Great care and skill are required in the mak ing of leavened bread. There is always danger that during the process of fermentation lactic acid and other products which are disagreeable to the taste will form along with the ea rbonk acid gas: then, if the leaven stands too long, it will reach the state of putrid fermentation.
With the of the yeast-plant (see YEAST), which was first applied to beer-making, the method of making fermented bread has been changed by substituting yeast for decomposing dough. The action of the yeast-plant—like that of leaven—when brought into contact with flour and water is to develop earbon dioxide and al cohol; the latter passes off in the oven in the form of vapor, the former is largely retained in the dough. The lightness of the bread depends upon the amount of this gas which remains im prisoned in the dough and distends it; hence it is due to the tenacity with which the grains of flour cling together, or, in other words, to the stickiness of the flour. It is in this respect that the superiority of wheat flour over that from all other grains lies. The sticky gluten of wheat does not allow the gas to escape. For this reason the quality of bread made from less tenacious flour is improved by mixing with it a portion of wheat flour.
'1'lle chemical .reactions concerned in bread making and the eonditions under which they are produced are easily understood. The process consists in adding to the flour and warm water the necessary amount of yeast. The yeast may be added directly or a preliminary ferment may be formed by mixing it with potatoes. if the latter method is employed, the yeast is put into a thin liquor, formed by mixing mashed potatoes with warm water. and the mixture is allowed to ferment for some time. The advantages claimed for the potato ferment are that "the yeast-cells arc strengthened by the soluble nitro genous matter of the potato. which acts as a yeast stimulant and enables a smaller quantity of yeast to hydrolyze a larger amount of starch. The yeast-cells then net very rapidly on the glu cose thus produced from the starch and develop the alcoholic fermentation." The proportion of water required to mix with the dough and yeast to form the 'sponge' depends upon the quality of the flour, as the gluten flours take much more water than the starchy flours, but enough should he added to make the sponge as moist as can be molded readily with the hands. The dough should be thoroughly kneaded, so the yeast will penetrate to every part of the mass. It should then be allowed to stand in a warm place. for
a proper temperature is an essential condition and the alcohol formed by the fermenting action is driven off. The carbon dioxide is also ex panded. By wetting the loaves before they are put into the oven, the crust is formed more rapidly, and the too rapid expansion of the dough is checked. Steam is sometimes injected into the oven while the bread is baking, thus glazing the crust and keeping the interior of the bread more »mist. Baked bread consists of two portions, the crumb and the crust, which differ frmn each other both physically and chemically. These dif ferences are due to the more sudden and intense beat to which the crust is subjected. The action of the heat and of the steam rapidly decomposes the starch into dextrin and maltose, which are caramelized by the heat, and so the surface takes on a brown color and a sweeter taste. The ac companying table shows the chemical difference between the crumb and crust of bread, according to the analyses of German and American investi gators.
That fermented bread is more healthful than unfermented is now generally admitted by physi cians. Being porous, it is easily masticated and more thoroughly aiirated during the process, so to the fermenting process. The most favorable temperature is from 70° to 75° F.; if it is al lowed to rise above 90° acetic. lactic, and pos sibly other organic acids are liable to form; in other words, the bread sours. If, on the other hand, the temperature is too low, the process of fermentation will not take place. The yeast begins to act upon some of the starch of the flour, changing it to sugar, and then decompos ing the sugar into carbon dioxide and alcohol. it is not until the second stage is reached, and the gas begins to form, that the action is visible. After the process has gone on for a time, until the whole mass is honeycombed, the dough should be subjected to a second thorough kneading. to break up the huge gas-bubbles into many small ones and distribute then; evenly through the mass of dough. The thoroughly kneaded mass is next molded into loaves and allowed again to `rise.' As bread loses a portion of its nutritive properties each time it is molded, the process should not he repeated too often. Bread which has been kneaded only once has a. sweeter flavor than that molded twice. but its texture is coarser and its appearance less attractive. The loss of nutritive value is from that portion of the starch which is converted into alcohol and gas.