All About Tofu - Part I

The versatile little soy bean is used to make such delicious foods as tofu, tempeh, miso, and soy milk, and yet it's misunderstood, especially here in the West. Tofu is derided, scoffed at, and even feared by some, and I'm here to set things right. Our little lesson may seem technical at first, but once you read it, I think you'll come away with a much better understanding of our high-protein friend and look with suspicion upon anyone who denigrates it. I think you'll also gain a new perspective of animal-based cheese, which far too many people think "they couldn't live without." When we look closer at its production, perhaps you just might change your mind.

Tofu originated in China about 2000 years ago, and while the details of its discovery are uncertain, legend has it that it was discovered by accident when a Chinese cook added the seaweed nigari to a pot of soybean milk, causing it to curdle, and the result was tofu.

Tofu was introduced into Japan in the 8th century, where it was originally known as "okabe," but was not called "tofu" until the 15th century, though tofu did not gain its great widespread popularity in Japan until the 17th century.

Tofu's popularity in the West has mirrored the increasing interest in healthier foods. First gaining more widespread attention during the 1960s, tofu has been skyrocketing in popularity ever since research has begun to reveal the many significant benefits of this food.
So, what is tofu? What is this white block of what is also called "bean curd"?

Tofu or Dofu (based on the Chinese spelling) is a food that is made in much the same way that people make dairy-based cheese. First, you coagulate soy milk.

Well, let's back up. As with cheese, when you make tofu, the first you need to start with is milk.

In the case of dairy-based cheese, in our crazy world, we use the milk of animals. To make tofu, we use soy milk. Now, most commercial tofu makers make their own soy milk, which anyone can do by soaking, grinding, boiling, and straining dried (or, less commonly, fresh) soybeans.

When you have your soy milk, you then need to add a coagulant. When you coagulate something, you cause it to curdle. In other words, you transform it from a liquid into a soft semisolid or solid mass. Most of us have seen curdling when cow’s milk starts to go bad and you see little semi-solid white lumps floating around. Those are curds. That’s a process of curdling to indicate that it’s spoiling, that it’s going sour.

But there are other ways to sour milk intentionally. You do this by adding an agent that will produce that souring effect. Acidic liquid substances are the most obvious, such as vinegar or lemon juice. For instance, and I talk about this in my new baking cookbook, to make “buttermilk,” all you need to do is add some lemon juice or vinegar to your non-dairy milk, and you’ve got what is sour milk – “i.e. buttermilk.”

So that you better understand the process of creating tofu, let me first talk a little about curdling cow’s milk before I continue with soy milk. For animal-based cheese, what is most often used as a curdling agent is rennet. Rennet is essentially a bunch of enzymes produced in the stomach of mammals to help the offspring digest the mother's milk. One of the enzymes causes the milk to coagulate, to curdle or separate into solids (curds) and liquid (whey). Now you understand what Little Miss Muffet was eating. Couldn’t tell ya why she’d wanna eat it, but now at least you know what it is: curds and whey are the solid and liquid results of curdled milk.

For cow’s milk cheese, the rennet is extracted from the fourth stomach of young calves. And where would you find an abundance of young calf stomachs? The veal industry, of course. The stomachs used to get rennet are a by-product of veal production. Each ruminant animal produces the special kind of rennet needed to digest that species' mother's milk, so there is kid-goat rennet especially for goat’s milk cheese and lamb-rennet for sheep’s-milk cheese.

Let's pause for a moment to examine a few health considerataions. I mentioned that increased acidity in cow’s milk causes curdling. Let’s go a little deeper. What’s actually happening is that the milk proteins (the casein) is tangling up into solid masses or "curds.” The rest, which contains only whey proteins, is the whey. In cow's milk, 80%-87% of the proteins are caseins.

If you haven’t yet read T. Colin Campbell’s The China Study, I can’t recommend it highly enough. I urge you to read it. Campbell is a highly respected researcher and policy advisor in the field of diet and cancer. He is Professor Emeritus of Nutritional Biochemistry at Cornell University and has had a long career in research, teaching and development of national/international studies on diet, nutrition and health.

About casein he says that it is the “#1 carcinogen (i.e. cancer-causing substance) that people come in contact with on a daily basis.” We’re consuming, drinking, swallowing, digesting this stuff every time we drink animal milk or eat animal-based cheese. And in cheese it’s even worse, because the casein is super concentrated.

So back to rennet, there is vegetarian rennet, and sometimes it’s used in the production of kosher cheeses but just keep in mind that though rennet can be produced by plants that have coagulating properties (such as nettles, thistles, or mallow – as in marshmallow – you probably know that marshmallows that are made with gelatin (the boiled hooves, bones, and other leftover body parts of the slaughter industry), but they used to be made with the marshmallow plant!).

Though plant-based rennet is technically possible to create, nearly all “vegetarian” kosher cheeses are produced with either microbial rennet or genetically modified rennet. Microbial rennet is produced by using certain molds that are fermented. Apparently, using microbial rennet produces a slightly bitter tasting cheese, so with the development of genetic engineering, scientists starting using calf genes to modify some bacteria, fungus or yeast to make them produce Chymosin, one of the enzymes found in rennet. Chymosin produced by genetically modified organisms was the first artificially produced enzyme to be registered and allowed by the FDA in the USA. In 1999, about 60% of U.S. hard cheese was made with genetically engineered Chymosin.

When we eat animal-based cheese, we're consuming either the by-products of the veal industry or genetically engineered enzymes based on calf genes.

So that’s rennet – used to curdle animal milk to make animal-based cheese. Now we can return to tofu.

As I said, you have to add a coagulant to your soy milk to curdle it, and for commercial tofu, the two coagulant types most commonly added are acid-based and salt-based.

SALT COAGULANTS

-An example of a salt-based coagulant is calcium sulfate, which is essentially tasteless. Tofu that’s made with calcium sulfate is obviously rich in calcium, and such tofu is pretty common. Tofu made with calcium sulfate tends to be Chinese-style tofu, which is tender but slightly brittle in texture.

-Other salt coagulants used are Chloride-type Nigari salts - Magnesium chloride and calcium chloride. These are the coagulants used to make Japanese-style tofu with a smooth and tender texture. Calcium chloride is a common coagulant for tofu in North America. You’ll recognize this coagulant on the list of ingredients, because it will most likely say Nigari, which consists primarily of magnesium chloride. It’s produced from seawater after the sodium chloride is removed and the water evaporated.

ACID COAGULANTS

Another coagulant that’s used – mostly for silken tofu or soft – is Glucono delta-lactone (GDL), a naturally occurring organic acid, which produces a very fine textured tofu that is almost jelly-like. Think silken tofu.

Tofu producers may choose to use one or more of these coagulants, as they each play a role in producing a desired texture in the finished tofu. So when you notice a different taste or texture in tofu depending on the brand, this is why. A lot of it depends on the coagulant used. The coagulant mixture is dissolved into water, and the solution is then stirred into boiled soy milk until the mixture curdles.

So, now you’ve got your curds, which, like in the process of making cheese, you press these curds. The curds are processed differently depending on the form of tofu that is being made. For soft silken tofu, the soy milk is curdled directly in the tofu's selling package. For standard firm Asian tofu, the soy curd is cut and strained of excess liquid using cheese cloth or muslin and then lightly pressed to produce a soft cake. Firmer tofus are further pressed to remove even more liquid.

In Part II, we'll talk about the various texture varieties of tofu. That's it. Science lesson over.

(Visit CompassionateCooks.com for tofu recipes or for our DVD, in which we demonstrate various uses with tofu, such as our Veggie Stir-Fry with Peanut Sauce and Eggless Egg Salad.)