Tempeh

Tempeh is made by fermenting cooked, split soybeans with a specific mold culture, which grows through the beans and binds them together into a dense, firm cake over roughly a day of warm incubation. The mold's white, cottony growth is what holds the beans together, giving tempeh its distinctive sliceable texture, quite different from the individual grains of loose beans it starts from.

Home tempeh making generally involves cooking and slightly acidifying the soybeans, cooling them, inoculating with tempeh starter culture, packing them into a shallow container or perforated bag, and holding them at a warm, steady temperature for about a day, sometimes longer. A dedicated incubator or a warm oven with the light on are common ways home fermenters maintain that temperature range.

A common mistake is packing the beans too thickly, which traps heat generated by the mold's own metabolic activity and can cause the batch to overheat and fail partway through. Uneven mold growth, with patches of bare bean showing through, often points to soybeans that were not dried enough before inoculation. Following a tested tempeh recipe closely on timing and temperature tends to produce far more consistent results than improvising.