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Yeast extracts consist of the cell contents of yeast without the cell walls; they are used as or flavorings, or as nutrients for bacterial culture Growing media. They are often used to create savoury flavors and umami taste sensations and can be found in a large variety of packaged foods including frozen meals, crackers, snack foods, gravy, stock and more. They are rich in B vitamins (but not B12). Yeast extracts and fermented foods contain glutamic acid (free glutamates), an amino acid which adds an umami flavor. Glutamic acid is found in meat, cheese, fungi ( and yeast) and vegetables—such as broccoli and tomatoes. A number of other substances found in yeast extract provide aromas, some meat-like, when allowed to react under heat.
The heat-autolytic process to make yeast extract of the autolysate type was invented in the 19th century by Justus von Liebig. Yeast cells are heated until they rupture, then the cells' own digestive break their down into simpler compounds (amino acids and peptides), a process called autolysis. The insoluble cell walls are then separated by centrifuge, filtration, and usually spray drying.George A. Burdock, Encyclopedia of Food and Color Additives 3:2972, CRC Press, 1997, This is the process used for Vegemite, Marmite, and the like.
Yeast extracts in liquid form can be dried to a light paste or a dry powder. This is not the same as nutritional yeast, which are made from intact cells not directly hydrolyzed and consequently have a lighter flavor.
In terms of fermentation, spent beer yeast is commonly contaminated with the bitter compounds from hops, requiring a "debittering" step to wash out most of this undesired flavor. Yeast from other sources are not affected by this issue. Spent brewer's yeast is also quite biodiverse, containing yeasts other than traditional Saccharomyces cerevisiae and sometimes beer spoilage-causing lactic acid bacteria too.
For disruption of the cell, some physical and chemical methods may be used in place of the heat-autolysis process. Doing so may allow specific compounds to be extracted or to produce an extract without the hydrolysis of cell contents (as in autolysis) happening. Autolysis can be assisted with added enzymes; for example, additional nuclease would enhance the release of nucleosides from RNA.Eisenbrand, Gerhard & Peter Schreier9783131434623 ISBN 9783131434623
Separation removes insoluble parts, mainly the yeast's cell wall, from the extract. Cell wall is usually sold in two parts: the glucans as "yeast β-glucan" and the mannans further processed into mannans-oligosaccharide (MOS). The product is finally concentrated by drying, into a thick paste or a dry powder.
Yeast extract products derived from plant feedstock are by definition vegan and kosher–pareve, although some consumers prefer extra certification. They are also generally considered halal, despite the concern that the yeast has come into contact with alcohol.
Yeast extract is used as a flavoring in foods. It is a common ingredient in American barbecue-flavored such as Lay's. It is also widely used in .
In Australasia and the Pacific, British Marmite is sold as "Our Mate", due to the presence of a licensed Marmite produced in New Zealand.
A spread for sandwiches, toast, crumpets and cracker biscuits as well as a filling for pastries, Vegemite is similar to Marmite, New Zealand Marmite, Australian Promite, MightyMite, AussieMite, OzEmite, Brazilian Cenovit, German Vitam-R and Swiss Cenovis.
Vegemite is salty, slightly bitter, , and rich in glutamates giving it an umami flavour similar to Bouillon cube. It is Veganism, kosher and halal.
Marmite has been manufactured in New Zealand since 1919. The product's popularity in England prompted the Sanitarium Health Food Company to obtain sole rights to distribute the product in New Zealand and Australia in 1908. They later began manufacturing Marmite under licence in Christchurch, albeit using a modified version of the original recipe, most notable for its inclusion of sugar and caramel. Common ingredients are also slightly different quantities from the British version; the New Zealand version has high levels of potassium, for example. New Zealand Marmite is described as having a "weaker" or "less tangy" flavour than the British version.
Cenovis is popular in Switzerland (particularly Romandie). It was developed in Rheinfelden in 1931, on the initiative of a master brewer named Alex Villinger, (French) and was subsequently produced by the company Cenovis SA.
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