Engineered & Changing Yeasts:
Can yeasts be improved? Most likely work will continue on this process for as long as there are chemists, and geneticists interested in yeasts. One of the more interesting new research areas in this domain is the work on recombinant-DNA technology as it pertains to the development of newer yeast strains. This work has led to changes in formulation, ingredients and processing conditions. Some of this work has led to new strains of yeast which are more resistant to stress, produce more proteins, and more carbon dioxide. Some of the goals of this work are to increase shelf life, dough Rheology and flavor (Randez-Gil et al)
Cauvain and Young describe the changes in yeast pre and post the 1960's. They discovered that in their bread baking processes, the early yeast peaked too soon, and the resultant oven spring was much less than desired. Later yeasts were able to provide the desired gassing power at the time needed in their baking. For example, at the two percent yeast level, pre-sixties gas production from yeast activity peaked at between 70and 80 minutes, decreased between 90 and 100 minutes, then increased again until 200 minutes, finally ending at approximately 10 millimoles of carbon dioxide. Contrary to this, post-sixties yeasts, used at the same 2% level provided a smooth increase in gas production all along the time axis, peaking at 25 millimoles of gas in 140 minutes. This work was in England, and may not seem relevant to bakers in the United States. We do feel, however, that the information provided by the work there, is important to know in order to maintain a more complete picture of the effects of yeast - as well as many other ingredients - on baking.
General Considerations
Yeast produced for different needs may be single strain, hybrid, or mixed strains and propagation profiles. According to Lallemand, North American yeast is optimized for a compromise between lean and sweet dough. When compared with other countries, US and Canadian bakers prefer compressed yeast that is light in color, dry to the touch, and friable (easy to crumble). Artisan bakers in the US and Canada tend to process doughs at temperature of 75 to 90 F, as do artisan bakers in Europe. There is widespread availability of compressed and instant active dry yeast in North America, with a trend toward increasing use of instant active dry yeast.
Also, as presented by Lallemand, Lean dough requires yeast with high maltase enzyme activity, because maltose sugar from flour is the primary energy source. Also important, is the enzyme maltose permease which transports maltose into the yeast cell. Once the maltose is in the yeast cell, the maltase is able to cleave the maltose molecule into two glucose molecules. Straight dough works best with fast yeast that adapts quickly to give good oven spring. Sponge and dough methods work best with slower yeast that retains sufficient activity for the final proof. Fast strain yeast dosages customarily used for straight dough can be reduced for use in sponge and dough methods.
Last Edited on: 12/25/2001 11:31:00 PM