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The bun also rises with freeze-hearty yeast.

The bun also rises with freeze-hearty yeast

There's nothing quite as deflating as baking a bread that never rises because the yeast in the dough has lost its zest. The problem has inspired the Montreal-based Lallemand, Inc., a company that grows and sells yeast to companies that make frozen doughs, to attempt to develop freeze-and thaw-resistant strains of yeast. The demand for such yeast and for frozen dough is expanding, says Chris Toupin at St. Hyacinthe Food Research Center in Quebec. Bakeries and restaurants can store large amounts of one batch of dough for long periods of time, using it only as needed; proprietors want to know that the quality of the resulting breads and croissants will be consistent.

So Lallemand's Pierre Gelinas, Toupin and their colleagues varied the conditions under which Baker's yeast is cultured until they found the one that produced the most hearty strain. The yeast was stored in miniature doughs at -30[deg.]C for up to six months, and then the volumes of the dough were compared when they were subsequently cooked.

In order to understand why some strains survived freezing and thawing while others died, the researchers examined the permeability, flexibility and composition of the yeast membrane. They discovered that the heartiest yeast is most permeable to water. This probably allows water to move out of the yeast quickly during freezing, says Toupin, so that damaging ice crystals do not form inside the yeast cells. In addition, having flexible membranes also appears to help the yeast cells survive the large changes in volume that accompany freezing and thawing and that can often kill or compromise a cell.

Toupin says that there are differences in the amount of one type of lipid that makes up the membrane of the yeast, but his group has yet to completely understand the link between composition and behavior of the membrane.

The best part of this research, adds Toupin, is that he and his co-workers get to eat the baked results of their experiments.
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Author:Weisburd, Stefi
Publication:Science News
Date:Jul 4, 1987
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