Tempeh is a popular Indonesian soy bean ferment that could be considered a “meat analog” according to Shurtleff and Aoyagi due to its texture, flavor and protein content. There is some uncertainty regarding the origins of tempeh (Shurtleff and Aoyagi, 1985). The earliest written record of tempeh comes from a compilation of Javanese tales and teachings, written in 1815. However at that time, tempeh was already widely used in Indonesia and estimates as to its origins range from 1600 A.D. to over 2000 years ago. One possibility for the origins of tempeh is that Chinese traders brought soy beans to Indonesia, where they were then used in place of coconuts in a ferment that was already well established (coconut press cake tempeh or Tempe bongkrèk). Alternatively, the Chinese brought both the soy beans and the idea of fermentation, since soybean were already being fermented in China using the Aspergillus mold to make soybean koji, a step in the production of soy sauce. The recipe was then adapted to a mold better suited to the tropical climate of Indonesia.
Tempeh is a firm cake, composed of dehulled soybeans surrounded by the white mycelium of the Rhizopus mold. Tempeh is made by taking soybeans and soaking them overnight in water. The tough outer covering of the beans is then removed and the beans are cooked. Once cooked, they are traditionally subjected to a lactic acid pre-ferment in order to provide a more hospitable environment for the Rhizopus mold, although today this step is often replaced by the addition of an acid, such as vinegar. The soybeans are then inoculated with Rhizopus oligosporus and left to ferment at 30C for 24 hours.
The mycelium, which grows around the soybeans, is the vegetative part of the fungus, and it is responsible for breaking down and absorbing the nutrients of its substrate enabling the fungus to grow. The mycelium secretes enzymes, capable of breaking polymers of lipids, proteins and carbohydrates into their respective monomers. By breaking down the polymers, the fungus renders the soybean more readily digested by humans. In particular, some of the carbohydrates in soybeans which are associated with indigestion are reduced in tempeh.