Active dry yeast

A wide variety of products can be produced by fermentation. In some cases the microorganism itself is the product, for example, in the manufacturing of active dry yeast (ADY). Well-known pharmaceutical fermentation products are insulin and penicillin G. Fermentation processes are also used to produce various commodity bioproducts like organic and amino acids, polysaccharides, lipids, chemical compounds like isoprene (Whited et al., 2010), 1,3-propanediol (Nakamura and Whited, 2003), RNA, DNA, enzymes, and other proteins. The large variety of commodity bioproducts produced by fermentation requires an equally large variety of different methods to separate and purify them. Compared to fermentation processes, where usually one unit, the fermenter vessel, is used, several different steps and unit operations are necessary to achieve purification and formulation of bioproducts. 

To emphasize the large variety of downstream processes and the importance of integrated process development between fermentation, recovery, and formulation, four bioprocesses are briefly discussed below. 

An example of a commodity bioproduct everybody has probably encountered is ADY. In this case, the cells are the product. The downstream processing for ADY can consist of several washing steps and concentration by centrifugation. The washing steps remove the fermentation media from the yeast cells. The yeast cream obtained by centrifugation is further concentrated using a filter-press to produce a yeast cake. Extrusion and drying of the yeast cake yields the final ADY product. 

All the processing steps that are done after the yeast cream is generated serve only one purpose water removal. The water removal steps are neeessary to stabilize the active yeast cells. Additional processing steps are costly, but the yeast cream has a short shelf life compared to the dried product. 

One important factor when drying yeast cells is intracellular trehalose. The intracellular trehalose content is considered a critical determinant of stress tolerance in yeast (Nishida et al., 2004). Trehalose is a nonreducing a-linked disaccharide commonly found in any hydrobiotic organisms. When phospholipid membranes are dried, the temperature at which the gel to hquid crystal phase transition occurs increases (Crowe et al., 1984). It has been shown that trehalose interacts with model membranes during drying and lowers the dry membrane phase transition temperature (Crowe et al., 1986). 

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

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. 

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. 

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... 

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

Querol, A., Barrio, E., Huerta, T., and Ramon, D. (1992). Molecular monitoring of wine fermentation conducted by active dry yeast strains. Appl. Environ. Microbiol. 58, 2948-2953. 

The fermentors used in most regions are stainless steel tanks, although wooden barrels are still widely used in Sauternes and Tokaj. The addition of thiamin (0.6 mg/1), diammonium phosphate (300 mg/1), and active dry yeast (10-15 g/hl) is recommended to achieve an optimal fermentation rate, more rapid yeast propagation and reduce SO2 requirements (Dubourdieu, 1999 Hoersch and Schlotter, 1990). 

Inoculation of the juice with active dry yeast is preferred to minimize the production of undesirable odors. Generally, Saccharomyces bayanus is... 

Chewing gum base 0.01% by weight of chewing gum base Active dry yeast or dry material... 

Steveninck, J. V. Ledeboer, A. M. (1974). Phase transitions in the yeast cell membrane—the influence of temperature on the reconstitution of active dry yeast. Biochim. Biophys. Acta 352,64-70. 

Fermichamp. [Gist-Brocades Food Ingreds.] Instant active dry yeast for vinification. 

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