Lately I've been preoccupied with making tofu. So far I've gone through maybe 2 pounds of dried soybeans and countless cups of soybean milk in this pursuit. Thanks to my Soyquick soymilk machine I can quickly make rough, "country-style" tofu that's satisfying, and unlike store-bought tofu, actually tastes like the beans. But unlike store-bought tofu, it has a weird airy texture I'm not quite sure I like.
I suspect the weird texture has something to do with the coagulent I'm using, as using different coagulents, in different combinations and quantities can yield curds of different qualities. (If you don't know, traditional tofu making involves several steps. Soybeans are soaked, crushed, and cooked into a soymilk before a coagulant added. The cooking denatures the proteins so that the coagulent can pull them out of solution, forming proteins clumps, aka, curds. These curds are pressed together into blocks of tofu.)
Historically, tofu coagulents were either a combination of magnesium chloride and magnesium sulfate extracted from seawater (nigari) or mined calcium sulfate (gypsum). But a third substance, Glucono delta-lactone (GDL) is now used to manufacture silken tofu. It's this GDL that was the focus of my little experiment.
For the uninitiated, from this point on the post may contain way more info than you really want to know about this particular coagulant, but due to the thinness of information on the internets on this topic i feel it necessary to create this post as a service to those who really need to or want to know.
I've been using nigari from Rainbow Grocery, which results in the aforementioned airy tofu. What I really want is a silken tofu, something with a creamy, custard-like texture, and GDL is the coagulent of choice for such a job. But I didn't know how much to use or really how to use it at all, since the instructions on the package were completely useless. Following the cursed instructions on the packet of GDL resulted in tiny, runny curds that fell apart at the touch of a spoon. I had to develop my own recipe.
Doing some research on the internets provided a clearer understanding of the substance, revealing that GDL coagulates soymilk by lowering its pH. According to one source, about half the protein of soy is soluble at neutral pH but insoluble in acid conditions. In contact with water, GDL hydrolizes into gluconic acid, causing the proteins in the milk to precipitate. Moreover, hydrolysis of GDL is accelerated at higher temperatures. Which made sense since I had read that commercial production of silky tofu packaged in plastic tubs involved mixing GDL into the containers at room temperature and then heating them up in waterbaths. So that's the model I used for my experiment.
Since I wanted to know how much GDL to use, I filled 5 glass bottles with fractions of a teaspoon of it. 1/4th, 1/8th, 1/16th, 1/32th, and 1/64th of a teaspoon. Each vial was filled with 8-1/4 tsp. of thick soymilk (two Soyquick cups of dry soybeans and the minimum level of water in the Soyquick jug). As a side experiment I wanted to know if the concentration of soymilk had anything to do with how well it coagulated, so I replicated the experiment using extra-thick soymilk (the thick soymilk reduced to half its original volume). I then stuck them all in a waterbath for 15 minutes. The water temperature inside the inner container reached something like 150 degrees F.
Here are the results, core samples of the vials (via an apple corer!) from highest concentration of GDL to lowest (top to bottom).
As you can see, 1/64th of a tsp is way too little GDL. At 1/4 tsp (the top sample), the resulting tofu was eerily firm, and sour tasting to boot. 1/8th and 1/16th tsp. specimens were still too firm for my taste, at 1/32th of a tsp. the flavor and texture was the best. As for the side experiment with the thicker soymilk, I report that all of the vials failed to gel, producing no tofu at all. The next morning I worked out the math and arrived at this recipe: 1-1/4 cup + 2 tbsp. thick country style soymilk to 1/4 tsp. GDL. I put everything into my two-cup Pyrex measuring cup, put that in a waterbath with a temperature probe in the mixture and heated it up to 190 degrees F. Yes, the temp of the test tubes were way less, but it didn't seem to matter, because
Eureka! Creamy, custardy tofu!!
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