Saccharomyces cerevisiae

What the species is

Saccharomyces cerevisiae is a single-celled budding yeast. It grows as small round cells that reproduce by budding and convert sugars into ethanol and carbon dioxide. In a dough or a wort it is the organism that does most of this conversion, which is why it is the yeast of bread, most wine and ale.

The name refers to a species, not to a strain. Bakers' yeast, wine yeast and ale yeast are all S. cerevisiae, yet they differ in the sugars they use, their tolerance of salt, sugar and cold, and the aromas they leave in the product. A bakery strain is therefore described by its use and its strain code, not by the species name.

Bread, dough and the sugar it needs

Maltose is the main sugar in bread dough. Amylases in the flour release it from starch, and glucose and fructose are scarce in most doughs. Baking strains are therefore adapted to use maltose through the MAL gene loci, and commercial baking strains often carry several copies of them.

Dough is a hard environment for yeast: its semi-solid structure and high salt or sugar content create osmotic stress. Glycerol production helps cells survive, and some glycerol leakage softens the dough and improves gas retention, while too much harms aroma. Trehalose and proline protect cells during freezing and drying, which is why cryotolerant strains are sought for frozen dough.

Leavening, sugar and timing

Dough rises because yeast turns sugar into carbon dioxide and ethanol. When glucose is present, glucose repression can push metabolism toward ethanol rather than gas, which delays the rise. Attempts to raise CO2 output by changing single metabolic enzymes have generally failed, because the gains cost other traits such as growth yield.

A 2020 survey cited in the review found that sourdough and commercial baking strains produced more CO2 and had shorter lag times than non-bakery strains. This is one reason baker's yeast is a distinct product from a wine or ale strain.

Domestication and strains

The review describes baking strains as polyphyletic, which its authors link to at least two domestication events, and most surveyed bakery isolates are European. Tetraploidisation appears to have happened at least once in commercial baking strains. Brewing and wine strains come from separate lineages, and the species has been moved into beer and wine work for many centuries; the sources do not establish one date for when it was first used in either.

Brewers have also worked with the related lager yeast, Saccharomyces pastorianus, which is a hybrid rather than this species alone; it has its own page.

Notes

The bread-yeast review focuses mainly on Western bread and European baking strains and does not cover every baking tradition. Strain names and their performance in a given recipe come from the producer or culture collection and are not established by the species name.