Manufacture
While the process is secret, the general method for making yeast extract on a commercial scale is to add salt 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, and since yeast cells have thick hull walls which would detract from the smoothness of the end product, the husks are sieved out. As with other yeast extracts, Marmite contains free glutamic acids, which are analogous to monosodium glutamate (MSG).
Today, the main ingredients of Marmite manufactured in the UK are glutamic acid-rich yeast extract, with lesser quantities of sodium chloride (table salt), vegetable extract, niacin, thiamine, spice extracts, riboflavin, folic acid, and celery extracts, although the precise composition is a trade secret. By 1912, the discovery of vitamins was a boost for Marmite, as the spread is a rich source of the vitamin B complex; vitamin B12 is not naturally found in yeast extract, but is added to Marmite during manufacture. With the vitamin B1 deficiency beri-beri being common during the First World War, the spread became more popular.
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