For our first attempt at mold fermentation, we decided to make tempeh. I bought the tempeh starter at a local co-op. This starter from Cultures for Health contains rhizopus oryzae cultures, although it seems like rhizopus oligosporus is the more common type used.

Step 1: Soaking and De-hulling – We started off by soaking 2 cups of dried soybeans overnight, then de-hulling them by breaking them open in our hands. This method of de-hulling seemed pretty inefficient, since the hulls didn’t come off easily after soaking. Maybe we didn’t soak them long enough. In The Art of Fermentation, Sandor Katz suggests cracking the dried soybeans using a hand grinder before soaking. Since we don’t have a hand grinder, we thought about running the beans through a food processor briefly next time before soaking.

Step 2: Boiling – After de-hulling, we boiled the soybeans until they were soft enough to bite through (about 20 min). We did skim out some of the hulls that rose to the top, but Katz does say that “removed from the beans, the hulls do not impede development of the mold, and they add fiber and bulk to the tempeh” (286).

Step 3: Drying – The next step was to dry the beans after draining the water—either by patting them with a clean towel or warming them in the pot on low heat. We used paper towels (bad idea), next time we will warm them in the pot. Drying is important because wet beans encourage bacteria growth instead of the rhizopus mold.

Tip: Don’t use paper towels to dry the soybeans. It doesn’t work that well

Step 4: Cooling – We let the beans cool to 95-98°F.

Step 5: Add starter and vinegar – The acid from the vinegar provides “better growing conditions for the mold and suppression of contamination or toxin production” (286). In traditional tempeh-making, the beans are soaked for around 24 hours and this soak allows for lactic acid fermentation, but this acidification doesn’t happen as quickly in cooler climates.

Step 6:  Prepare container and fill – We used compostable re-sealable plastic bags, and punched holes 1 inch apart using a thin nail.


Step 7: Culture at 85-91°F for 24-48 hours – The first 12 hours need assisted heat, but after that the fermentation will generate its own heat. We turned our oven into an incubator by placing an incandescent bulb inside. We placed the packs over a pan of water hopefully to keep the space humid enough.

Here is the tempeh after 24 hours. The “dark patches” (spots in this case) are “the first signs of sporulation” and that is when the tempeh is ripe. The dark spots usually first occur where the holes are since that is “where airflow is greatest and the surface becomes driest” (289).

We had to leave town immediately after the tempeh was done, but thankfully, you can freeze it. I just defrosted it in the fridge when I came back. Here is the first thing I made with the tempeh.

Both of us agreed, this homemade tempeh (even after a week in the freezer) was better than any store-bought tempeh we’ve ever gotten!