Baker's yeast
Baker yeast is the common name for the strains of yeast commonly used in baking bread and other bakery products, serving as a leavening agent which causes the bread to rise (expand and become lighter and softer) by converting the fermentable sugars present in the dough into carbon dioxide and ethanol.
[8] Saccharomyces exiguus (also known as S. minor) is a wild yeast found on plants, grains, and fruits that is occasionally used for baking; however, in general, it is not used in a pure form but comes from being propagated in a sourdough starter.
It is generally assumed that the earliest forms of leavening were likely very similar to modern sourdough; the leavening action of yeast would have been discovered from its action on flatbread doughs and would have been either cultivated separately or transferred from batch to batch by means of previously mixed ("old") dough.
Such cultures (sometimes referred to in old American cookery as "emptins", from their origins as the dregs of beer or cider fermentation) became the ancestors of modern baker's yeast, as, in general, they were carefully maintained to avoid what was later discovered to be bacterial contamination, including using preservatives such as hops as well as boiling the growth medium.
[11] While the innovation is often popularly credited for using steam in baking ovens, leading to a different crust characteristic, it is notable for including procedures for high milling of grains (see Vienna grits[12]), cracking them incrementally instead of mashing them with one pass; as well as better processes for growing and harvesting top-fermenting yeasts, known as press-yeast.
Refinements in microbiology following the work of Louis Pasteur led to more advanced methods of culturing pure strains.
[14] Conversely, sorbates do inhibit yeast fermentation activity, so are not added directly to yeast-leavened dough but may be sprayed onto finished products or even incorporated into packing materials.
[18] Though each version has certain advantages over the others, the choice of which form to use is largely a question of the requirements of the recipe at hand and the training of the cook preparing it.
Dry yeast forms are good choices for longer-term storage, often lasting more than a year at room temperatures without significant loss of viability.
[19] In general, with occasional allowances for liquid content and temperature, the different forms of commercial yeast are considered interchangeable.
[citation needed] Because it is readily available and easy to culture, baker's yeast has long been used in chemical, biological, and genetic research as a model organism.
