Yeast is a live culture that is used in baking, cooking, and brewing. But not all types of yeast are created equal. Each type has its own characteristics that suit a certain application. While some types of yeast can be used interchangeably if you tweak the recipe, others are so different that they don't work for all purposes. So it is important when shopping for a particular recipe to make sure you buy the right version.
Types of Yeast Used in Baking
When making bread and certain baked goods, yeast acts as one of the leavening agents during the fermentation process. "Baker’s yeast" is the general term given to all forms of Saccharomyces cerevisiae used to make bread products. Baker’s yeast is available in several forms such as active dry, fresh (or cake), liquid, and instant.
Before adding to a recipe, this type of yeast requires dissolving in a warm liquid to activate it, unlike instant yeast which is added directly to the recipe ingredients. Active dry yeast should not be exposed to liquids hotter than 110 F (43 C) or else it will kill off the yeast. This yeast is usually sold in 1/4-ounce envelopes or 4-ounce jars (once the jar is open, store in the refrigerator).
Fresh or Cake
Fresh yeast is sold in compressed or cake form. This type of yeast is extremely perishable, so it must be kept refrigerated and used within a couple of weeks of purchase. When using fresh yeast, it is dissolved into a liquid prior to adding to a recipe.
Fresh yeast should be proofed, or tested for potency, before each use. To proof yeast, dissolve in warm water and add a pinch of sugar. If the yeast does not begin to foam within 5 to 10 minutes, it is no longer active.
This was the most popular form of yeast in the early 19th century, prior to the invention of compressed or cake yeast. Liquid yeast is basically a slurry of live yeast organisms, flour (or other carbohydrates), and water, similar to a sourdough or bread starter. As long as fresh carbohydrate is added on a regular basis, the organisms will continue to live and replicate.
Instant yeast is the most active form that's commercially available. This yeast does not require dissolving into a liquid before adding to a recipe and often only needs one rise. This form of yeast is very shelf-stable and can be stored in a dry, airtight container at room temperature until the expiration date. Instant yeast is also called rapid rise or bread machine yeast. (Labeling instant yeast as “bread machine yeast” makes it easier for consumers to choose the correct yeast to use in their bread machines.)
Types of Yeast Used in Cooking
Nutritional yeast and yeast extract are used as both a flavoring and to give a healthy boost to recipes. Neither needs to be cooked. Although yeast extract is technically a type of nutritional yeast, it's used in a very different manner. Therefore, they can be treated as two separate products.
A deactivated form of yeast, nutritional yeast is commonly used in vegan recipes and is a good source of minerals and B vitamins, hence its name. Nutritional yeast is sold in flake, granule, or powder form and has a nutty or cheese-like flavor. It is often used as a topping or seasoning for foods and as a nutritional supplement. The fact that it is a deactivated yeast means it is okay to consume large quantities; eating live yeast organisms can lead to proliferation throughout the body.
This concentrated nutritional yeast product is often in the form of a paste. Yeast extracts are favored for their pungent, umami flavor. They have a wide variety of uses and have developed a cult following around the world. Popular brands of yeast extract include Marmite and Vegemite.
Types of Yeast Used in Brewing
Brewer's yeast is the variety used to make beer. There are two types of yeast used to make beer, one for brewing ale and one that makes lager.
Also known as ale yeasts, top-fermenting yeast rises to the surface during the fermentation process of beer-making, which creates a rich, thick head. This yeast should be used at warm temperatures ranging from 50 to 77 F (10 to 25 C). Ale yeast produces additional flavors and creates a beer in a matter of days.
Bottom-fermenting yeast is also known as lager yeast, which should be used at cooler temperatures, between 44 to 59 F (7 to 15 C). The yeast grows more slowly than the top-fermenting kind, meaning lagers take weeks to develop, and doesn't create much foam. It also settles to the bottom of the fermenter as the process ends.