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Tempeh is a fermented soyfood, very commonly made with okara in Indonesia. Unlike yogurt, tempeh does not require rigid sterility or temperature control for success; but it takes several days to ripe, instead of several hours.
You need a starter or ragi tempeh to make the tempeh. You can buy it from GEM Cultures or The Farm. To make your own starter from your ripe tempeh, cut off the black patches of sporulation and save them in plastic freezer bags in the refrigerator or freezer for your next batch of tempeh. To use, grind the spores with the vinegar in a mortar and add to the okara just as a commercial starter. You have to be more careful and thorough about mixing than with a powdered commercial starter.
Using a commercial starter, add 1½ tablespoons white vinegar and ½ teaspoon commercial tempeh starter to 3-4 cups of okara from 1½ cups dry soybeans. Mix well. Put the mixture into glass or stainless steel loaf pans and tamp it down a bit with the back of a fork. It should end up about an inch thick. DO NOT USE aluminum loaf pans!!! Put foil over the pans and with a pin poke little holes in the foil about an inch apart. <>You have to incubate it at a steady warm temperature. Stick it in the oven over the warmth of the pilot light (or into some other incubator). Leave a note on the oven so you remember the tempeh is in there. There's no problem with taking a batch out in the middle of its process. Just keep it away from the oven and let the oven cool off before putting it back in.
Check the tempeh by looking under the cover after 24-36 hours. It will show a cloud of white over the cake of okara. Once the fungus takes hold, it will start generating its own heat. If it feels hottish, move it a little away from directly over the pilot light. When a good amount of black patches (sporulation, darkness below the white clouds of mycelium) begin forming, you can take it out of the oven. It's not very sensitive about being left in longer than this, the flavor does get stronger because you get more spores. It may smell slightly acid or ammonia coming out of the pans, especially if they are made of iron. After it has been in the fridge a day it will smell sweet.
The solid cake should pop right out of the pan. Cut it in serving size chunks (the size of a chicken thigh) and store in a bag or other closed container in the fridge. Will keep up to two weeks in the refrigerator. If you need more help or information on making tempeh, or want tempeh recipes or supplies, I recommend you visit Peter's site on how to make tempeh.
May be eaten as is, but best cooked up in your favorite sauce.