The following experiment, made by Professor Jago, taken in connection with other recent experiments showing that foreign ferments in bread impair the food value, prove conclusively that it is far better to use plenty of good yeast, than a small amount, or poor yeast, or use no yeast, but simply a starter and depend upon spontaneous fermentation. In the experiment, sterilized vessels are used, and the same amount of wort placed in each. The vessels are loosely covered and the temperature is kept at 77 degrees F., - a temperature best adapted to allow the yeast to overcome the foreign ferments. One vessel of wort was left plain, that it might ferment spontaneously; to the second, fifteen grains of good brewer's yeast was added; to the third, ten grains of compressed yeast was added. The two with yeast were aerated; the other one was not. They were allowed to stand the same length of time, and on examination, the one to which no yeast was added was found to be swarming with bacteria, and no yeast cells were present. Those which were started with yeast had practically no foreign ferments. The conclusion drawn is that at that temperature yeast is vigorous and hardy, and overcomes the power of foreign ferments. Yeast always produces a sweeter and finer-flavored bread than other ferments do. Yeast which is made with hops is able to overcome the power of foreign ferments longer than that made without hops, because the bitter of the hops is not suited to bacterial growth, but since one can use but little of a yeast made with hops without injuring the flavor of the bread, and a weak yeast acts so slowly as to cause disastrous results, it is better to make yeast oftener without hops, and use plenty of it in bread making. There are a number of different kinds of yeast. Brewer's yeast, according to the best authority, is not the best yeast for bread-making purposes, because the brewer's business demands yeast, and he uses good yeast in his business, and the supply of best yeast is consequently limited. In a fermenting liquid, the middle yeast is considered stronger and more vigorous than that on either the top or bottom part of the fermenting liquid. Therefore it is wise for the breadmaker always to stir the yeast well before taking out a portion for breadmaking. In speaking of brewer's yeasts, Jago, in "Science and Art of Bread Making," says: "Too frequently that sold to bakers is the refuse yeast from either the beginning or the end of fermentation. Bakers who use brewer's yeast should insist on being supplied with that equal in quality to what the brewer himself uses in starting fermentation. To the baker, as regards yeast, above all things, the best is the cheapest. One spoiled batch of bread will cost the difference between good and bad yeast, over probably many weeks or months."
What is true of poor yeast in the bakery is true of poor yeast in the home. There are yeasts known as "patent yeasts." These are made by bakers for their own use. There is no reason why these yeasts should not be universally good, provided the baker is skilled in the art of manufacturing yeast, and is willing to give it sufficient attention, and to use only the best materials in its manufacture. The author quoted before says : "In making patent yeasts, it is very poor economy to stint either malt or hops. A weak wort produces a much less healthy and vigorous yeast than does a strong one, besides being much more subject to disease fermentation and consequent acidity." The same rule will apply to making yeast, at home. The yeast must be made often and the vessels must be sterilized, and a strong and vigorous yeast used to start with, if one would obtain the best results and avoid a weak yeast, with many foreign ferments.
There is another variety of patent yeast known as "flour barm." This is extensively used in Scotland. The chief peculiarity of bread from this is its decidedly acid taste, thought to be due principally to lactic acid. Much salt is used in making this bread, and it has not the flavor of what, in some other countries, is called the best bread.
*"Virgin barm differs from Parisian only in being self-fermented. Parisian barm was introduced from Paris to Scotland about thirty years ago. It is essentially a leavening ferment, a scientific modification of the systems of ancient Egypt and modern France." Dry Yeast.
The dry yeast cakes of commerce are simply yeast made by some one of the foregoing processes, and mixed with some cereal preparation, cut into cakes, and dried. Dry yeast, when it can be obtained fresh, will make a very good quality of bread. In making bread with this yeast, it is well to use potato water. In making yeast, it is necessary to have both carbohydrate and pro-teid matter. Such grains as corn, rye, and barley are used. A small amount of grain is best malted and then reduced to the proper fineness. It is then fermented to the proper stage, when the "starter" yeast is added, and it stands from ten to fourteen hours at a certain temperature. The other necessary grain is prepared and added at the proper time, and after a series of necessary manipulations, the yeast rises to the surface, is skimmed off, washed, properly prepared, and made into the cakes in which we see it. For a full description of the process of making compressed yeast, see "Science and Art of Bread Making," Jago.
Good compressed yeast should not be waxy, but should break brittle. It should have a pleasant odor, and act quickly when added to a sponge. Compressed yeast, when fresh, is strong and vigorous, certain to produce good results under proper conditions and handling. The only objection to this yeast is that it is expensive, and does not keeep fresh long. While we pay what seems like a large price for a small amount of yeast, we get more good lively yeast plants in one of those small cakes than in a much larger quantity of other yeasts. It is better to buy this to start with, when possible, for good wholesome bread can be made with home-made yeast if one has good yeast to start it with; but after home-made yeast is used several times to start with, the yeast produced becomes too weak for the best results, and needs reinvigorating. Home-made yeast is best kept in a glass jar. Such a receptable can be washed and sterilized each time fresh yeast is made, and this is absolutely necessary to insure the yeast against foreign ferments. Compressed yeast keeps best with the wrappers removed, and the yeast put into a glass jar and covered with cold water. The water should be changed the same as on cut flowers. The yeast must then be measured with a spoon when used.