Foolproof Tempeh—Lessons from Experience

Black-bean-&-black-rice tempeh — photo by author

Tempeh is a traditional Indonesian and Malaysian food made by fermenting cooked beans (traditionally, soybeans) with a fungus. During fermentation, the dense cottony mycelium of the fungus binds the beans together to form a compact cake. This page has a selection of informative articles about tempeh.

Using a fungus to make a food is not unusual. Bread and wine, for example, are made using yeast, a fungus. A fungus (Penicillium camemberti) forms the coating on Camembert and Brie, and Roquefort is made using Penicillium roqueforti. Tempeh uses the fungus Rhizopus oligosporus.

Tempeh cooks well, tastes good, and is highly nutritious — much more nutritious than tofu, also made from soybeans, because tofu is more highly processed and refined. Edamame (cooked fresh soybeans, a whole food) is more nutritious than tofu, and tempeh is more nutritious than edamame (because tempeh includes both the beans and the mycelium of the fungus).

When we think of eating fungi, we normally picture mushrooms, the “fruit” produced by the mycelium, the main body of the fungus — a mushroom is to a fungus what an apple is to an apple tree. In the case of tempeh, we eat the mycelium itself, and we avoid having the fungus spore because sporing results in gray or black patches on the tempeh (perfectly edible but somewhat off-putting). The goal is to grow the snow-white mycelium without having it spore.

I make Malaysian-style tempeh, leaving the soybean hulls in place. (Indonesian-style tempeh removes the hulls.) I leave the hulls on because (a) it’s easier, and (b) the hulls have nutritional value.

Normally, the beans are cooked and then wrapped in banana leaves or a perforated plastic bag. (I find Ziploc fresh-produce bags perfect for the purpose since they are already nicely perforated.) However, you can also make tempeh by spreading the beans in an open flat dish, perhaps with tented foil above it, leaving it unwrapped. That method gives the fungus free rein, and it goes a little feral, growing long fuzz. When the beans are wrapped (in a banana leaf or fresh-produce bag), the wrapping tames the fungus so that it produces a soft, velvety, white coating similar to that found on Camembert.

Making tempeh at home lets you create combinations you can’t find in a store — for example, black-bean-&-black-rice tempeh (photo above; great in chili and stir-fries); or chickpea-peanut tempeh (photo below; good in a curry or a stir-fry). My current batch uses soybeans and unpolished kodo millet, one of the best millets. I buy unpolished millet (that is, the whole grain with the bran intact) because (a) polished millet tends to clump when cooked, and (b) it’s not so nutritious as unpolished. Polished millet, like white rice or pearled barley, is not an intact whole grain but has had the bran removed. The Harvard School of Public Health notes:

The bran is the fiber-rich outer layer that supplies B vitamins, iron, copper, zinc, magnesium, antioxidants, and phytochemicals. Phytochemicals are natural chemical compounds in plants that have been researched for their role in disease prevention.

Chickpea-peanut tempeh after it’s finished. I’m cutting it to fit the glass storage container. — photo by author

I had to experiment a fair amount before I could produce batches of good tempeh on purpose. Now that I’m gone through (and learned from) common mistakes and figured out a reliable method, I wanted to document it so others can build on my experience. (BTW, if you think of a particular combination of beans and grain that sounds good to you, let me know in a comment. I’m always looking for ideas for intriguing tempeh.)

Discoveries from trial and error

Some of the things I discovered by trying them:

  • Do not mix spices or herbs with the beans before culturing. Spices and herbs tend to be anti-fungal, one reason they’re used in food preservation — as in summer sausage, for example. On the other hand, you can add spices and herbs to your heart’s content after the tempeh is made — as a marinade (e.g., tempeh bacon) or spices mixed in (e.g., tempeh sausage).
  • Do not add a little baking soda to the cooking water for the beans. Baking soda (about 1 teaspoon per cup of dried beans) makes the beans cook quicker, be more tender, and keeps the skins from splitting — all good, but the tempeh fungus requires an acidic environment. If the beans are alkaline (as from baking soda in the cooking water), the fungus will sicken and die.
  • Do not maintain a constant temperature of 88ºF (31ºC) after the initial stage of fermentation. That temperature works well to start the culture, but once the fungus is established and traces of mold begin to appear, the temperature must be lowered, otherwise the fungus will start to spore. The sporing bodies form gray or black patches — edible but unsightly. Once the tempeh fungus has taken hold (12 to 24 hours after starting it), remove the batch from the incubator and put it on a raised rack to continue fermentation at room temperature.

If your home is chilly, you can continue using an incubator if you reset the thermostat to 77ºF (25ºC). However, for a large batch — my batches from 3 cups of uncooked beans, for example — the fungus generates plenty of heat and should just be taken out of the incubator or oven and allowed to ferment at room temperature until it’s ready to be cut up and refrigerated in a storage container. The raised rack is important to ensure air flow around the batch.

A good way to dry and cool the beans: After the beans have cooked so they’re just tender, drain them in a sieve and spread them in a single layer on a clean dishtowel to dry. They will be hot, which helps the drying. Take a paper towel and use it to press and rock the beans gently from side to side. You can also carefully use a hair dryer—“carefully” because if you’re not careful, you blow beans about the kitchen. (I did use a hair dryer on my latest batch, and it does a good job. I was careful.)

Use a clean dishtowel rather than a paper towel when you spread the beans, because when the beans have cooled, a dishtowel allows you to pick them up (by holding the dishtowel at the corners) and dump them into a bowl to mix in the tempeh culture. A paper towel would just fall apart.

Beans cool quickly when they’re spread in a single layer. It’s okay for them to cool even to room temperature since they warm up quickly in the oven or incubator, as explained below.

Here are the steps to make your own tempeh.

Step 1. Choose the ingredients.

Pick the kind of beans you like and that fit recipes you have in mind. Soybeans are great, and I make soybean tempeh often, but I also like to use other beans (black, pinto, garbanzo, or kidney beans, for example). I generally include a second ingredient—most often cooked intact whole grain (black/forbidden rice, kamut, spelt, red fife wheat, whole rye, or hulled barley, for example). I’ve also used peanuts as a second ingredient — see photo above. I cook beans and grain separately, then combine them in a bowl when I add the tempeh culture (and possibly vinegar — see Step 2).

Besides beans and (optionally) grain, the only ingredients are vinegar and tempeh starter culture.

Step 2. Cook, dry, and cool beans (and grain if using).

Beans and grains have different cooking times, so cook them separately. I normally make a 3-cup batch, which I measure before I cook. I start by measuring 3 cups of uncooked beans, or 2 cups of uncooked beans and 1 cup of grain, though I might not use all the grain. (Obviously, 3 cups of uncooked beans will make more than 3 cups of cooked beans — 1 cup of uncooked beans will make about 3 cups when cooked, and grain also expands when cooked.)

Cook grain
Grain usually is cooked to absorb all the cooking water, so no drying step is needed, though the grain must be cooled. I cook the grain first and let it cool (and absorb any remaining traces of water) while I cook the beans.

Cook beans
Soak beans in plain water for 8 hours or so (overnight, for example), then drain them, add fresh water to cover by an inch or so, and simmer until the beans are tender. I have found that if I simmer the beans uncovered, they are much less likely to boil over, though then I do have to keep an eye on the water level. I add water during cooking as needed.

Dry and cool
Dry the beans and grain after cooking. Rhizopus likes a little moisture but definitely not so much that the beans are wet. As noted above, I drain the beans through a sieve and then spread them on a clean dishtowel to dry and cool. The common advice is to cool them to 95ºF (35ºC), but it’s simpler just to let them cool until they are close to room temperature.

Step 3. Create an acidic environment for the fungus.

Rhizopus prospers in an acidic environment, which you get by using vinegar (apple cider, white, brown rice, or red or white wine vinegar—any will work: the acidity is what’s important).

You can choose one of two times to add vinegar to the beans:

(a) toward the end of cooking (for the last 15–20 minutes), in which case add 2 tablespoons of vinegar per cup of uncooked beans (thus I add 1/4 cup vinegar for a 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 add 1 tablespoon per cup of uncooked beans (2 tablespoons for a 2-cup batch).

When I use grain with the beans, I add vinegar to the grain at the end, after it has dried and cooled: 1 tablespoon for a 1-cup batch of grain.

Step 4. Add the tempeh culture and bag the beans (and grain if used).

After the beans (and grain) 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 (and 1 tablespoon for 1 cup of grain, if you’re using it).

Then add one packet of tempeh culture, a little at a time, stirring the beans with a soft spatula to mix well. (I think that I could probably start a batch by taking a chunk of tempeh from the previous batch and mixing it with the bean and grains. I still need to experiment with that to test the idea.)

As noted above, you can spread the beans in a layer in a flat glass dish, but I use a Ziploc fresh-produce bag because those bags are nicely perforated for ventilation. Those bags are also a good size for a 2-cup or 3-cup batch. If the beans are spread evenly across the bag lying on its side, so that the bag is filled side to side and top to bottom, the layer has a nice thickness. I prefer the thickness of a 3-cup batch because a section of that is easy to cut into thinner slabs — the slab from the 2-cup batch is a little too thin to slice into thinner slabs.

Here’s the batch of chickpea-peanut tempeh right at the start, immediately after bagging it. This was a 3-cup batch: 2 cups chickpeas, 1 cup raw peanuts (which I cooked by boiling).

Chickpea-peanut tempeh immediately after bagging it in a fresh-produce bag. — photo by author

Step 5. Incubate the batch to get the fungus going, then transfer the batch to the countertop to finish.

Initial incubation can be done 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; three square provide enough, once cut, to make an excellent incubator — details at the link). I lay the bag on a raised rack over a seedling warming pad whose thermostat lets me regulate the temperature

Incubate at 88ºF (31ºC) until Rhizopus is well started. This will take 12–24 hours. Eventually white patches of mold will appear — it will look as though there are steamy spots inside the bag (see photo below, taken 24 hours after the photo above). At that point if your house is chilly, reduce the thermostat to 77ºF (25ºC) and allow the batch to continue to ferment for another 24–72 hours. I’ve found, however, that a 3-cup batch generates so much heat that it must be removed from the incubator and put it on a raised rack on the counter to continue fermentation.

I’ve found that 3 1/2 days total (1 day to start the batch in the incubator and 2 1/2 days on the counter on a raised rack) seems to be enough, but you can experiment with longer fermentation.

Chickpea-peanut tempeh with fungus established. This is ready to leave the incubator. — photo by author

Sometimes gray areas will appear on the bottom of slab as it sits on the counter. These are where the fungus has just started to spore. When I see that, I turn the slab over (still in the Ziploc bag), and the gray areas are soon overgrown with new snow-white mycelium. I typically turn the slab about every 8 hours or when I notice any gray spots.

Step 6. When the tempeh’s done, cut it into sections and refrigerate

Once you decide that the batch is done, remove the block of tempeh from the bag. I cut the bag apart to do this since the tempeh grows tightly inside the bag. Once you have the slab of tempeh free, cut it into pieces to fit your storage containers and refrigerate it. The chickpea-peanut slab below has just been removed from the bag after a total fermentation time of 3 days 7 hours.

The finished chickpea-peanut tempeh, removed from the bag. — photo by author

Use in cooking

Tempeh is cooked before serving, and it can be cooked in various ways. I cut off a piece that’s a good size for whatever I’m going to make, and then I cut that up:

  • Dice it bite-size for chili, curry, stir-fry, stew, or soup.
  • Dice it small for quick cooking — for example, sautéed with a little olive oil, a chopped tomato, and chopped onion, perhaps with a pinch of Mexican oregano and smoked paprika, and use that in a dinner bowl.
  • Slice a slab into two or three thinner slabs, fry those in olive oil, then sprinkle with salt and cut into squares to serve as croutons in a salad or as a topping for soup. Or marinate thin strips cut from the slab and make tempeh bacon.
  • Mince it to use as an ingredient, as when you make tempeh sausage.

Tempeh works well with a marinade if you have time, though I generally just chop and cook.

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