Tempeh and Tofu ,once close relatives derived from the soybean plant, raised and formed for purpose in two different living environments.
Which is healthier? Let's get right down to it: a primer on the soybean.
Tempeh is a whole soybean product with different nutritional characteristics and textural qualities. Tempeh's fermentation process and its retention of the whole bean give it a higher content of protein, dietary fiber and vitamins compared to tofu, as well as firmer texture and stronger flavour.
Tempeh is made through a relatively simple process: the soybean is first made tender through soaking and then it's de-hulled. The beans are partially cooked and then pressed into a layered cake or patty form. There are other forms of tempeh that can be derived from whole wheat or a mixture of soy and grains, yet the most commonly found variation is soy tempeh.
The soy protein in tempeh becomes more digestible as a result of the fermentation process . As a result, tempeh has been known to greatly aid in overall digestive health.
In particular , the oligosaccharides that are associated with gas and indigestion are greatly reduced by the Rhizopus culture. In traditional tempeh making shops the starter culture often contains beneficial bacterial that produce vitamins such as B12.
Tofu is derived from the soybean, yet after the bean has been processed to the soy milk product . In it's simplest form, tofu is to the soybean as cottage cheese is to dairy milk. It is the curd of soy milk pressed into chunks, slabs or bricks. Full of iron and calcium, as well as being cholesterol free, you can see how it serves as a great addition to any diet.
Tofu is low in calories, contains a relatively large amount of iron and contains little fat. Depending on the coagulant used in manufacturing, the tofu may also be high in calcium and/or magnesium. Tofu also contains soy isoflavones, which can mimic natural human estrogens and may have a variety of harmful or beneficial effects when eaten in sufficient quantities.
There is also the issue of phytic acid to consider. A study of phytic acid in soybeans documents in detail the phytic acid level at different stages of preparation.
What they found is that it is very difficult to break down phytates in soybeans. In the study, the researchers boil the beans, pour off the water, soak them again, dehull them, steam them, drain them, and cool them. The phytic acid levels change very little with all of this effort.
It is only when they ferment the beans in the form of tempeh that the phytate levels reduce to about 45% of the levels of the soaked soybean. Fried tempeh is an improvement still, but if the tempeh is stored for two weeks at 5ºC and then fried, the researchers reached the optimal (but not perfect) reduction of the phytic acid. A 2003 study also found that the phytic acid level decreased by only 31% by fermenting soybeans.
Thus, fermentation is the only reasonable option for reducing phytates in soy. Keep these results in mind as you shop for soymilk and tofu. Soybeans in soymilk are soaked, strained, and cooked. Tofu has an additional step - a coagulant is added. Both of these products retain nearly 100% of the phytates. You will not get the mineral value out of them that you expect from the nutritional label. If you are an avid soymilk drinker, you might consider culturing it using a process similar to yogurt of kefir.