Yeast is a living single-cell fungi used in the production of beer. Yeast is added to sweet wort after cooling to initiate the fermentation process. During fermentation, yeast cells convert simple sugars such as glucose into carbon dioxide and alcohol. Fermentation can take anywhere from a few days to several weeks to complete. The type of yeast and particular strain of yeast used can have a large impact on the flavor and aroma of your beer. When possible, it is best to choose a yeast strain that is appropriate for the style of beer you are brewing.
Yeasts come in three basic types - top fermenting ale yeast and bottom fermenting lager yeasts. Of the two, ale yeast are most commonly used for homebrewing because it can be fermented at room temperature.
- Top Fermenting Yeast - Commonly called ale yeast formally known as Saccharomyces cerevisae are fermented at or just below room temperature (10-25 C). These yeasts rise during fermentation and form a foamy head at the top of the fermentation vessel. They also produce a strong estery flavor that is a key characteristic of ales. Stouts, Porters and all forms of Ale are made with top fermenting yeast.
- Bottom Fermenting Yeast - Called lager yeast formally known as Saccharomyces uvarum is fermented at low temperatures in the range of 7-15 C. Lager yeast grows slowly and tends to settle at the bottom of the fermenter because of the cold temperature. Bocks, Pilsners, Marzens and popular American lagers are made with this type of yeast.
- Bavarian Wheat Yeast - Used in Bavarian style wheat beers - known formally as Torulaspora delbruechii is a yeast that produces a distinct bannana or clove like flavor profile that is characteristic of the Bavarian Wheat Beer.
Yeast can be purchased in two basic types:
- Liquid Yeast - Liquid yeast is cultured yeast stored suspended in a liquid form. Liquid yeast is generally of higher purity and quality than comparable dry yeasts, and is a significant favorite with discriminating homebrewers. Packaging on liquid yeast varies. The two most popular forms are a plastic tube, and the smack-pack. The smack-pack form has a built in starter with a small packet of yeast in the middle. By pressing firmly on the package you can release the yeast into the starter hours in advance of brewing to give your yeast a head start. Liquid yeast should be stored in your refrigerator (not the freezer!) as it only has a shelf life of a few months.
- Dry Yeast - Dry yeast is sold in packets just like bread yeast in the grocery store. The yeast is made by dehydrating yeast cells. Dry yeast must be rehydrated by adding water before it is used. Dry yeast has a long shelf life of 1-2 years.
- BeerSmith Yeast Table
- [Add your yeast article here]