A microscopic living fungus that multiplies rapidly in suitable conditions. It is an essential ingredient for breadmaking and brewing. When mixed with warm water, sugar and flour, yeast produces carbon dioxide, which causes dough to rise.
There are three types of yeast used in bread-making: fresh yeast (also known as cake or compressed yeast), which is a firm, moist cream-coloured block stored in the refrigerator. Dried yeast (or active dried yeast) comes in small granules that are first reconstituted with warm water and sugar; and powdered (or ‘easy-blend’ or ‘fast-action’) dried yeast which is sold in sachets and just sprinkled straight into a bowl of flour.
Store the different types of yeast carefully according to the packet instructions because they won’t work if they become stale. Fresh yeast must be refrigerated and will become inactive quite rapidly - about one to two weeks. Fresh yeast can also be frozen and will keep for up to three months. Dried yeast can be kept at room temperature for months, but do use before the date specified on the packet.