Asian ferments like tempeh often seem intimidating to new fermenters, but are actually quite easy once you’ve sourced the cultures you need to make them. In this post, I’ll share step-by-step instructions for making tempeh at home, including photos detailing the process. I hope I can alleviate some of your fears because homemade tempeh has a delicious, mushroomy flavor that is delightful! 🙂
Making Tempeh At Home
Tempeh is an Indonesian staple of fermented soybean cake made with a culinary mold. Partially cooked soybeans are inoculated with the spores of Rhizopus oligosporus, wrapped in a bundle, and left at a warm temperature for the mold to grow. The thready mold fills the spaces around the soybeans forming a firm cake, and rendering the beans easier to digest and more nutritious. Making tempeh is actually quite simple, but there are two challenges: 1. One must acquire spores from a reputable source to make tempeh at home, and 2. Tempeh must be incubated at 85°F to 88°F to culture successfully.
Purchasing Tempeh Spores
In the U.S we have few suppliers of tempeh spores so many people have them shipped in from overseas. At the recommendation of a friend I purchased spores from The Tempeh Starter Store and I have been very pleased. They processed my order right away, emailed me shipping confirmation, and provided a tracking number for my package. It was well wrapped and arrived quickly and in good condition. The spores themselves have performed very well, growing quickly and making a solid tempeh cake in about 24 hours.
Rhizopus oligosporus is the traditional tempeh culture. It makes classic tempeh with good flavor and the tempeh will sporulate and turn dark around the edges if you let it incubate long enough. Another culture available is Rhizopus oryzae. This culture makes a milder tasting tempeh and will not sporulate to form gray or black spots even with a long incubation time. Rhizopus oryzae might be closer in flavor to commercial tempeh purchased in the U.S. I use this Rhizopus Oligosporus culture.
In Indonesia, tempeh can be left out in the warm air culture naturally, but if you don’t live in a warm climate you’ll need some kind of small box with a heating element and thermostat. When I first started making tempeh, I tried my oven with the light on, but it wasn’t warm enough. Check yours with a temperature probe to see if it will work. I also attempted making tempeh in my Excalibur dehydrator, but the lowest temperature setting is 95°F, which is too warm, and the fan dried out the edges of the cake.
So I began shopping to build my own incubation chamber. For this you will need: small cooler, seedling mat with adjustable thermostat, remote probe thermometer, and small rack to keep tempeh elevated above heat source. Adding up the price of all these items new, I found it would cost me about $60USD to make a tempeh incubator. For me it made more sense to purchase a Brod & Taylor Folding Proofer. This proofer can maintain a temperature between 70°F-120°F, has a steaming tray, and folds flat for storage. I use it for tempeh, yogurt, and sourdough, and also to temper chocolate when making Christmas candies and melting shea butter and bees wax for homemade lotions and salves. It’s been a great purchase for me, but if you prefer something cheaper and enjoy thrift shopping do an Internet search of “DIY tempeh incubator” for tips on making your own. 🙂
Makes 2 Tempeh Cakes
1lb. dry soybeans
Plenty of fresh water
½tsp. tempeh spores
2 sandwich-size zip-top baggies
Pick over and rinse the soybeans, then place them in a large bowl and add fresh water to cover by 3-4″. Allow them to soak overnight or at least 12 hours. Soybeans have a thick hull that is difficult for the culinary mold to penetrate. After the beans have soaked, use your hands to very gently massage them, rolling them around in your fingers to loosen the skins. Then drain and rinse the beans and transfer them to a large stockpot.
Add fresh water to the pot to cover the beans by 3-4″. Cover and bring to a boil. Once the beans are boiling, the loose skins will rise to the surface with the foam. Skim all the foam and skins from the surface and discard them. A few beans may also be removed, which is fine.
Continue simmering the beans until they are just al dente. Beans for tempeh should not be cooked until soft, because they will soften more during culturing.
Pour the beans into a colander, rinse with fresh cool water, and drain well. Fold a clean bath towel in half and set it on your workspace. Pour the beans onto the towel and spread them out.
Fold the edges of the towel over the beans and gently pat and roll them around. This step helps to loosen up any remaining hulls. Beans for tempeh should not be wet. Spread them into a single layer to dry for a bit.
Transfer the beans to a large mixing bowl. Add 2tsp. vinegar and stir to mix. A little vinegar acidifies the mixture to prevent growth of pathogens. Next, mix in the ½tsp. tempeh starter. Toss the beans well to distribute the spores evenly.
Spoon the inoculated beans into 2 sandwich-size zip-top baggies. Try to make them even. 🙂
Squeeze out excess air and seal the bags. Then gently pat them into flat cakes. Use a fork to poke many holes all over the baggies. Tempeh mold needs oxygen to grow. If the cakes are too moist or lack oxygen, the beans will turn slimy instead of growing tasty mold.
Place the bean cakes in the incubator and set the temperature between 85°F and 88°F. It may take a few batches to find the right temperature for your incubator in your house. 86°F works well for me, but you may need to go a little higher. In my Brod & Taylor Folding Proofer, I find it’s necessary to elevate the tempeh from the heat source with a second rack.
Check your tempeh after 12 hours. You may find the first white threads of mold growth are starting to appear. Flip the cakes now. They may be warm to the touch. Tempeh mold generates its own heat as it grows. This is why it’s important to have a thermostat that can turn the heat source off and on as needed.
At 24 hours there should be a lot of mold growth. Flip your tempeh again. It may be ready. Tempeh is done when the white mold forms a solid mass and holds the beans together in a firm cake. As it ages, if you bought spores of Rhizopus oligosporus, the mold may form gray or black spots near the ventilation holes. This is normal and healthy, but the flavor of the tempeh will be a little stronger. These dark spots are new spores forming.
When the tempeh is ready, transfer it to the fridge. It is a perishable food and should be eaten in 3-5 days or frozen for longer storage. Tempeh should be cooked before eating. Cut the tempeh into slices and fry in coconut oil for a quick and tasty meal. YUM! 😀
Once you’ve mastered making tempeh with soybeans, you can try other kinds of beans, and even add hearty whole grains. I’ve successfully used black-eyed peas, fava beans, and chickpeas. Be sure to report back with any tasty new experiments.
Wild Fermentation, by Sandor Katz
The Art of Fermentation, by Sandor Katz
The Book of Tempeh, by William Shurtleff & Akiko Aoyagi (also available for free online)