Yeast extract

Yeast extract is the common name for various forms of processed yeast products that are used as food additives or flavourings. They are often used in the same way that monosodium glutamate (MSG) is used, and, like MSG, often contain free glutamic acids. The texture ranges from liquid to a light paste. (Herbst p.681) Glutamic acid in yeast extracts are produced from an acid-base fermentation cycle, only found in some yeasts, typically ones bred for use in baking.

Autolyzed yeast

Autolyzed yeast or autolyzed yeast extract consists of concentrations of yeast cells that are allowed to die and break up, so that the yeasts' digestive enzymes break their proteins down into simpler compounds.

Yeast autolysates are used in Vegemite (Australia), Marmite, Promite, Oxo (New Zealand, South Africa, United Kingdom, and Republic of Ireland), and Cenovis (Switzerland). Bovril (The United Kingdom and Republic of Ireland) switched from beef extract to yeast extract for 2005 and most of 2006, but later switched back. Autolyzed yeast extract is also the primary source of monosodium glutamate for the food industry.

Hydrolyzed yeast or hydrolyzed yeast extract is another widely used food additive, used for flavouring purposes.

Manufacture

The general method for making yeast extract for food products such as Vegemite and Marmite on a commercial scale is to add sodium chloride to a suspension of yeast making the solution hypertonic, which leads to the cells shrivelling up; this triggers autolysis, in which the yeast self-destructs. The dying yeast cells are then heated to complete their breakdown, after which the husks (yeast with thick cell walls which wouldn't do the texture much good) are separated.