Tempeh is a fermented soy product, a cultured cake of soybeans and grains made by a culturing and controlled fermentation process that binds the soybeans into a very firm cake.
Other types use barley, flax, oats, brown rice, or other grains.
The fermentation process and its retention of the whole bean give tempeh a higher protein content, dietary fiber, and vitamins compared to other soy foods like tofu and a much firmer texture.
Tempeh originated in Indonesia, where it could be considered the oldest food technology in the history of the Javanese people.
The book Serat Centhini — a twelve-volume compilation of Javanese tales and teachings written in 1814 — mentions it, indicating that tempeh had been produced and eaten by the time of its publication.
Food historians believe tempeh may have come from the Chinese making a similar product, soybean koji; soybeans fermented with Aspergillus molds. The Rhizopus starter that tempeh uses could have been due to its better adaptation to the Indonesian climate.
In Europe, this versatile plant protein came from the Dutch, who once colonized Indonesia.
Here in the US, it’s only been known since 1955 when it appeared in Possible Sources of Proteins for Child Feeding in Underdeveloped Countries published in the American Journal of Clinical Nutrition.
The traditional process begins with cracking whole dried soybeans with a grain mill.
Next, the beans are soaked overnight and dehulled to remove the outer covering. After they’re drained and rinsed, the soybeans are placed in a large pot to cook until tender.
Once they’re cool, it’s time to inoculate the soybeans with the Rhizopus oligosprorusstarter.
When complete, the inoculated soybeans incubate for 24 – 48 hours. This time allows the fermentation process to take place and a thick layer of white mycelium mold binds the soybeans into a firm cake.
Don’t worry, the mold (Rhizophus) that is used is considered GRAS (Generally Recognized as Safe) by the US Food and Drug Administration (FDA).
Actually, foods fermented with Rhizophus can be beneficial. The species have been used as a detoxifying agent against food toxins and increase the digestibility of certain legumes. (1, 2)
Finally, the finished fermented cakes are steamed, packaged, and refrigerated ready for a variety of cooking methods.