Tempeh Making

Tempeh is a chunky, tender soybean cake, especially popular on the island of Java, Indonesia as a staple source of protein. Tempeh making is a natural culturing and controlled fermentation process that binds whole soybeans, sometimes mixed with other grain such as rice or millet, to form a rich cake with a smoky or nutty flavor.

As in most fermentations of food, tempeh making needs a starter. Tempeh starter is a dried mixture of live Rhizopus spores with substrate, either soybeans or rice. To produce good quality tempeh you need a starter with a very high count of desirable Rhizopus molds and contain no contaminating, coliform or pathogenic bacteria. Tempeh can be produced by two Rhizopus strains: Rhizopus oryzae or Rhizopus oligosporus.

Traditional starter in tempeh making is either a piece of the previous day batch tempeh or one especially made by placing a handful of cooked soybeans inoculated with the previous day batch tempeh between two perforated banana, teakwood or hibiscus leaves, allowing them to incubate for a few days until black spores cover the beans, and finally drying them in the sun. The latter is used by rubbing the leaves above the soybeans to be inoculated. Although this type of tempeh starter can easily be contaminated with other molds or bacteria, the climatic conditions in Indonesia are so ideal for tempeh fermentation that this type of contamination is not known to cause problems. In Western countries, however, tempeh making always use pure cultures to ensure consistent quality and to minimize failed batches.

Tempeh making starts with soaking, de-hulling, and partly cooking the whole soybeans. Soaking is done for 6 to 18 hours. To de-hull and split, the beans are squeezed with kneading motion and rinsed clean with water. In Indonesia, traditional tempeh makers soak the beans in a river and stomping them with their feet in large bamboo woven baskets submerged in the river to de-hull.

Cooking is done for about 30 min or till al dente, then the water is drained off but the heating is continued for a few minutes on medium heat to dry the cooked soybeans. Then they are allowed to cool down to below 35°C before mixing in the starter.

A mild acidulent, usually vinegar, may be added either while soaking or before boiling to lower the pH and create an environment that favors the growth of the tempeh mold over competitors. Spread in thin layer, the beans are fermented for 18 to 36 hours at around 30°C (86°F).

Due to its climate, in Indonesia tempeh making doesn’t need incubators. The inoculated beans is simply buried under a pile of leaves to keep it warm and, if necessary, fanned to cool it off.

In good tempeh, the beans are knitted together by a mat of white mycelia to form a compact cake. Under 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.

You can do your own tempeh making. The starter, you may get it over the internet at http://www.tempeh.info. For 250 g of soybeans you need about 3 table spoons of white vinegar and 1 teaspoon of tempeh starter. Use perforated cling film, or perforate empty milk or juice carton, zip-lock sandwich bags or ordinary plastic bags as the packaging. The holes should be thick (about 0.6 mm in diameter) at a distance of about 1 cm to allow the mould to breathe. Press the mix flat to total thickness of max 3 cm. Place the packed beans in an incubator at 30°C (86°F) or at a warm place for about 36- 48 hours to allow fermentation to take place.