YEAST – Yeasts are single-celled microorganisms that grow and reproduce by budding. They are biologically classified as fungi, which are responsible for converting the fermentable sugars into the alcoholic beverage called beer. There are literally hundreds of varieties and strains of yeasts. Generally, there are two types of beer yeast: Ale yeast (“top-fermenting” type, Saccharomyces cerevisiae) or lager yeast (“bottom-fermenting” type, Saccharomyces pastorianus).
YEAST HEAD – The yeast-containing froth at the surface of top fermenting ale at the end of primary fermentation. It is sometimes recovered by skimming or suction to be used for pitching further worts.
YIELD EXTRACT – The percentage of extractable dry matter in the grist; i.e., the total amount of dry matter that passes into solution in the wort during mashing.