What Is Yeast?

All about yeast - description, how it works, and uses.

Fresh and dried yeast
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In the culinary world, yeast has a wide variety of applications. For thousands of years, yeast has been used to produce carbonation and alcohol, leaven breads, and provide nutritional supplementation.

What Is Yeast?

Yeast is a single-celled organism with over 1,500 species known. Saccharomyces cerevisiae is the species most widely used in food production. Yeasts used in food production prefer warm, moist growing environments with a slightly acidic pH.

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.

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 metabolize 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. When the container is opened, the pressure is released and the carbon dioxide begins to release or bubble.

Alcohol, the other byproduct of yeast fermentation, is also produced during the bread making process but evaporates as the bread bakes. When making alcoholic beverages, yeast is allowed to ferment for a much longer period of time, allowing it to produce more alcohol.

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 flavor of beer produced. S. cerevisiae, also known as a “top fermenting” or “top cropping” yeast, ferments at a higher temperature and produces sweet or fruity beers. Bottom croppers, such as Saccharomyces pastorianus, ferment at lower temperatures and are used to make lagers.​
  • Wine: Yeast is naturally present on the skins of grapes and can be used to naturally ferment grape juice into wine. Despite the naturally present yeast, most wines today have pure culture (usually S. cerevisiae) added to them to produce a more consistent and controllable result. There are many different strains of S. cerevisiae and each will produce a unique flavor characteristic in a finished wine.​
  • 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.​
  • Nutrition: Raw yeast is not recommended for consumption in quantity as it can proliferate within your body, but once pasteurized, yeast offers a host of nutritional benefits. Yeast is a good source of protein, B vitamins, and minerals. Yeast intended as a nutritional supplement is often sold as “nutritional yeast” or “yeast extract.” Yeast extracts, such as Marmite, have a cult following due to their unique flavor and variety of uses.