The most exciting part of making tempeh? It takes place the morning after you’ve boiled and hulled and dried and packed and incubated your beans. That’s when you pull them out of their incubator and savor the fine white film that’s grown over the beans, binding them together into a solid cake. Yep, that’s mold. Take a big sniff and savor its faint yeastiness. It’s the reward for all your hard work. And it’s going to taste amazing.
A staple of the Western vegetarian’s diet, tempeh comes to us from Indonesia, where the fermentation process traditionally involves a banana leaf and tropical humidity. These days, you’re more likely to find these live-culture bean cakes vacuum-sealed between the Not-Dogs and Soysage at your favorite natural-food store. When crumbled and pan-fried, it browns up nicely and makes a satisfactory substitute for ground beef in tacos. Or you can sauté it with broccoli for a stir-fry, use it in a meatless Reuben, or glaze it with maple syrup, toss in some kale, and enjoy your healthy one-pan meal.
For years, I got along fine with the store-bought stuff. Then I started reading about live foods. Sourdough bread, beer, yogurt—and, of course, tempeh—are “living” in that their tastes and textures have been transformed by the processes of microbial organisms. In our germ-phobic world, buying spores to sprinkle over your food so it gets moldier feels like breaking a taboo; it also makes for some experiments that taste way better than anything you’d buy at the store. “I have nothing against the frozen version [of tempeh],” Sandor Ellix Katz writes in Wild Fermentation, the bible for us DIY microbial experimenters, “but it is what I call a vehicle food, only as good as the flavors you smother it with.” Having recently made a couple of batches of tempeh in my cluttered and emphatically nonprofessional kitchen, I can vouch for the homemade stuff being both not too tricky and worth your while. It’s got a subtle flavor and a less chewy texture, and makes for a fun kitchen project to boot.
Tempeh can be made from black beans, black-eyed peas, barley, peanuts, or any combination of various grains, nuts, seeds, and beans. The classic version (and pretty much everything found in grocery stores) uses soybeans, though this isn’t necessarily the easiest variety to make at home. For one, dried soybeans are relatively tough to find, although they’ll usually turn up at Asian grocery stores. For another, they’re almost always sold with their hulls on. When making tempeh, the hull is the enemy. It traps moisture, which can encourage malevolent mold to ruin a perfectly good batch. (The mold you want, Rhizopus oligosporus, is white and smells faintly mushroomy; bad mold is slimy and sticky, and smells like ammonia.)
If your beans aren’t hulled, you’ve got to hull them yourself. Doing this by hand is squishy and tedious; you probably have better things to do with your time. A better bet is to run the dry beans through a flour mill, or some other machine that will split them into halves or thirds without pulverizing them. When boiled (more on that in a bit), the beans’ hulls will rise to the surface where they can be skimmed off. Or just start out with hulled (or split) beans and make your life much easier. For my first batch, I de-hulled soybeans by hand; for my second, I opted for a bag of split chickpeas from Punjab Groceries in Waverly and cut my prep time in half. Four pounds of dried beans yield seven pounds of tempeh, enough to last even the most rabid tempeh fan a couple of months.
Whatever beans you use, they should be cooked until they’re barely soft. For soybeans, this will take about an hour and a half at a rolling boil, maybe a little less if you’ve soaked the beans overnight. Other beans are much faster—after a five-hour soak, the split chickpeas needed only a 10-minute boil. When in doubt, undercook, since fermentation completes the cooking process. I recommend using this bean-boiling pause to brag to your friends about your in-process tempeh. Everyone’s going to be real impressed.
But let’s not get ahead of ourselves. Before you proceed, the beans need to be cool and dry. After straining them, spread the beans out on paper towels or clean kitchen towels to absorb excess moisture. If you’re bored, pat them dry to move the process along. (Katz, who encourages you to “swaddle” your beans at this point, notes, “It is rare that we have the opportunity to be so intimate with soybeans. Enjoy it.”) Don’t rush this step—you want the beans as dry as possible. Remember: Good mold tastes great. Bad mold makes you sick.
Consider using this time to prepare your tempeh container. You want the beans spread in a thin layer with access to some air circulation; I prefer a bunch of Ziploc bags with holes punched in them, but you can also use a large baking pan covered in foil that you’ve perforated.
Once your beans are satisfactorily dry, it’s time to mix in the spores. This is the most difficult part of making tempeh, because it involves planning ahead. And unless there’s a local live-culture merchant I don’t know about, you’ve got to get them via mail order. I bought my R. oligosporus from GEM Cultures, a family-owned business that’s so hippie-fied that it doesn’t take online orders, though it does have a web site (gemcultures.com). The Tempeh Lab, run out of the famed Tennessee commune the Farm, is another reliable source for packets of spores (call  964-3574). GEM sells 11-gram packets, enough for two seven-pound batches, for $3 plus shipping. Sprinkle the spore powder on the dry beans and stir to make sure it gets evenly distributed. Then spoon the beans into your prepared container—they shouldn’t be much more than an inch deep.
Now the little guys have to incubate at 85 degrees for 24 hours. If it was July or you were living in Indonesia, you could just leave your tempeh near a sunny window. Otherwise, you might have to stick the tempeh in a gas oven with just the pilot light on (prop the door open a bit so air can circulate), or make a DIY incubator out of a Styrofoam cooler and a light bulb (just Google it). After a day, the beans should be bound together into a solid cake. Hold it in your hand and feel that heft. Congratulations, you’ve made tempeh. Sauté it right away or store it in the fridge (for a couple of weeks) or the freezer (for a couple of months). Your food is alive. Savor those microbes.