Tempeh is a processed food, but it’s one of the most minimally processed options you’ll find. The entire production involves just three steps: cooking whole soybeans, adding a fungal culture, and letting them ferment for one to two days. No preservatives, no flavor enhancers, no chemical modifications. Plain tempeh typically contains only two ingredients: soybeans and a starter culture.
How Tempeh Is Made
The process starts with whole soybeans soaked overnight for six to eight hours to soften them. After soaking, the beans are boiled for about 30 minutes, then cooled. Many producers also dehull the beans at this stage to create a softer texture, though it’s optional. Once cooled to below 35°C, the beans undergo a natural lactic acid fermentation that lowers their acidity, similar to what happens when making yogurt or sauerkraut.
Then comes the step that actually creates tempeh. The beans are spread on trays and inoculated with spores of a mold called Rhizopus oligosporus. Over the next 24 to 48 hours at around 30°C, the mold grows a dense white network of fibers (called mycelium) that binds the beans into a firm, sliceable cake. That’s it. The beans go in loose and come out as tempeh, with a nutty flavor and a firm, slightly chewy texture.
Traditionally in Indonesia, where tempeh originated, the beans ferment wrapped in banana leaves. Commercial producers typically use perforated plastic bags instead, which allow the mold to breathe during fermentation.
Where Tempeh Falls on the Processing Spectrum
This is where things get interesting. The NOVA food classification system, which ranks foods from unprocessed (Group 1) to ultra-processed (Group 4), has placed tempeh in the ultra-processed category in at least one published analysis. A study in the journal Nutrients grouped tempeh alongside canned soups, baked beans, and oral supplements as ultra-processed.
That classification surprises most nutritionists, and it highlights a limitation of the NOVA system: it was designed to flag industrial processing, not traditional fermentation. By NOVA’s strict criteria, any food that involves an industrial technique or added ingredient beyond salt, sugar, or oil can land in a higher processing category. But tempeh’s production is closer to making cheese or sauerkraut than to manufacturing a frozen dinner. The “processing” is biological. A living organism transforms the raw material, and no synthetic additives are involved.
Plain tempeh sold in stores generally lists soybeans, water, and starter culture on the label. Some varieties add rice, barley, or flax seeds to the soybean base, but these are still whole ingredients. Pre-marinated or flavored versions are a different story. Those often include soy sauce, sweeteners, or other seasonings that push them further along the processing continuum.
What Fermentation Actually Changes
The mold doesn’t just hold the beans together. It fundamentally changes the nutritional profile of the soybeans in ways that matter for your body.
One of the most significant changes involves phytic acid, a compound in soybeans that blocks your body from absorbing minerals like iron, zinc, and calcium. Fermentation reduces phytic acid content from about 1.07% in whole dry soybeans to between 0.67% and 0.75% in finished tempeh. That roughly 30% reduction means you absorb more of the minerals present in the food.
Fermentation also dramatically increases the polyphenol content, the plant compounds linked to antioxidant activity. Tempeh contains roughly five times the total polyphenols of unfermented soybeans (6,157 mg per kg versus 1,203 mg per kg). Specific compounds shift in both directions: some increase substantially while others decrease, but overall antioxidant capacity goes up.
Tempeh also provides some vitamin B12, which is unusual for a plant-based food. The B12 is produced by bacteria that grow alongside the mold during fermentation. One study found that a serving of sautéed tempeh can supply about 32% of daily B12 needs. That’s meaningful for people eating plant-based diets, though not enough to rely on as a sole source.
Live Cultures and Cooking
Fresh, unpasteurized tempeh contains live mold cultures and bacteria from the fermentation process. But most commercial tempeh is pasteurized or frozen to extend shelf life, and both treatments reduce the live microbial count significantly. Pasteurization at 100°C for 10 minutes kills most vegetative microorganisms, though some spores survive the process.
Since tempeh is almost always cooked before eating (pan-fried, baked, steamed, or grilled), any remaining live cultures are killed by the heat. So while tempeh is a fermented food, it’s not a reliable source of live probiotics the way fresh yogurt or raw sauerkraut can be. The nutritional benefits of fermentation, like improved mineral absorption and increased polyphenols, remain intact after cooking. The probiotic benefit does not.
Plain Tempeh vs. Flavored Varieties
If your concern about processing is really about additives and ingredient lists, the distinction between plain and flavored tempeh matters more than whether fermentation counts as “processing.” Plain tempeh made from soybeans and starter culture is about as close to a whole food as a fermented product gets. The soybeans are intact, visible, and recognizable in the final product.
Flavored or marinated varieties often add soy sauce (which may contain wheat), sweeteners like maple syrup, spices, and sometimes oil. These aren’t harmful ingredients, but they do move the product further from “minimally processed” territory. If you’re trying to keep your diet as close to whole foods as possible, buying plain tempeh and seasoning it yourself gives you full control.
Compared to plant-based meat alternatives built from isolated proteins, starches, and flavoring agents, plain tempeh is in a completely different category. It’s a whole soybean that’s been cooked and fermented. The beans are still visually identifiable when you slice into it. That’s a useful gut check when evaluating how processed a food really is.