Compressed yeast

Influence of the Degree of Hydrolysis of the Gluten on the Yield in Yeast. 

Catalysts which intervened in the hydrolysis. Estimate ol the dc sree of hydrolysis according to the formaldehyde nitrogen. Yeast yielded per 100 grams of fermented sugar. Nitrogen in the yeast harvested. 

The return in yeast increases as the hydrolysis is accentuated the gluten which was peptonized up to only 9 per cent of formaldehyde nitrogen furnishes 10.2 g. of yeast, containing in all 195 mg. of nitrogen. A thorou peptonization with pepsin leads to a yield of 16.2 g. of yeast, which has taken from the nutritive 

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Compressed yeast is also sold in supermarkets in 18-g and 56-g packages. Since this product contains approximately 10% added starch to increase its shelf life, it has a lower protein content and fermentative activity than the compressed yeast sold to bakeries. 

Active Dry Yeast (ADY). The production of active dry yeast is very similar to the production of compressed yeast. However, a different strain of yeast is used and the nitrogen content is reduced to 7% of soHds compared with 8—9% for compressed yeast. The press cake made with the active dry yeast strain is extmded through a perforated plate in the form of thin strands with a diameter of 2—3 mm and a length of 3—10 mm. The strands are dried on endless belts of steel mesh in drying chambers (a continuous process) or in roto-louvre dryers (a batch process), with the temperature kept below 40°C. Drying time in drying chambers is 3—4 h and in roto-louvre dryers is 6 h or more. The final moisture level attained is 7.5—8%. 

Instant Active Dry Yeast. Instant ADY (lADY or HADY) production is similar to ADY production but requires a different strain of yeast. After pressing, the yeast is extmded into noodles 0.2—0.5 mm in diameter and 1—2 cm long and deposited on a metal screen or perforated plate in a fluid-bed air dryer. Drying time is shorter than with ADY, about 1—2 hours in practice, with a final moisture level of 4—6%. Instant active dry yeast does not require separate rehydration. It is always packaged in a protective atmosphere or under vacuum. On an equivalent soHds basis, the activity of lADY is greater than that of regular ADY, but stiU less than that of compressed yeast. 

Active dry yeasts of improved quality have been available for many years, and more recently instant active dry yeast has been introduced (15,20). This instant yeast exhibits more activity than regular active dry yeast due to improved drying techniques, and can replace compressed yeast at a rate of 33 —40%. Dried yeasts, which are stable for long periods of time at room temperature, are of interest to bakers because of the high distribution cost of fresh compressed yeast. This is especially tme for those away from distribution centers and for smaller bakers whose usage rate of yeast is low. 

Forms of Yeast. Yeast is available in several forms compressed yeast, cream (effectively a liquid), dried into pellets and powders claimed to be instantly active. Bakeries normally use compressed yeast, which with cream yeast must be kept under refrigeration. A supply of dried yeast will always be kept handy lest the yeast delivery should fail or the refrigerator breaks down. 

Dried Yeasts. The traditional form of dried yeast is known as active dry yeast (ADY). This product normally only had 75-80% of the gassing ability of a compressed yeast on an equivalent basis. ADY has to be rehydrated with water at around blood heat before it can be used. 

High Sugar Yeasts. These are products specially produced to work under the high osmotic pressures in products like Danish pastries. These yeasts are available in the form of IADY products. There are also some Japanese strains of compressed yeast that can stand high osmotic pressures. 

One day while I was examing a suspension of yeast freshly prepared from a few bits of compressed yeast shaken vigorously with a little water in a test-tube, I failed to find the characteristic four-banded absorption spectrum, but before I had time to remove the suspension from the field of vision of the microspectroscope the four absorption bands suddenly reappeared. This experiment was repeated time after time and always with the same result the absorption bands disappeared on shaking the suspension with air and reappeared within a few seconds on standing. 

Compressed yeast (Cerevisiae Fermentum Compressum) N. F. consists of the moist, living cells of Saccharomyces cerevisicB or of other species of Saccharomyces, combined with a starchy or absorbent base. 

Rye is very largely used in distilleries which produce potable spirit such as whiskey, gin and vodka, and in the manufacture of compressed yeast. It is also used in relatively small amounts in the yeast mashes of alcohol distilleries. It is not suited to use as the chief ingredient of the mash in an alcohol distillery, on account of the tenacious quality of the mash which it forms. Furthermore, it gives a low yield in proportion to the amount of starch which it contains. Though it usually contains over 60... 

Bakers use either compressed yeast (compressed cakes of top yeast) or dried yeast (a mixture of yeast cells with starch). The former has high fermenting capacity and gives uniform results, but it will keep only a day or two while the latter retains its capacity to produce fermentation for a long period. Brewers yeast is not desirable for bread making because it is likely to give a bitter flavor and its activity is slow in a dough mixture. 

Pure Cultures.—To determine the properties due to a particular yeast, it must be separated from all other organisms with which it is associated and when grown thus, free from all contamination, it is then known as a pure culture. A commercially pure yeast is different, as this simply means free from added non-yeast matter. This is the condition of most compressed yeasts as found on the market they are commercially, but not bacteriologically, pure, since they have numbers of bacteria and molds associated usually with more than one yeast variety. 

If compressed yeast iB used 1 pound wifi be sufficient to start a 20-gallon mash, and if culture yeast from a laboratory is used 1 gallon (which is the amount usually sold) will start a 10-gallon mash. 

There are three different preparations of yeast for bakers, on the market compressed yeast, dry yeast, and liquid yeast. Compressed yeast is mads from distillers wort. After the yeast has been collected from the wort, it is thoroughly washed, and then passed through wire and silk sieves to free it from foreign materials. After this cleaning process the yeast is pressed, cut into cakes, and wrapped in tin foil. Compressed yeast cakes are liable to start decomposition unless kept in a cool place. 

Dry yeast is prepared by taking fresh liquid yeast and mixing it with com meal, flour, or other starchy materials. This mixture is dried at carefully regulated temperatures. If the dry yeast is made properly it will keep for a long tuna However, the percentage of living cells in dry yeast slowly decreases and it must be remembered that the number at the start is less than in the case of compressed yeast. 

Schutzenberger and other European workers have demonstrated the toxic action of wheat flour on brewers yeasts, but state that the bakers compressed yeast is immune to the toxicity of wheat flour. I find, however, from the experiments performed that the bakers compressed yeast is not entirely immune from tire toxicity of wheat flour, though the action is far more pronounced on brewers yeast. 

At the end of the fermentation the yeast is separated from, the wort by use of centrifugal machines. In producing compressed yeast of about 75% moisture from separator yeast, square iron filter presses are used., Finally. the yeast is passed through cake cutting and wrapping machines. The ope pound package is largely used by commercial bakeries while the small cakes are sold for use in the home. 

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