The Fermenting Strength of Yeast
The best manner for the baker to test the strength of yeast is to take equal parts of the samples of the various yeasts, about 10 g.; dissolve in 100 g. of water at 85 degrees F., and make a dough with equal amounts of the same bread flour (about 1990 g.).
In order to prevent transferring of any one yeast sample to either of the other doughs, it is advisable to thoroughly wash the hands between each mixing. Place the doughs in glass jars of equal dimensions, and allow them to raise at an even temperature. It goes without saying that all ingredients must be weighed exactly alike, and the temperatures in all cases be the same. The yeast which gives the greatest expansion of the dough has the preference.
Another simple manner to test the strength of yeast is to drop a piece of the dough into tepid water (85 degrees F.), and observe the time consumed between immersion and when the piece of dough rises to the surface of the water. The dough which rises in the shortest time contains the strongest yeast.
Of course, in technical schools yeast strength is determined along different lines. A Hayduck carbonic acid measuring apparatus is used for this purpose, and is shown in cut (Fig. 9). It consists of two connecting glass tubes fastened against a board. The wider of the tubes has a capacity of 500 cc., and ends at the top in a narrow glass tube, to which rubber tubing may be attached, and is graduated in cubic centimetres. The other narrow tube ends at top funnel-shaped.
Through the funnel the apparatus is filled with water, colored blue to make observations easily. In order that the water may not absorb any of the carbonic acid gas, which would tend to make the test inaccurate, on top of the water in the wider tube a thin layer of petroleum is poured.
In gas generating flasks (A) a suitable “wort” and a definite amount of yeast, to be tested, is dissolved and placed in a water bath. (B) is a second flask for the next following test. (C) is a pinch-cock, which is left open so long as (D) is kept closed. The generated carbonic acid gas forces the water out of the wide tube and is caught up at (G). The yeast which has the ability to displace the largest amount of water at stated periods is considered the best fermentation inciter. Before any readings are taken the water in both tubes is brought to the same level by means of cock (E).
If care be taken to use the exact proportions of materials in each test at even temperature, reliable conclusions are obtained from each individual yeast sample.
Water.—Next to flour, water is the most abundant compound used by the baker. It is the great solvent of Nature. Pure water is composed of the two gases, hydrogen and oxygen, in proportions of 1 to 8. It is colorless and tasteless.
Water as found in nature is never pure. Owing to its action as a solvent, it contains bodies like lime, magnesia and potash in solution, besides air, carbon dioxide and other mineral matters. Hard water is such as contains more than seven grains of mineral salts per gallon.
The hardness due to bicarbonate of lime may be neutralized by boiling. Other mineral salts are penniment.
In general, soft water is more adaptable for bakers’ use, as hard water retards fermentation and somewhat checks the softening changes going on in the dough during fermentation.
Doughs made with hard water require to lay longer to properly mature.
It is for this reason that the baker will find it necessary at equal dough temperatures to modify his methods when using hard or soft waters to get uniform results.
It is of the utmost importance that water used in the bakery be free from organic matter that is detrimental to health, as many such organisms have a tendency to set up putrefactive fermentation in doughs.
In a broad sense, however, water that is declared fit for drinking purposes can be safely employed in bread work.
Salt.—Chemically known as chloride of sodium. It is produced from three different sources: Bay or sea salt, rock or mine salt, and natural brine or pit salt. Of these the refined product of natural brine or pit salt is to be preferred by bakers.
It should be dry, to insure uniform results, as wet salt contains a large percentage of water, which interferes with obtaining accurate and uniform quantities needed in the doughs.
It is added to doughs in varying amounts, from 1½ to 4 pounds per barrel of flour, and gives bread flavor and taste. When working with soft water more salt is required than in hard water. While salt gives the bread flavor, it also retards fermentation. It is especially of import by keeping in check lactic and butyric fermentation, causing sour bread. Authorities claim that salt in all proportions from 1.4 per cent. upwards retards fermentation and diminishes the speed of gas evolution, the raising of the dough.
Milk.—Is largely used in bread making. Dry milk on account of its convenience, has supplanted fluid milk in a large measure in the bakery.
Although not universally accepted, the writer is of the opinion that dry milk containing pure butter fat will add equal flavor to bread in which fluid milk is used.
Besides giving flavor and nourishing properties to bread, on account of its dryness it has water absorptive qualities that are of economic value to the baker.
Dry milk also contains soluble extracts that have an invigorating influence on yeast growth, i. e., fermentation, and improves and gives a better bloom in the crust of the bread.
In point of economic value, the baker should determine, by making small trial doughs, the increased volume obtained by reason of the extra moisture absorbing properties of dry milk when used in doughs.
Fat.—Lard, compound lard and cotton-seed oil are the fats generally employed in bread making. The use of fats effects a finer texture in the bread.
A colorless shortening assists in producing a whiter crumb, and also by coating the cells of the loaf retains the moisture of the baked bread. Doughs containing large amounts of shortening, under best and equal conditions, will stand a larger amount of proof, as part of the shortening in a well mixed dough has combined with the gluten of the flour used, allowing it to stretch further and become more elastic and still hold the increased amount of gas generated by the heat of the oven, and produces a loaf of greater volume.
Not all shortenings will produce the same effect, and the baker should experiment with small batches. The points to be determined are the effect the shortening has on the crust, volume of the loaf, as well as the color.
Sugar.—Among the sugar groups used in the bakery we find cane sugar, malt extracts, glucose and yeast foods.
Each of these products have characteristic effects on fermentation and doughs, and will be treated in a later paper.