Tempeh

What is tempeh

Tempeh is a traditional soy product originating from Indonesia ¹. It is made by a natural culturing and controlled fermentation process that binds soybeans into a cake form. In the US, tempeh is produced by growing mold on soybeans. The soybeans are soaked in water, dehulled and then cooked in boiling water before being inoculated with Rhizopus moulds starter culture and fermented. During fermentation, the soybeans become bound together in a solid mass. The raw unpasteurized tempeh is then packaged, frozen, and shipped to consumer to be sliced, cooked in soup, fried or roasted. The fungus present in tempeh is consumed directly after cooking.

The traditional product is highly perishable and is usually consumed the day it is made. In industrial production, it can be preserved by drying or freezing (after blanching to inactivate the Rhizopus mycelium and its enzymes.)

Tempeh is consumed daily by millions of people in Indonesia and to a lesser extent in the United States and in Europe. Thus, it is clear from the long history of widespread consumption that there is a general recognition of the safety of Rhizopus spp. starter culture for use in food.

Tempeh is naturally gluten free because it doesn’t contain gluten. Gluten is the name given to the protein found in some grains like wheat (including wheat varieties like spelt, kamut, farro and durum, plus products like bulgar and semolina), barley, rye and triticale.

Freshly made, raw tempeh remains edible for a few days at room temperature. The tempeh is neither acidic nor does it contain significant amounts of alcohol. Tempeh does, however, possess stronger resistance to lipid oxidation than unfermented soybeans, due to its antioxidant contents.

Figure 1. Tempeh

Tempeh nutrition facts

Typically, tempeh contains 35% dry matter, half of which is protein and tempeh does not contain salt. The soy carbohydrates in tempeh become more digestible as a result of the fermentation process. In particular, the oligosaccharides associated with gas and indigestion are greatly reduced by the Rhizopus moulds. In traditional tempeh-making shops, the starter culture often contains beneficial bacteria that produce vitamins such as B12 (though it is uncertain whether this B12 is always present and bioavailable) ². In western countries, it is more common to use a pure culture containing only Rhizopus oligosporus, which makes very little B12 and could be missing Citrobacter freundii and Klebsiella pneumoniae, which have been shown to produce significant levels of B12 analogs in tempeh when present ³. The fermentation process also reduces the phytic acid in soy, which in turn allows the body to absorb the minerals that soy provides.

Table 1. Tempeh nutrition facts

[Source ⁴]

What is tofu ?

Tofu is the representative of the “bean curd” foods, the most popular type of traditional soy protein products. Tofu is made by coagulating soy milk and then pressing the resulting curds into soft white blocks. The whiteness of tofu is ultimately determined by the soybean variety, soybean protein composition and degree of aggregation of the tofu gel network. The yellowish beige color of soybeans is due to the color compounds including anthocyanin, isoflavones and polyphenol compounds therefore the soybean variety used can predict the color of the final tofu product. Ways to reduce the yellow color include reducing isoflavone content by changing the pH of the soymilk solution used in the production of tofu so that they precipitate out and are removed during the extraction of soy pulp. The opacity of tofu gel and off-white color typical of standard uncooked firm tofu is due to the scattering of light by the colloidal particles of the tofu. The addition of higher levels of calcium salts and high protein content contributes to forming a denser and more aggregated gel network which disperses more light resulting a tofu with a whiter gel appearance ⁵.

The production of tofu essentially consists of:

1. the preparation of soymilk
2. the coagulation of the soymilk to form curds
3. the pressing of the soybean curds to form tofu cakes.

The typical tofu making procedures are cleaning, soaking, grinding beans in water, filtering, boiling, coagulation, and pressing.

Coagulation of the protein and oil (emulsion) suspended in the boiled soy milk is the most important step in the production of tofu. This process is accomplished with the aid of coagulants. In the case of salts, the positively charged ion in the particular salt reacts with the various protein in the soy milk causing the proteins to precipitate with the oil to form a curd. Coagulation of the soymilk is the most important step in tofu making process but is complicated as the process depends on complex interactions with many variables including the variety and percentage of protein in the soybeans used, slurry cooking temperature, coagulation temperature, and more factors relating to the processing.

Two types of coagulants (salts and acids) are used commercially.

• Calcium sulfate (gypsum): The traditional and most widely used coagulant to produce Chinese-style tofu, it produces a tofu that is tender but slightly brittle in texture.
• Magnesium chloride and calcium chloride: Both of these salts are highly soluble in water and affect soy protein in the same way.
• Glucono delta-lactone (GDL): A naturally occurring organic acid also used in cheese making, this coagulant produces a very fine textured tofu that is almost jelly-like. It is used especially for “silken” and softer tofus, and confers an almost imperceptible sour taste to the finished product.
• Other edible acids: Though they can affect the taste of the tofu more, and vary in density and texture, acids such as acetic acid (vinegar) and citric acid (such as lemon juice), can also be used to coagulate soy milk and produce tofu.

Tofu can be soft, firm, or extra firm. Tofu has a subtle flavor and can be used in savory and sweet dishes. It is often seasoned or marinated to suit the dish.

Bean curd (tofu) has been prepared and consumed in China for thousands of years and a written record of its preparation dates from the second century B.C.

Tofu has been made in the U.S.A since the beginning of the century, as an ethnic food. Its consumption in the West increased rapidly since the 1970s , mainly as a vegetarian alternative to meat and cheese or as a novel food by itself. The development of a highly successful tofu-based all-vegetable ice-cream was a significant factor in the recent growth of tofu production in the West. Today, a variety of types and brands are available in most supermarkets.

Figure 2. Tofu

Table 2. Tofu nutrition facts

[Source ⁴]

1. Tempeh. Wikipedia. https://en.wikipedia.org/wiki/Tempeh[↩]
2. Allison A. Yates. “National Nutrition and Public Health Policies: Issues Related to Bio-availability of Nutrients When Developing Dietary Reference Intakes. http://jn.nutrition.org/content/131/4/1331S.full.pdf[↩]
3. Keuth S, Bisping B. Vitamin B12 production by Citrobacter freundii or Klebsiella pneumoniae during tempeh fermentation and proof of enterotoxin absence by PCR. Applied and Environmental Microbiology. 1994;60(5):1495-1499. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC201508/[↩]
4. United States Department of Agriculture Agricultural Research Service. USDA Food Composition Databases. https://ndb.nal.usda.gov/ndb/search/list[↩][↩]
5. Maltais, Anne; Remondetto, Gabriel E.; Gonzalez, Rolando; Subirade, Muriel (2005). “Formation of Soy Protein Isolate Cold-set Gels: Protein and Salt Effects”. Journal of Food Science. 70: C67.[↩]