Tempeh is a traditional fermented Indonesian soy food prepared from soaked and cooked soybeans by salt-free aerobic fermentation using the mold Rhizopus oligosporus, a fungus. During the fermentation, the dense cottony mycelium produced by Rhizopus binds the soybeans together to form a compact cake. This page has a selection of excellent and informative articles about tempeh.
Tempeh has excellent nutritional value — much better than tofu, also made from soybeans, because tofu is more highly process and to some degree refined. In terms of nutritional value, edamame (steamed soybeans) is better than tofu, and tempeh is better than edamame.
In my experience, homemade tempeh is much better than packaged tempeh I buy in a store — plus it’s satisfying to grow your own, as it were.
I started a while back, and I’ve gradually identified the success factors. Here’s a summary of my lessons learned and the method I now use:
- I often use soybeans, but you can use instead (or in addition) black beans, kidney beans, pinto beans, and so on. You can mix in cooked intact whole grain (spelt, kamut, brown rice, black rice, or the like) or boiled raw peanuts. Avoid using spices, many of which have anti-fungal properties (one reason they are used in making foods such as sausage: the spices act as a preservative).
- Cook beans without using baking soda or salt, and I don’t bother removing the hulls from soybeans. (Removing the hulls (skins) from soybeans is Indonesian practice; Malaysians don’t do that. I follow Malaysian practice because a bean’s skin has good nutritional value.) Cooking method: Soak beans overnight, drain soaking water using a sieve, then put the beans in a pot and cover well with water and simmer until done. I’ve found that beans are not so apt to boil over if I don’t cover the pot. However, with the pot uncovered, it is necessary to add water during cooking because of evaporation. I usually use 2 cups of uncooked beans for a batch.
- Rhizopus prospers in an acidic environment, and that is achieved by using vinegar (apple cider, white, brown rice, and wine vinegar all will work: the acidity is what’s important). You can choose between two times to add the vinegar: (a) toward the end of cooking (for the last 15-20 minutes or so), in which case add 2 tablespoons of vinegar per cup of uncooked beans (thus I add 1/4 cup vinegar for my 2-cup batch) and continue cooking until beans are done; or (b) after the beans have been cooked, drained, dried, and cooled, in which case use 1 tablespoon per cup of uncooked beans (2 tablespoons for my 2-cup batch).
- The best way I’ve found to dry the cooked beans is to drain them through a sieve and then spread them on a clean dishtowel. Dry them with a paper towel, pressing the beans gently and rocking them back and forth. You can also use a hair-dryer to help, but be careful not to get too close or the blast of air will blow the beans off the towel. Rhizopus likes a little moisture but definitely not so much that the beans are wet.
- Leave the beans on the towel until they’ve cooled. The common advice is to let them cool to 95ºF (35ºC), but it’s simpler just to let them cool until they are close to room temperature. Being cooler is not an issue, since they’ll warm up as you incubate them.
- After the beans have been dried and cooled, put them into a bowl. If you’re adding vinegar using method (b), add 1 tablespoon of vinegar per cup of uncooked beans. Then add either one packet of tempeh culture or — presumably — a chunk of tempeh from the previous batch, chopped up and mixed in. I still need to experiment with the latter.
- You can spread the beans in a layer in a flat glass dish, but I generally use a Ziploc fresh-produce bag because those bags are nicely perforated for ventilation. They’re also a good size for a 2-cup batch: if the beans are spread evenly through the bag lying on its side, the layer is a nice thickness.
- Incubation can be done initially in an oven on the proofing setting (if your oven has that) or in an oven with the light on and the door slightly open. For various reasons I decided to build my own tempeh incubator using rigid 1″ foam insulation board (sold in 24″ squares for projects; 3 square will make an excellent incubator — details at the link). I lay the bag on a raised rack over a seedling warming pad (see link), which has a thermostat so I can regulate the temperature.
- Incubate at 88ºF (31ºC) until Rhizopus is well started. This will take at least 12 hours and maybe 24 or even 36. Eventually you will see white patches of mold — it will look as though the bag has some steam inside. At that point reduce the thermostat to 77ºF (25ºC) and allow the batch to continue to work for another 24-48 hours. For the first few batches I did not reduce the temperature, and as a result the mold spored, which produces dark grey or black areas. The tempeh is still good and perfectly edible, but some find the black spots off-putting. That hasn’t happened since I started reducing the temperature once the mold is established.
- When you consider the batch done, remove the block of tempeh from the bag and cut into pieces that will fit your storage containers and refrigerate it.
I usually cut off a piece and fry it like a hamburger patty in a little olive oil and use it to top a dish. I also make tempeh breakfast sausage. Sometimes I cut a portion into pieces and use them in a stir fry.
Here’s a batch in process in my homemade tempeh incubator. This is after about 12 hours at 77ºF (25ºC).