Tempeh fermentation works best when the substrate combines high protein content, accessible starches for fungal growth, and a particle size that allows even mycelial binding. Historically and practically, several legumes meet these criteria with varying trade-offs in nutrition, texture, and local availability.
Core legumes and why they work
Soybean is the benchmark because its high protein fraction, neutral flavor, and cotyledon size produce a firm, sliceable cake when inoculated with Rhizopus oligosporus. M.J.R. Nout and F.M. Rombouts at Wageningen Agricultural University document soy’s long-standing suitability for tempeh and the conventional processing steps that remove anti-nutritional factors and favor fungal colonization. Soy’s balanced amino-acid profile and the fungus’s proteolytic activity also improve digestibility, making it a top choice for vegan protein production.
Alternatives that perform well
Mung bean and chickpea are commonly used alternatives because their smaller cotyledons and lower lipid content allow rapid, uniform fermentation and a milder, often softer texture. Nout and Rombouts describe successful tempeh made from these legumes, noting adjustments in dehulling and cooking times. Cowpea and adzuki bean produce tempeh with distinct regional flavors and are advantageous where they are agronomically preferred. Faba (broad) beans and certain lupin species can yield high-protein tempeh but may require pre-treatment to reduce bitterness or alkaloids and careful starter strain selection.
Processing choices shape outcomes: dehulling, soaking, and adequate cooking reduce oligosaccharides and trypsin inhibitors while improving substrate accessibility for the fungus. C.W. Hesseltine at the United States Department of Agriculture emphasized the role of starter culture robustness in achieving consistent colonization across diverse legumes. Texture and flavor depend as much on processing and starter strain as on legume species.
Cultural and environmental context matters: soybean tempeh is rooted in Indonesian culinary tradition, but local legumes offer territorial resilience and lower transport-related emissions where soy is imported. Replacing or blending soy with regionally adapted legumes can diversify supply, reduce monoculture pressure, and reflect local taste preferences. The consequence for producers is a choice between the standardized processing benefits of soy and the sustainability and cultural alignment of alternative legumes.