Yeasts are single-celled microorganisms classified as members of the fungus kingdom. They are more than 1,500 species currently identified. The word “yeast” comes from Old English gist, gyst, and from the Indo-European root yes, meaning “boil”, “foam”, or “bubble”.
How Yeast Works
Through the process of fermentation, yeast converts sugars into carbon dioxide and alcohol. These two byproducts make yeast an extremely useful tool in food production. Consequently, carbon dioxide is what gives alcoholic beverages such as beer and champagne their characteristic bubbles and is also responsible for rising bread.
As yeast begins to metabolise sugars in bread dough, the carbon dioxide gas is trapped within the gluten strands, creating bubbles, and causing a leavening action. In beverages, the carbon dioxide is trapped within the liquid by the pressure of the sealed container.
Yeast microbes are probably one of the earliest domesticated organisms. Archaeologists digging in Egyptian ruins found early grinding stones and baking chambers for bread, as well as drawings of 4,000-year-old bakeries and breweries [Planets in a Bottle]. However in 17-century scientists observed yeast under the microscope, but at the time they did not consider them to be living organisms [Yeast]. Furthermore, in 1857, Louis Pasteur proved that alcoholic fermentation was conducted by living yeasts.
Culinary uses for yeast
Beer: Yeast is added to malted grains and allowed to ferment in order to produce alcohol. The type of yeast used will affect the type and flavour of beer produced. There is three kind of methods to ferment beers with different yeasts.
- Top fermenting or top cropping, ferments at a higher temperature and produces sweet or fruity beers.
- Bottom fermenting or bottom croppers, ferment at lower temperatures and are used to make lagers.
- Spontaneous fermentation is historically brewed in Brussels without any yeast inoculation.
Wine: Yeast is naturally present on the skins of grapes (wild yeast) and can be used to naturally ferment grape juice (must) into wine. Despite the naturally present yeast, most wines today added to them to produce a more consistent and controllable result.
Bread: Records of using yeast as a leavening agent date back to the ancient Egyptians, though the form of yeast used has changed over time. Many varieties are available for use in bread making, such as fresh yeast cakes, bakers yeast, active dry, instant, or yeast starter. The same yeast is not used to ferment beer or whiskey or to make bread.
The benefits of yeast
These microorganisms are indispensable elements and play a crucial role in our diet and balance. Raw yeast is not recommended for consumption in quantity as it can proliferate within your body, but once pasteurised, yeast offers a host of nutritional benefits. Yeast is a good source of protein, B vitamins, and minerals.
Researchers have selected specific strains to make beer, wine, spirits and industrial ethanol (including ethanol-based fuel). The different strains of yeast for alcohol thus have their specific features to adapt to certain substrates (fruit, grapes, grain, beet, malt), enhance particular flavours in the finished product, adapt to certain temperatures, resist high or low temperatures, etc. Scientists from the University of British Columbia, Canada, have found a new strain of yeast that has reduced amines. The amines in red wine and white wine produce off-flavors and cause headaches and hypertension in some people [Eureka! Vancouver scientists take the headache out of red wine].