In the Winery
Sugar fungus. . . so what’s in a name?
The common yeast Saccharomyces cerevisiae has been a versatile and very useful companion for humans.
By Gary Strachan
icture this. I had been working with the common yeast Saccharomyces cerevisiae for three years. In an oral examination, I was asked the meaning of its name. Saccharomyces is easy . . . “sugar fungus”, but I drew a blank on the cerevisiae part which simply means “of beer”.
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It could just as easily have been “of bread” or “of wine” because the common yeast of our fermentations has been a human companion throughout all of human history and prehistory, literally millions of years. I suppose that if we track the name back further, the species name is derived from Ceres, the Latin goddess of agriculture, grain crops, and fertility. What an embarrassment! S. cerevisiae is one of the most- studied organisms of genetics. These tiny unicellular things have subcellular organelles and biochemistry similar to mammals, conserved from a time when we had a common ancestor.
It’s a gift to researchers: A tiny, distant relative with a generation time as rapid as 45 minutes. We could use some of its properties. In times of starvation, yeast can protect itself by sporulating. The starving cells use their cell reserves to go through a sexual cell division (meiosis) followed by a normal cell division (mitosis) and the four progeny are wrapped in a protective cover called an ascus.
Spores are a bit like seeds. They can survive high temperature, low
28 British Columbia FRUIT GROWER • Spring 2016
temperature, dessication and starvation for years until the supportive conditions of nutrient, temperature, and moisture are restored. Perhaps that’s what we’ll require for deep space exploration.
Unless you know the species and the strain from the label on the package, you won’t notice a lot of difference between the various species or yeast strains, but there are subtle differences in fermentation performance. Under the microscope, one tiny round cell looks much like another. In winemaking, the usual yeast is S. cerevisiae, and there are thousands of commercial strains of this species.
Oval cells of Saccharomyces cerevisiae, in methylene blue stain, magnified 400 times.
As an alternative, S. bayanus is a popular yeast among both beer makers and winemakers. It contains both lager strains for beer, and champagne strains for wine, is aromatic, and cold tolerant. I like bayanus strains because they
can usually initiate a fermentation under difficult conditions. In contrast to S. cerevisiae, the S. bayanus species is thought to be only about 600 years old and probably evolved within the cool beer making caves of Germany. Apart from Patagonia in Argentina, S. bayanus hasn’t been detected in the wild anywhere else in the world.
S. cerevisiae has a useful inducible gene called invertase. In the presence of table sugar (sucrose), invertase is secreted outside the yeast cells and breaks down sucrose into
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