Yeast, Dried

Active alkali Active chlorine Active dry yeast Active dry yeasts Active oxygen (AO)... 

Type B Torula Dried Yeast, Lake States Yeast, Rinelander, Wis., 1986. 

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. 

The dry yeasts have excellent storage stabiUty, up to a year or more if packaged under an inert atmosphere (N2, CO2, or vacuum). First introduced into the United States and then AustraUa, they are now being introduced into European winemaking as well. A number of strains of S. cerevisiae S. bayanus and S. fermentati are available. 

Spontaneous fermentations are used for wine production in Erance, some other European countries and in South America. In recent years, smaller California wineries have begun experimentation with spontaneous fermentations as well. They generally start more slowly than fermentations inoculated with commercial dried yeast, are more difficult to control, and may suffer from growth of undesirable contaminants. However, it is claimed that the resulting wines possess better organoleptic properties, particularly more complex flavor and aroma. 

Brewers and bakers dried yeasts are used as dietary supplements. They contribute some protein and trace minerals, and some B vitamins, but no vitamin C, vitamin B 2 or fat-soluble vitamins. The glucose tolerance factor (GTE) of yeast, chromium nicotinate, mediates the effect of insulin. It seems to be important for older persons who caimot synthesize GTE from inorganic dietary chromium. The ceU wall fraction of bakers yeast reduces cholesterol levels in rats fed a hypercholesteremic diet. 

Bakers inactive dry yeast is also widely used in the food industry. This yeast may be grown specifically as a food supplement and consequently there is a choice in its composition by varying growth conditions and feedstock makeup. It can possibly produce high levels of nicotinic acid and thiamin, the cmde protein content can be raised to 50—55% and it can be used as a vehicle for the incorporation of micronutrients such as selenium or chromium into the diet. 

Uses. Inactive dried yeasts are used as iagredients ia many formulated foods baby foods, soups, gravies, and meat extenders as carriers of spice and smoke flavors and ia baked goods. Yeasts used ia the health food iadustry are geaeraHy fortified with minerals and contain higher concentrations of the B vitamins, especially thiamin, riboflavin, and niacia (see Vitamins). 

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. 

Two 300 ml Erlenmeyer flasks are prepared, each of them containing 60 ml of the following vegetative medium in tap water 0.6% peptone, 0.3% dry yeast and 0.05% calcium nitrate. The pH after sterilization by heating in an autoclave to 120°C for 20 minutes is 7.2. 

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. 

More modern forms of dried yeast are now available, known as instant active dried yeast (IADY) and protected active dried yeast (PADY). These types of yeast can be mixed directly into dry ingredients, making them more effective at gas production than ADY. 

Because the activity of dried yeast is reduced by exposure to oxygen, IADY is supplied vacuum packed or with an inert gas in the head space. PADY, which has the yeast encapsulated in fat, relies on an anti-oxidant for stability. PADY is essential for domestic bread machines. 

Fresh yeast is definitely best but if it is not available dried yeast will have to be used according to the supplier s instructions. 

A 2 L three-necked round-bottomed flask equipped with a bubbler and a thermometer was charged with tap water (400 mL), sucrose (75 g) and dried yeast (10 g), added in this order. The mixture was stirred very gently (150 r.p.m.). 

In the original paper, the authors performed the reaction using commercially available bakers yeast from a supermarket or bakery. Initially a trial run using similar quantities of Sigma dried yeast resulted in an extremely vigorous initial fermentation, so the quantity of dry yeast was reduced by factor of 5. The contributors assessed the enantiomeric excess of the alcohol by formation of the (+)-MTPA ester and examination of the 19F NMR spectrum. However, the value obtained for the optical rotation was consistent with that reported in the literature. 

Two separate solutions of Red Star active dry yeast (or other supermarket variety, 20 g) and sodium alginate (5g) each in water (200 mL) were prepared by very slow addition of the respective reagent to the rapidly stirred solvent. 

Active composting, 25 874 Active dry yeast (ADY), 26 460-461 Active electroanalytical techniques, 9 568-581... 

Dress shirts (woven), number produced from one bale of cotton, 81331 Drewplus, commercial defoamer, 8 24 It Dried food, rehydration of, 12 85 Dried gels, 23 56-58 Dried yeasts, food uses for, 26 474... 

Inabenfide, 73 43t, 53 Inactive dried yeasts, food uses for, 26 474 InAsSb alloy, superlattices in, 22 159. See also Antimony (Sb) Arsenic (As) Indium (In)... 

Installation qualification (IQ), 11 48 in fine chemical production, 11 433 Instant active dry yeast (IADY), 26 461 Instant coffee, 7 257, 260-262... 

When in later years Krebs reviewed the major points which had to be established if the cycle was to be shown to be operative in cells, the obvious needs were to find the presence of the required enzymes and to detect their substrates. As the substrates are present in the cycle in catalytic amounts their accumulation required the use of inhibitors. Krebs also stressed that rates of oxidation of the individual substrates must be at least as fast as the established rates of oxygen uptake in vivo, an argument first used by Slator (1907) with reference to fermentation A postulated intermediate must be fermented at least as rapidly as glucose is. (See Holmes, 1991). This requirement did not always appear to be met. In the early 1950s there were reports that acetate was oxidized by fresh yeast appreciably more slowly than the overall rate of yeast respiration. It was soon observed that if acetone-dried or freeze-dried yeasts were used in place of fresh yeast, rates of acetate oxidation were increased more than enough to meet the criterion. Acetate could not penetrate fresh yeast cell walls sufficiently rapidly to maintain maximum rates of respiration. If the cell walls were disrupted by drying this limitation was overcome, i.e. if rates of reaction are to be... 

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