Wash soy beans very well. Soak beans overnight in a large bowl with plenty of water so they stay completely submerged as they absorb.
Drain and rinse the beans. Fill the bowl of beans again with water and massage the bean between your fingers and palms to release the skins. Stir to bring the skins to the top of the water and pour out the skins carefully keeping the beans in the bowl. Repeat this process until the majority of the skins are removed.
In a large pot, boil the beans in plenty of water for 1 hour. Place the lid on half way and watch carefully to prevent them from boiling over.
After 1 hour drain and pour beans into a large bowl. Pat and toss the beans with a clean towel until they are dry.
With a toothpick, poke multiple holes in two 1 quart sized zip lock baggies. Space holes about 1 inch apart.
Add the apple cider vinegar and tempeh starter to the beans and stir until well combined.
Add the beans evenly to the baggies. Zip the bags closed and press them flat. They should not be more than 1 inch thick when spread out flat in the bag.
Place the bags flat on a baking sheet and place them in the oven with the oven light on.
Allow them to ferment for 12 hours and then flip the bags over. And let sit for another 12 hours.
At this point, 24 hours in, there should be white cultures forming on the beans. Flip the bags one more time and turn off the oven light.
Let sit in the oven for another 24 hours.
Now your tempeh should be done fermenting. Your beans should be covered in the white culture and fairly firm.
Cut the baggies off the tempeh bricks and wrap them with cling wrap. Put them into a larger baggie.
You can store the tempeh in the fridge for up to one week or freeze them for up to three months.
Recipe by Meatless Makeovers at https://www.meatlessmakeovers.com/homemade-tempeh/