Yeast is a minute, single-celled fungus, which exists in soil and on fruit. Yeast is used both as a raising agent and as an agent of fermentation, and is consequently cultivated and its properties utilized in the baking of BREAD and brewing of
In order to activate yeast into growth, the addition of carbohydrate – in the form of sugar – liquid and warmth, in correct proportions, are necessary. Excess of sugar, cold, fat or salt will retard growth, while excess of heat will kill the plant altogether. (This happens during the baking of bread but by that time the yeast has done its work.) . As the yeast grows a ferment is produced which breaks down the carbohydrates and converts them into carbon dioxide which causes the dough to rise.
The three main types of yeast most commonly available are fresh and dried yeast for baking and brewer’s yeast. Fresh yeast is moist and crumbly in appearance and is preferred by some people to dried yeast. Fresh yeast is obtainable from specialist food stores and bakeries where the bread is made on the premises, and may be kept, well wrapped in the refrigerator, for 2 to 3 days. Fresh yeast may be frozen, if it is correctly wrapped, for several months.
Dried yeast is a concentrated form of fresh yeast and is available from most food stores in tins and packets. Providing the container is airtight, dried yeast will keep for up to 6 months.
Delicious crispy-topped potatoes, Yeaman’s Spiced Potatoes make a marvellous supper or lunch dish for a cold winter’s day.
If substituting dried yeast in a recipe which specifies fresh, use only half the quantity and follow the directions on the tin or packet on how to prepare it.
Brewer’s yeast is weak and semi-liquid, and is mainly used in the brewing of beer and ale. In addition, a special form of yeast is used in making wine.
When making bread or bun mixtures with yeast, where no fat is used, ounce of fresh yeast will raise up to 1 pound of flour, and 1 ounce of fresh yeast up to 3 pounds of flour. For richer mixtures containing fruit and fat, more yeast is required.
Yeast is a good source of all the vitamins of the B group. As well as being used in baking, brewing and wine-making it is also sometimes prescribed medicinally, usually in the form of yeast tablets or concentrated yeast extract.