Tempeh - Production

Production

Tempeh begins with whole soybeans, which are softened by soaking, and dehulled, then partly cooked. Specialty tempehs may be made from other types of beans, wheat, or may include a mixture of beans and whole grains.

A mild acidulent, usually vinegar, may be added to lower the pH and create a selective environment that favors the growth of the tempeh mold over competitors. A fermentation starter containing the spores of fungus Rhizopus oligosporus is mixed in. The beans are spread into a thin layer and are allowed to ferment for 24 to 36 hours at a temperature around 30°C (86°F). In good tempeh, the beans are knitted together by a mat of white mycelia.

Under conditions of lower temperature, or higher ventilation, gray or black patches of spores may form on the surface—this is not harmful, and should not affect the flavor or quality of the tempeh. This sporulation is normal on fully mature tempeh. A mild ammonia smell may accompany good tempeh as it ferments, but it should not be overpowering. In Indonesia, ripe tempeh (two or more days old) is considered a delicacy.