and water, or any suitable mixture, they grow and multiply, producing more yeast plants like themselves, and in growing they give out carbonic acid gas and water, with a little alcohol. Cooks talk about keeping a little yeast in sugar and water, but it is kept only as this year's corn is kept when it is sown to make next year's bread. It does not grow freely in sugar and water only, it requires something more. Flour and sugar is easy and convenient, or potatoes. The better the food suits the yeast the faster it grows; in some mixtures, carefully prepared on purpose, it grows so fast that as much as will lie on a shilling fills a cup in an hour or two. It must always be kept warm, at blood-heat, during the process of fermentation, unless you desire to check its growth or vigour, in which case the temperature must be considerably reduced.
Growth of Yeast.—One practical use of these facts is that, given a little good yeast, any amount more may be made. A second is, that if Brewer's yeast is bitter, a little of it will always yield some new yeast that is not bitter.
Rough usage or shaking will also prevent its growth,
Before making any quantity of bread, it is wise to test the yeast and see if it yields, by mixing a little and setting it near a warm stove for an hour, but on no account must it get hot, for that would effectually kill it.
Home-made Yeast is sometimes made of malt and hops, and no yeast is added by the maker. If the solution begins to ferment, yeast has certainly got into it some way or another, and yet, exposed to the air, it is almost sure to ferment sooner or later, and will probably ferment very soon if there is yeast anywhere near.
Choice of Yeast.—In this country the choice of yeast is almost unlimited, for besides Brewer's and Baker's "Patent," there is an immense quantity imported from the continent, and vast quantities are also supplied by the spirit factories or distilleries of this country. All kinds of leavening matter have, however, been, and are still used in different parts of the world: in the East Indies, "toddy," which is a liquor that flows from the wounded cocoa-nut tree; and in the West Indies, "dunder," or the refuse of the distillation of rum. The dough then undergoes the well-known process called kneading. The yeast produces fermentation, a process which may be thus described:— The dough re-acting upon the leavening matter introduced, the starch of the flour is transformed into saccharine matter, the saccharine matter being afterwards changed into alcohol, water, and carbonic acid gas. The dough must be well "bound," and yet allow the escape of the little bubbles of carbonic acid which result from fermentation, which in their passage cause the numerous little holes which are seen in light bread.
To Choose Flour.—The quality of wheat varies much with the weather of each season at home, and also with the weather and soil in countries that differ more from each other than our wettest season from our driest.
