Mix some flour into a dough and bake it. The result will be a coarse, tough, indigestible cracker.

The flour and water product possesses keeping qualities, but can only be used as a food when soaked in a fluid.

A baked product if used as a nutriment must possess lightness and porosity and be so constituted that it can be easily digested.

For this reason yeast is required in bread making.

Yeast.

A Gas Test.—Dissolve in a flask 2 ounces of syrup or honey in a pint of water at 140 degrees F., and add one-sixth of an ounce of compressed yeast, which has been broken up and dissolved in a part of the saccharine infusion. Seal the flask with a perforated rubber cork, pass a bent glass tube through the perforation and attach a piece of rubber hose to the glass tubing. In fifteen or twenty minutes small bubbles will be seen rising to the surface of the fluid, which will continually increase in number, until the surface is covered with a froth formation, somewhat like the head of a cauliflower.

The fluid is fermenting.—After 1 to 1½ hours the froth forming gradually ceases and finally drops.

During fermentation lead the rubber hose attached to the generating flask into a smaller flask half filled with water. You will notice bubbles oozing from the mouth of the hose through the water. Then at once make a test by holding a lighted match into the small flask. The match will burn readily, just as it would in the air. After ten or fifteen minutes repeat this procedure and the burning match will be extinguished at once, even to the glimmer.

During the first test atmospheric air only was contained in the small flask. It required a little time for the gas of the generating flask to displace the atmospheric air, as a result of which the lighted match went out at the second test.

Another peculiar phenomenon is noticeable in connection with this test. On top of the water in the open flask the developed gas remains stationary, but can be dispersed by an air current, either created by blowing or by waving the hand over the opening of the bottle.

If we then pour some clear lime water into another small bottle and allow some of the gas from the generating flask by means of the rubber tubing to flow into the same, we will find that, after withdrawing the hose, closing the bottle with the thumb and slightly shaking the contents, the lime water turns milky.

This is caused by a combination of the dissolved lime and the gas. The latter, which we have developed, is Carbon Dioxide (CO₂).

By the above tests we find that Carbon Dioxide is heavier than the atmosphere, and thus remains in the bottle undisturbed by atmospheric pressure, for a time, as it combines very slowly with the air. By creating a draught, the combining with the air is facilitated.

Top and Bottom Yeast.

Remove with a glass rod, during active fermentation, a little of the froth from the saccharine infusion and wash it off with a few drops of clean water, and place a small drop of the solution upon the object glass of the microscope. At 300 to 500 magnified strength we notice that the froth consists of small round or oval bubbles, which occasionally, though seldom, are elongated. They appear singly or in groups, and often look like strings of pearls. These bubbles are yeast cells. Figure 5 shows yeast cells after five hours of propagation. Each cell has a thin covering of fibrin or cellulose; while the interior contains a soft granular albuminous substance, called Plasma, or Protoplasma.

During vigorous fermentation at a temperature of 68 to 80 degrees F., the majority of the bubbles are forced to the surface of the fluid by the action of the escaping Carbon Dioxide, and at the final stages of fermentation gradually precipitate. At a temperature of 36 to 45 degrees F. the fermentation is slower, the generating Carbon Dioxide is less active in escaping and without sufficient force to bring the bubbles to the surface. The yeast cells to a great extent grow and settle on the bottom of the generating vessel.

These characteristics designate top and bottom yeast.

Both of these yeasts are of the same species, and either can be converted into the other by the changing of the temperature during propagation. They are recognizable by a slight difference in size. Owing to the more favorable conditions during growth top yeast is somewhat better developed than bottom yeast. Compressed yeast used in bread baking is top yeast.

Distillation Test.—After the fermentation in the generating flask has ceased, and no more bubbles rise to the surface of the fluid, test it by distillation. For this purpose we first filter the saccharine fluid to remove the yeast cells. Place the clear filtrate in a clean flask, stop it with a perforated rubber cork, and connect it by means of a bent glass tube with a cooling apparatus. Figure 6 shows such an apparatus. The vapor generated from the filtrate contained in the flask passes through the coil in the cooler, as shown in the illustration. The cooler is provided with tube connections at the lower and upper ends, which can be fitted with perforated corks, through which glass tubes may be inserted.

The lower tube by means of rubber tubes is connected with the cold water faucet, not shown in the illustration; the flow of cold water around the coil can be regulated at the faucet and drawn off at the upper tube.

In lieu of a cooler as shown, one can be constructed by leading the tube of the filtrate flask into a somewhat wider and longer glass tube, which is connected with a second bottle. The long glass tube, in this case, must be kept cool by constantly pouring cold water over it during distillation.

When all connections have been made tight, heat the filtrate over an alcohol lamp to a boiling point, the flask having been placed on a piece of wire gauze to equalize the heat. The arising vapors passing through the coil are condensed, and drip like tears into a receptacle placed underneath the cooler. This evaporating and condensing of a fluid is called distillation.

The portion of the condensed fluid coming over at the beginning will be found, if tasted, to be very strong spirits of alcohol. Light it with a taper, it will produce a large bluish flame.

As the distillation continues the spirits coming over lose gradually in strength until finally very little else but the vapors of water are condensed. Water boils at 212 degrees F., spirits of alcohol at 172 degrees F. We would therefore infer that at the beginning of distillation it is possible to recover alcohol only if the infusion was heated to 176 degrees F.

This view, however, is erroneous. The boiling point of the mixture is only slightly greater than that of pure alcohol, and the generated vapors are already at the beginning and combination of both fluids, although at first the proportion of alcohol is the greater.

We have now seen that yeast is capable of producing alcohol and carbon dioxide. This is called alcoholic fermentation.

Wine, beer, brandy and other spirituous liquors are produced by alcoholic fermentation, and the same is attributed to the raising of bread doughs.

The yeast cell in its search for nutriment consumes and changes the sugar, to facilitate growth, finally reducing it into simpler bodies of alcohol and carbon dioxide.

The chemical changes of the sugar are due to the ever-changing composition of the albuminous plasma of the yeast cell. When the plasma has lost the power to renew itself, it dies and putrefaction sets in.

Worts of sugar and diffusible albuminous solutions are ideal foods for yeast, as they readily permeate the fine, porous coverings of the yeast cells to nourish the plasma, which at the same time, by its own action, creates the requisite warmth by the dissolution of the sugars with alcohol—carbon dioxide.

The following description will illustrate how this is accomplished:

Make a drumhead, by stretching and fastening a piece of bullock’s bladder or either vegetable or animal parchment paper over a cylinder of glass. Place this in a vessel containing pure water, and pour into the cylinder a strong solution of common salt. The salt brine and the pure water are only separated from each other by the thin membrane of the bladder or the parchment. After a little while it will be noticed that the salt solution will have diffused out through the membrane until the liquid, both outside and inside the floating cylinder, has the same strength. This is called osmose, or dialysis.

In choosing its nutriment yeast is very selective. Of the carbohydrates, glucose, maltose and those of C₆H₁₂O₆ group are capable of direct fermentation, and are quickly and vigorously changed by yeast. In direct opposition, we find that cane sugar, beet sugar, as well as the starch of flour, are not fermentable until chemically changed. This change is brought about by yeast itself.

The plasma of the yeast contains an albuminous substance called Invertin. As explained above, the Invertin, by dialysis, is diffused out through the cell covering and changes cane sugar and sugars of the same class, as well as part of the flour starch, into fermentable sugar, known as invert sugars.

Reproduction of Yeast.—During fermentation yeast nourishes and reproduces itself. The granulations of the living plasma divides itself, and with a portion of the plasma forms a small protuberance at one end of the cell; it then enters the neck, which is gradually developed by the contraction of the cell wall and forms a bud.

The neck finally closes, the budding daughter cell releases itself from the parent cell, and each are then an individual organism.

This operation is known as “budding.” Each parent cell is capable of giving off several buds in succession. The daughter cells in their turn reproduce in the same manner, and so with remarkable rapidity yeast cells multiply.

But yeast is also reproduced by spores termed “ascospores.”

In this case yeast cells do not throw out a bud, but the plasma divides itself into (usually) four portions called spores, each of which surrounds itself with a thin membrane.

These spores, when set free by the dissolution of the cellulose coverings of the parent cells, on account of their minuteness float away into the atmosphere. If by chance they drop into the proper medium, such as malt wort or flour barms, spontaneous fermentation sets in.

This is recognized by the fact of spontaneous fermentation frequently and easily occurring in the fermenting rooms of yeast factories and breweries, as innumerable quantities of spores are present in the atmosphere at all times.

Pure Yeast Cultures.—By the manner in which yeast nourishes and reproduces itself, we acknowledge it to be a plant of exceedingly elemental structure.

Being devoid of the green coloring matter of the plant (chlorophyll), the yeast cell is incapable of assimilating inorganic matter, such as carbon, nitrogen, ammonia and certain mineral salts, for the purpose of building up their tissues.

Yeast belongs to the family of Fungi, and on account of the peculiar manner of its reproduction is classified as “Sprouting Fungi.”

We are obliged to admit that the true nature of the yeast cell has as yet never been entirely satisfactorily explained. Some scientists are of the opinion that yeast cells are but the embryo of higher fungi development; for it is known as a fact that certain species of the sprouting fungi do not possess the faculty to incite alcoholic fermentation, while, on the other hand, some of the higher species of mould fungi possess the qualification not alone to incite alcoholic fermentation, but are also capable of ascospore formation. So much for this explanation.

It has been proven by actual results that different species of yeast produce widely different kinds of fermented liquid. These differences are recognized in the yeast cell of wine, of beer, and of the distillery, the last named being also the yeast of dough fermentation.

If the yeast cell of wine be placed in a beer wort, the fermented wort will assume a vinous flavor, and is known as maltine.

Science has shown that yeast cells are composed of groups of various species. The principal species, among others, as found in brewers’ or distillers’ yeasts, are known as Sacchoromyces Cerevisial and Sacchoromyces Pastorianus.

Both are very much alike in appearance, both incite alcoholic fermentation, but develop in a similar wort a number of widely different by-products, the analyses of which have thus far baffled the resources of the chemist. The action of these two species is readily recognized by the flavor and taste imparted to the fermented medium.

As the bouquet imparted to wine is attributed to the wine yeast cell (Sacchoromyces Ellipsoideus), characteristic of the grape juice, so the baker recognizes by the flavor of his baked product that the proper species of yeast has been employed, irrespective of the flavor which may have been obtained by other materials used in the baking.

While it is difficult to separate the various species of yeast cells, the phenomena of spore formation has led the way to accomplish it.

At a temperature of 54 degrees F., Sacchoromyces Cerevisial will show ascospore formation in 200 hours, while Sacchoromyces Pastorianus at the same temperature forms spores already in 77 hours. This difference in time of the maturing of the spore formation of the various species of yeast being known, is utilized in transferring the spore of any specific species upon culture plates of nutrient gelatine, upon which the spores develop into little colonies of yeast cells.

The healthiest and strongest appearing cell is then cut out with a sterilized platinum wire and transferred into a flask of sterilized malt wort, and the reproduction from a single cell of any given species is begun. In this manner pure yeast culture is accomplished.

In the fermenting vats growing yeasts are often contaminated by spores of undesirable species from the atmosphere, and result in producing conditions unfavorable for the purposes desired. In such cases we must resort to a pure yeast culture to re-establish the desired fermentation.

Manufacture of Compressed Yeast.—Compressed yeast is the result of alcoholic fermentation of malt and grain worts. As it is of material interest to the baker to acquaint himself with a general knowledge regarding the manufacture of compressed yeast, a short but clear description is given below.

Treating the Grain.—Malt is produced by soaking barley or other grains in water and spreading in thin layers on the floors of the malting rooms. Being moist and in consequence supplied with artificial heat, the grains begin to sprout. As the rootlets grow in size a product is being formed in the germ that has the power to convert starch into sugar. This product is called Diastase. This reaction is still clouded with a good deal of mystery, and it has as yet never been clearly defined.

We know this much, however, that some parts of the nitrogenous matter of grains are chemically changed into Diastase.

Practice teaches the maltster, by the size the rootlets attain, when the maximum diastasic strength of the malt has been reached.

The sprouting of the malt is now arrested by drying the malt in kilns at a temperature of 131 to 176 degrees F., which evaporates the moisture and kills further germination.

For malting purposes barley is mostly used, as its diastasic strength exceeds that of any other grain.

The Yeast Mash.—For preparing the yeast mash crushed malt and rye is employed, although other grains are used to replace part of the rye, such as corn and buckwheat.

Experience teaches, however, that the best results are obtained by the use of barley malt and rye only.

The materials are selected with great care. The water employed is boiled, the rye must be clean and free from dust, and the malt free from mould. The rye is first soaked in water and then crushed.

In 200 liters of water at 125 degrees F., 100 kg. of the grains are mixed and constantly stirred for thirty minutes, until all lumps have disappeared, the temperature in the meantime remaining constant. At this temperature the dissolving of the albuminous matters of the grains is favored, and the changing of the starches into sugar and dextrin is facilitated.

Saccharification of the Mash.—At the expiration of the thirty minutes the temperature of the mash is gradually increased by steam from 122 to 158 degrees F., and constantly stirred.

It has been substantiated that these temperatures are best suited for a perfect gelatinization and saccharification of the starches without injuring the diastasic properties of the malt. At the same time, a temperature of 158 degrees F., which is continued for two hours, is useful to effectually sterilize the mash by destroying the undesirable bacteria. During this time the diastase, which, as we have seen, was produced in the sprouting barley during malting, effects its function in the quickest possible manner. The result is a very sweet, lasting fluid.

In order to ascertain whether the saccharification has been complete, a small portion of the mash is filtered and tested with a drop of tincture of iodine. When the tincture of iodine discontinues to produce a blue coloring in the filtered fluid the saccharification is complete.

Acidulation of the Mash.—This is probably the most momentous stage of compressed yeast manufacturing, and watchfulness must be practiced, if the object be to produce a pure yeast free from all possible contamination.

The means used for this purpose is the introduction of lactic acid fermentation. The mash is covered up, occasionally the mash is stirred, but always from bottom upward, so as to bring as large a surface as possible in contact with the atmosphere (oxygen), while the mash is kept at a temperature favorable to lactic ferment growth.

The reason for this acidulation is twofold. In the first place, the lactic ferments assist in converting the insoluble albuminous matters of the grains into soluble matter. Technically, this is known as changing the albuminoids into peptones.

In the second place, lactic ferment is absolute poison for the undesirable bacteria, which may have developed, without injuring in any way the yeast cells proper, but rather has an influence for good toward them. Sulphuric acid is sometimes added to increase the acidity.

When the acidity reaches 2½ per cent. in the mash it is ready for further manipulation. Apparatuses to indicate the per cent. of acidity developed are used for the purpose of accuracy.

The acidulation of the mash having been satisfactorily completed, further operations are dependent upon the method selected to produce yeast. The older method is known as the “Vienna Process,” while the newer method is called “Aeration Process.”

The Older or Vienna Process.

Fermentation of the Mash.—At the completion of the acidulation of the mash it is at once cooled to 77 degrees F. This is accomplished by continuously agitating the mash by mechanical means with hollow plungers that are filled with ice or cold water, and which at the same time serves to aerate the mash.

The former method of cooling the mash in shallow vats, on account of infection and introduction by and of undesirable bacteria from the atmosphere into the mash, has been generally discarded.

Fermentation is now introduced by adding a certain quantity of compressed yeast, which must be free from starch adulteration.

In a short time a head begins to develop upon the surface of the mash, which gradually grows and rises to the top of the half-filled vats. The period of fermentation depends upon the temperature of the mash as well as the density of the mash.

The higher the density of the mash, the more vigorous the fermentation.

In general, the time consumed for proper fermentation is twelve to eighteen hours.

As fermentation proceeds, the density of the mash becomes less, while the yeast cells increase, and at the same time the temperature of the mash raises.

The mash in this process contains the whole of the grains, and for this reason the head, which contains the yeast cells, and which is skimmed off as it rises, must be strained; it is subsequently washed and then pressed. In contrast to this method the newer or “Aeration Process” for the production of yeast presents entirely different phases.

Production of Yeast by Aeration Process.

This method was invented in Sweden about ten years ago, and is in use in many yeast factories to-day. A decided greater percentage of yeast yield is accomplished by the “Aeration Process.”

After the saccharification of the mash is completed, the extract called “wort” is strained to remove the husks and bran of the grains. Large vats containing a double bottom are used for this purpose, the inner or upper bottom being perforated. Spigots are attached to the bottom of the vats to draw off the “wort.” At first the extract appears opaque and is again returned to the mash. This pouring-back process is continued until the “wort” finally flows perfectly clear from the spigots. The extractive matter still adhering to the husks and bran of the grains is washed out or “sparged” with hot water.

Another way employed for recovering the clear “wort” is by means of the filter press. The percolation method, however, is preferable, as the extraction of the essential properties is more complete.

Fermentation is produced in the “wort” by adding small quantities of compressed yeast also, or by the use of pitching yeast. During the fermenting period a continuous stream of atmospheric air is forced through the “wort” by the aid of air pumps. In order to eliminate atmospheric dust and bacteria, the air before entering the “wort” filtered through cotton, and sterilized by passing it through a solution of salicylic acid. It is also necessary to distribute the air to all parts of the “wort” equally, by means of perfected tubes, which are attached to the main air pipe, branching out in various directions at the bottom of the fermenting vats, with the perforations facing downward. At the beginning the air current is very moderate, and is increased in accordance and in proportion of the yeast growth. At the final stages of fermentation the air current is again moderated. This forcing in of air, or rather oxygen, in the “wort” stimulates in an exceedingly large measure the propagation of yeast, but care is exercised in this respect, however, for if the air pressure be too strong a large per cent. of alcohol, a very important by-product, will be lost. The characteristic feature of this method, distinguishing it from the Vienna Process, is the continued aeration during fermentation, hence called “Aeration Process.”

Obtaining the Yeast.—Fermentation of the “mash” or the “worts” proceeds at a lively rate. In observing the “head” or froth, during the “Vienna Process,” which at first is transparent, gradually assumes a milky or of more opaque appearance, caused by enormous increasing growth of yeast cells, filling up the froth bubbles. When the cells are fully developed the fermentation may be considered finished. Practice assumes, although the assumption is not always reliable, that this stage has been reached when the “head” or froth begins to recede. The only sure method to determine proper maturity of the yeast cell is by microscopic observation.

Placing some of the froth under the object glass of the microscope, the yeast cells most appear well developed and isolated from each other. It should be the exception rather than the rule that budding cells still be visible.

Not until assured that the proper time has been reached should the skimming of the upper portion of the froth be begun. This portion of the “head” contains the so-called “pitching yeast,” and is used largely in starting new propagation.

Large galvanized perforated spoons with long handles are used to skim off the froth. Repeated observations of the froth during the skimming are made, to ascertain the condition of the yeast cells.

The yeasty froth is immediately mixed with ice cold water to arrest further fermentation. This also serves to increase the keeping properties of the yeast.

The water containing the skimmed-off matter is now run through strainers of varying sized meshes, the coarser retaining the husks and bran, while the finer meshes prevent the gummy matter adhering to the yeast cells from passing.

The strained yeast cells are caught up in vessels containing water, where they precipitate in a compact layer, and is then ready to be washed.

In order to watch the settling of the yeast, these vessels are constructed with windows so as to give the operator a perfect vision of the settling.

This operation of washing the yeast in new water and allowing it to settle is repeated several times, at which time nearly all of the impurities have been removed and excellent keeping properties have been attained.

A newer method of washing yeast has lately been introduced by the invention of a specially constructed patented centerfuge. If it be intended to mix starch with the yeast, it is usually done just after the washing has been completed.

Potato or rice starch are used. The utmost carefulness must be observed in the examination of the starches, as they frequently are contaminated with bacteria or acids, which tend to injure the keeping qualities of the yeast and very soon become unfit for use.

After the clear water of the last washing has been removed by decantation, the compact settled mass is pressed dry by hydraulic or filter press, and finally formed by specially constructed machines into pound pieces, familiar to all bakers.

The “mash” or the “wort” after the yeast has been removed contain alcohol in paying quantities, and is recovered by distillation.

One hundred kilograms of mash yields an average of 11 per cent. yeast and 28 per cent. of alcohol, if fermented according to the “Vienna Process.” The “Aeration Process” yields 25 per cent. of yeast and 18 per cent. of alcohol. The remaining grains in the liquids are much sought after for their value as desirable fodder for cattle.

Yeast Adulteration.—High class compressed yeast should be free from all adulterants. Most manufacturers, on account of the slimy matter of yeast, causing many difficulties in pressing, add from 5 to 10 per cent. of potato starch, claiming that it increases the keeping qualities by absorbing part of the moisture. The writer, however, does not agree with them.

Starch is undoubtedly at times added to yeast in large excess; it then becomes an adulteration; this fraud is, however, readily detected by treating the sample of yeast with iodine. For this purpose break up a little of the yeast in a test tube with some water, shake it up well and add a few drops of tincture of iodine; after standing a little while the starch will settle at the bottom of the tube in a dark blue layer.

Plaster of paris has also been found in yeast; this, besides being fraudulent, is decidedly criminal, and verily, is giving a “stone for bread.”

Nature of and Examination of Compressed Yeast.—A good sample of compressed yeast should have a creamy white color. A brownish discoloration would indicate that fermentation had been too far prolonged before skimming. It should have an odor of apples, not cheesy; neither should it have an acid odor or taste. A piece of blue litmus paper pressed against the cut of the yeast should remain neutral or at the most show but a faint sign of red; a marked change in the paper from blue to red would indicate acidity.

A microscopic view of good yeast dissolved in water should have the appearance as seen in Fig. 2, shown above. When broken it should show a fine fracture, irregularly rounded. Should it be crumbly, deterioration has set in. In lukewarm water it should melt readily, and not be sloppy to the touch. The dissolved yeast placed in a glass tube should settle slowly and evenly with the water above it perfectly clear. During this test adulteration with plaster of paris is readily detected, as it would be the first to settle out, and by carefully decanting the fluid, examination of the sediment would disclose plaster of paris.

If the solution of yeast and water does not clear itself the yeast is spoiled, and is of no use for the fermenting of doughs. It is contaminated with wild yeast and harmful bacteria, and would be instrumental in starting putrefactive fermentation, ruining the flavor of baked goods. Should we desire to ascertain the amount of starch present in an adulterated yeast, the following method is applicable:

Weigh a small beaker and a small glass rod on a very accurate scale; or, better still, on an analytical balance, and assume the weight to be 17.5 g. In the beaker place 10 g. of the compressed yeast under examination; break it up fine with the glass rod, and place the beaker in a hot water bath for several hours, weighing occasionally until two consecutive weighings are exactly equal; for instance, 21.2 g. We deduct from this the weight of the beaker and glass rod, giving us the following figures: 21.2 g. - 17.5 = 3.7 g.

The quantity of moisture evaporated out of the yeast would therefore be 10 g. - 3.7 = 6.3 g. According to the findings of Hayduck, pressed yeast contains originally 73.5 per cent. and dry starch 36 per cent. of moisture.

We now proceed to make deductions to determine the quantity of starch contained as an adulterant in the mixture. We set the example: “What per cent. of starch is contained in a mixture of yeast and starch if 10 g. of the mixture gives off by evaporation 6.3 g. of moisture, yeast containing 75.3 per cent. and starch 36 per cent. of moisture?”

Solution.—One hundred g. of pure press yeast, heated to dryness, gives off 73.5 g.; therefore, 10 g. heated should give off 7.35 per cent. moisture.

In our test the loss is but 6.3 g., consequently a deficiency of 1.04 g. This in itself indicates starch adulteration.

Starch gives off 36 per cent. of moisture; therefore, 1 g. gives off 0.36 g., and 1 g. of yeast 0.735 g. of moisture. With each 1 g. of starch addition the moisture loss is found to be 0.735 - 0.36 = 0.375 g. deficient.

In the 10 g. mixture under examination there is contained as many times 1 g. of starch as 0.375 g. is contained in 1.05 g., which is equal to 2.8 g. In a 100 g. mixture the result would be 28 g., or 28 per cent., which is the per cent. of starch adulteration in our mixture examined.

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.