The Birmingham age-herald., 1924-02-25
.ELRESIDE SCIENCE.
By RANs0ME SUTTON

Yeast is very lowly plant--not an animal nor an inert substance. It IS very prevalent in the air, and is the principal cause of fermentation in liquids, especially in liquids contain ing a trace of sugar.
 When any liquid containing fruit juice IS left exposed to warm air. yeast spores find their way into it, Then it begins to cloud, & scum forms over the surface, sediment settles to the bottom, bubbles of gas rise and burst-this is fermentation. As soon as fermentation ceases, the liouid clears, and experienced persons are able to defect in it a taste of alcohol. No longer is the liquid what it was Defore-it has been changed by yeast into something else.
 The diameter of a yeast organism IS only about one-three- -thousandtb part of an inch--a tiny sac of plant protoplasm, capable of independent existence and of rapid reproduction. II thin sample or scum be spread on glass slide, microscope of low power shows it consists of yellowish cells, existing singly or in. chains, aiioat in clear liquid. Each chain Of cells IS composed of the mother cell and such of the daughters as have not broken away.
 TO understand what takes place durlng fermentation it is necessary to know something about enzymes, a new word for recently discovered substance not very we'll understood bv chemists, though they know what it does. Enzymes are nitrogenous bodies produced by yeast cells, and their work is to break down the molescules Of liquids, then build up other kinds
 of molecules without themselves being affected by the breaking down and building up process. The action of an enzyme may be likened to that of A mouse. If mouse runs into a room where groups of women are standing, the groups instantly break up and new groups are formed. The excitement among the women is analogus to the fermentation in the liquid. Enzymes. produced by the yeast cells, cause the sugar molecules in the liquid to split apart into alcohol and carbonic acid gas. The gas rises in bubbles to the surface; the alcohol remains in the brew.
 Yeast pr0toplasm contains all the life element found in animal proto- plasm, but in yeast the elements are so combined that they form four com pound substances: cellulose like wood fibre), protein (like white of egg), fatty matter and water. If a culture of yeast spores be dropped in "a basin of fermentable liquid, the comparatively few cells in the culture, multiplying in doubling numbers, will give birth to millions within a few hours, and each of those millions pro- duces it's enzymes. Since only plant cells are capable of producing cellu- cells
 Yeast is a very primitive plant, for 1t contains neither starch nor chloro- phyli (green coloring matter), so it is classed among the fungi.
 Dough contains sugar, and when the yeast enzymes split the. sugar molecules apart into alcohol and car bonic acid gas, the rising gas causes the bread to rise. There is always a trace of alcohol in bread.
 To exist, yeast cells must breat oxygen, the same as all other living organisms. But yeast does not de- pend entirely upon the air for its oxygen. If air be excluded from a vessel whereon fermentation is taking place, the multiplying cells suck oxygen out of the liquid: when this is exhausted they decompose molecules of the liquid and rob them of their oxygen atoms.
 Yeast spores float invisibly in the aid. Their exceeding smallness, the ease with which they are waited about by the winds, and their count less numbers everywhere in worm climates, explains why fermentable liquids cannot be kept fresh when exposed to the air.