Yeast A mould consisting of single living cells, each capable of producing the enzyme Zymase which ferments carbohydrates to alcohol and carbon dioxide. Added to the wort in the Washback, the yeast multiplies, feeding on the sugars in the solution and producing alcohol which eventually kills it.
Yeast Mash (US term) When jug yeast is grown in dona tubs, cooked grains, known as yeast mash, are usually used as the growing medium. A yeast mash may be 'sweet' or 'sour'. The introduction of hops into this process produces a 'hopped yeast mash', and is not usually soured.
Yeast Tank The yeast tank is where the various types of yeast are blended together with a little hot water prior to their immediate addition (pitching) into the wort in the Washback.
Yield The amount of alcohol produced from a given quantity of barley. Originally measured in proof gallons (of alcohol) per bushel (of barley), a figure of 2.9 was considered very good.