Compressed yeast is a yeast compound used for baking and creating yeast-based, or rising, foods. Most commonly used to create bread and bakery products, yeast creates the rise in dough that allows a flat ball of ingredients to become a puffy finished loaf. Yeast is sold in many different varieties; compressed yeast, while valued by some for its active performance, can be difficult to store and care for, and has a very short shelf life.
Yeast is a fungus originally collected by brewers as a by-product of beer making and sold to bakers to make bread. This one-celled fungi is an active little beast; when combined with carbohydrates such as gluten, it creates bubbles of carbon dioxide that get trapped in the dough's elastic structure, causing a loaf to rise. Since it is necessary to nearly every leavened bread product, the creation, packaging and storage of yeast is extremely important.
Compressed yeast is sold in blocks or bricks, featuring a high moisture content that must be carefully monitored. Typically found in the refrigerated section of grocery stores or bakery supply outlets, compressed yeast, also known as cake yeast, must be kept cool in order to remain viable. Some bakers swear by the excellent rise and flavor given by compressed yeast, but others bemoan the finicky conditions and short two to three week shelf life.
Fresh compressed yeast is cream-colored or beige, and has both moist and crumbly properties. If the yeast has turned brown or shows any signs of mold, it is generally too old and should be discarded. To check if compressed yeast is still active, try crumbling a small piece into a glass of slightly warm water; if bubbles begin to rise after a few minutes, the yeast is still fairly active.
If purchased in fresh, refrigerated cakes, yeast does not usually need to be proofed before use. Some dried compressed varieties do require proofing in warm water before adding to dough. Proofing essentially wakes up the yeast and activates it, beginning the process of creating carbon dioxide. In order to proof dried compressed cakes, crumble yeast in slightly warm water and allow to sit for several minutes.
To store compressed yeast correctly, try wrapping the cake in several layers of plastic wrap then cover them in tinfoil. Yeast should be kept in a cool part of the refrigerator for up to three weeks. Compressed yeast can also be frozen for about a year, but should be used immediately upon defrosting for best results.