "top-fermenting" comes from with ale yeasts.
Using ale yeasts at these warmer temperatures produces a beer high in esters, which most regard as the distinctive character of ale beers.
Some of the styles of lager made from bottom-fermenting yeasts are Dortmunders, Bocks, Märzen, Pilsners, and American malt liquors.
The best use of a Lager yeast strains is at temperatures ranging from 7 to 15°C.
At these lower temperatures, lager yeasts do not grow as fast as ale yeasts and do not produce as much surface foam; the yeast tends to settle out at the bottom of the fermenter as fermentation nears its end.
The final flavour of the lager will depend on the strain of lager yeast and the temperatures at which it was fermented.