Yeast


Yeast -

Is the family name of those tiny plants or micro-organisms belonging to the Fungi class which reproduce themselves by budding. There are many varieties, but they are all oval or round, colorless and nearly transparent, except when great numbers are bulked together, and so small that singly they cannot be discerned by the naked eye. The mature plant or cell develops a bud which rapidly increases in size and detaches itself from the parent plant, to itself bud and develop another cell - and so on indefinitely. The new cell frequently commences to bud before it detaches itself from the parent plant, and the latter may produce a second bud before the first is detached - resulting often in the formation of clusters of several cells before disintegration. The multiplication is very rapid where the food supply is favorable.

Yeast plants are present everywhere. They flourish best in foods containing sugary solutions in moderate amount, or substances convertible into sugar, but sugar itself is immune, except some moist varieties such as maple sugar. Thus in the household they will speedily multiply in the jelly that is left exposed in a warm room and cause it to ferment, but they cannot grow in the dry sugar nor in the heavily sugared jam standing at its side.

These "wild" Yeast cells must be kept out of food, for their uncontrolled, unregulated growth often spoils it by producing undesired fermentation. The cultivated Yeast plant is, on the other hand, one of the most valuable of human food assistants.

The usefulness of properly controlled Yeast is found in the fact that the action of its "enzymes" or secretions on the sugary contents of the matter, whether bread dough or grape juice, etc., in which it falls or is placed, is to convert the sugar into alcohol and carbon-dioxide (carbonic acid gas). Of these two, only the alcohol is retained in still wines, spirits, etc., but sparkling wines, Beer, etc., include also a small amount of the carbon-dioxide. In bread making, the alcohol, comparatively unimportant in quantity and effect, is lost by evaporation in baking. The carbon-dioxide also passes away in the oven - but in the dough set to rise, it produces the hundreds of little bubbles or cavities which give the load the desired porous character (see article on bread).

Another good example of the action of Yeast is seen in the home manufacture of root Beer and similar beverages. The extract purchased provides the agreeable herb flavor, but the directions for making require the addition of both Yeast and sugar, and it is the action of the Yeast on the sugar which gives the slightly exhilarating quality (from the small percentage of alcohol produced) and the effervescence (from the action of the carbon-dioxide).

It is the wild Yeast in grape and apple skins which produces the bulk of our wine and cider, by causing fermentation in the juice of the grapes and apples, but with these exceptions nearly all the Yeast plants utilized are those of carefully selected, specially cultivated varieties. The fermentative process which precedes the manufacture of whisky, rum, etc., is always produced by cultivated Yeast. bread dough, if left to stand in a warm room, will generally "rise," as a result of the activity of the wild Yeast which has fallen in it, but the results are uncertain and irregular compared with those obtained by the use of cultivated Yeast.

Yeast grows most freely between 70° and 95° Fahr., so the temperature of a good refrigerator will prevent propagation. Food in which wild Yeast has begun to grow, but in which it has not progressed sufficiently to do considerable damage, can be saved by Boiling, or its equivalent heat in other forms of cooking. Heat is the only effective destroyer. It must be remembered, however, that unless the food thus freed is effectually covered or placed in a refrigerator, it is just as liable as before to suffer fermentation from new wild Yeast getting into it.

Cultivated Yeast consists of selected wild cells, propagated in appropriate food material. If undisturbed, they will multiply until the whole is a mass of practically pure Yeast. Different kinds are grown for special purposes; as a variety which may be very good for Beer, for example, may not be desirable in color or taste for bread.

Commercial Compressed Yeast is obtained from distillery fermenting vats by skimming or separating from the "wort" and then cleansing, etc., or by sowing selected Yeast cells in vats filled with a mixture of malt and rye or corn, or boiled potato mash, etc., and water, held at a moderately warm temperature. Boiling the water with a small quantity of hops, followed by straining, frequently precedes the addition of the malt or potato mash, partly for the agreeable flavor but principally to retard the growth of any bacteria present. As the cells multiply, they collect in a thick coating on the surface. This is skimmed off from time to time, washed, freed from part of the water and made into the soft, rather soggy cakes sold in such enormous quantities for both household and bakers' use. When fresh, nearly all the cells will be found alive and vigorous - there are millions of them in each cake, mixed with starch, etc. - but after two or three days many of them die and the Yeast will show less and less vigor. In time, bacteria, another form of micro-organism, will develop in the cake and spoil its flavor. It is consequently best to use Compressed Yeast while perfectly fresh. If this is impossible, its life may be prolonged by placing the cakes in cold water and setting in the ice chest. It should never be exposed to tempeerature below the freezing point.

Next after Compressed Yeast in strength and utility for bread making, is Brewer's Yeast, the brownish frothy top Yeast from the fermenting vats of ale or Beer. It answers the same purpose, but is not so vigorous, and sometimes gives a slightly bitter taste.

Beer Yeast is also used to a limited extent by physicians. It makes an appetizing "Bouillon," somewhat resembling beef tea, and is given as a stimulant in low fevers when inflammatory symptons make the use of wine inadvisable.

Dried Yeast, in cakes or powder, is Compressed Yeast dried at low heat. The process kills some of the plants and thus lessens the vigor of the Yeast, but a good many are left in a dormant condition and the advantage is that it will, under suitable conditions, keep for several weeks, and sometimes months. It must, however, be handled with care, as its vitality is destroyed or lessened by falls, bruises, etc., and by excessive heat or cold.

The live cells of Dried Yeast begin growing again when moistened. The best plan is to put the cake or powder in a little sweetened warm water shortly before using.

Both Compressed and Dried yeasts vary in purity and hence in value, so that it is advisable to purchase from concerns of recognized experience and integrity.


Arround Yeast in The Grocer's Encyclopedia


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