Soy foods are widely used in China as an adjunct to animal foods. The Chinese have perfected numerous ways of fermenting soy in order to neutralize phytic acid (which blocks minerals like zinc and calcium), enzyme inhibitors (which block digestion) and goitrogens (which inhibit thyroid function.) Traditional preparation of soymilk begins with soaking until the beans become soft. The softened beans are ground into a mush on a stone grinder, using copious amounts of water. The mush is then put into a cloth bag and placed under a weight or heavy rock so that all the liquid is squeezed out. The resulting soy paste is then cooked in fresh water. Large amounts of dirty scum that rise to the surface are carefully removed. To serve, raw egg or dried shrimp are placed in a bowl along with scallions, soy sauce, flavorings and vinegar, and the scalding soy milk is poured over. The vinegar causes the soy milk to curdle slightly. In traditional times, homemade soymilk was consumed by the elderly and by nursing mothers in the belief that it stimulated breastmilk, but was not normally used in feeding infants.4
Industrial methods for the production of soymilk leave out the all-important squeezing and skimming steps. The presoaking is shortened by using an alkaline solution. This process helps deactivate some of the enzyme inhibitors, but not the other antinutrients. The high pH value of the soaking solution results in a decrease in cystine content when the beverage is heated, thus lowering total protein availability and soymilk's usefulness as a protein source.5 Various refined sweeteners, preservatives and stabilizers may then be added.
The real value of the soybean is that it can be made into soy sauce, the salty elixir that gives Oriental food its unique character. Traditional soy sauce is made by a fermentation process that takes six to eight months to complete. This long and careful procedure creates a mix of phenolic compounds, including a natural form of glutamic acid, that contribute to the unique taste and aroma of traditionally brewed soy sauce. The modern bioreactor method produces a product by rapid hydrolysis, rather than by complete fermentation, in the space of two days, and uses the enzyme glutamase as a reactor, so that the final product contains large amounts of the kind of unnatural glutamic acid that is found in MSG.6