What is yeast?
Yeast is a microscopic fungus that metabolizes carbohydrates (sugars) into carbon dioxide gas and alcohols. It is used as a leavening agent in baking (carbohydrates turn into carbon dioxide and cause the dough to expand; the alcohol evaporates during the baking process). Yeast is also used in the fermentation of alcoholic beverages such as wine, beer and spirits (carbohydrates turn into alcohol and the carbon dioxide bubbles through the liquid and dissipates into the air) and nutritional supplements (yeast is an excellent source of protein and vitamins). Yeast can also be further processed into yeast extract which is used as a food additive or for flavorings.
It’s important to note that many of the products that contain yeast can be made with yeast which is naturally present in the environment, but since there are many strains of yeast results can be unpredictable. Therefore, a commercially produced yeast of the best strain for the specific application is typically used.
How is yeast made?
A seed of yeast from the desired strain is fed with nutrients that allow growth. Typically, the main nutrients are sugars; however, vitamins, minerals and other additives are added as well. This process is known as fermentation. At the end of this process, the nutrients and water are removed from the yeast in a centrifuge and the resulting product is cream yeast. The cream yeast can be sold as is or used for further processing.
The cream yeast is dried by filtering moisture out and then it is compressed and sold as fresh yeast or mixed with emulsifier and dried carefully with hot air so the yeast remains active and sold as active dry yeast. Nutritional yeast is dried differently and the yeast deactivates in the process. Brewer’s yeast is yeast that was used in the beer making process and then dried; it is frequently used for yeast extract and nutritional benefits.
Is yeast kosher?
In the USA the sweeteners used for yeast production are mostly molasses and high fructose corn syrup (HFCS) and the main kosher concern is to make sure that they are transported to the facility in kosher vessels. In addition, other sweeteners as well as the vitamins and other additives must be kosher for the finished product to be certified as kosher.
Yeast made from wheat or barley based sweeteners is chometz, while corn based sweeteners make kitniyos yeast. Kosher for Passover yeast (used for wine and yeast extract) is usually made especially for Passover, utilizing only molasses and additives that are kosher for Passover.