Coagulant: The magic Ingredient for Tofu

DATE: October 9th, 2020 Location: Berlin, Germany

Article: Eva Steinhorst

One of the most mysterious characteristics of Tofu is it’s consistency. What is it exactly, that defines whether tofu will be elastic or silky? In order to understand that, we first need to solve another puzzle, and that is to get behind the magic that transforms soymilk into Tofu. The answer is simple. All it takes is some coagulant. This is also why Tofu has actually originated as an accidental creation. With coagulants being natural products occurring for example in seawater or salt lakes, one can imagine how they were once somehow mixed in with soymilk, creating tofu. 

Many of you will already be puzzled by the term coagulant. However, one does not need a chemistry degree to understand what coagulant actually is and what process it unleashes. Coagulants are chemicals that cause particles dispersed in water to clump together, isolating solids from water. This process is also referred to as coagulation. The chemical process behind water coagulation is as follows: when coagulants are added to a mixture, the negative electric charge of particles are neutralized as coagulants are made up of positively charged molecules. Before, the negative charges of the molecules dispersed in the water were the force keeping them apart. Thanks to the koagulant, we can then extract the silky tofu texture from the water and put it in a box for pressing. 

Now we have already solved the first part of the puzzle, and that is the step between soymilk and tofu. Yet, many of you might wonder how it is possible that some of the tofu out there could be mistaken for custard, while the kind of tofu one would add to a stirfry appears a lot more solid. Here, the mysterious force at work is the kind of coagulant used. Overall, there are two different types of coagulants that are commonly used for making Tofu. The most popular coagulant is salt coagulant of which there are again two different kinds: Magnesium Chloride and Calcium Sulphate. The benefit of Magnesium Chloride (Nigari) is that the Tofu made with it contains less water. Thus, the result will be a tofu that is a lot firmer. Meanwhile, with Calcium Sulphate, there is usually more water, resulting in a smooth, tender texture. Thus, almost all silky tofu on the market is made with Calcium Sulphate. Yet, many tofu brands use both coagulants together in order to optimize the taste and the texture. Not only do these coagulants provide for taste and form, they also have numerous nutritional benefits, which is why they can be purchased as dietary supplements in many stores. 

Another coagulant that can transform soymilk into tofu are edible acids, for example citric acids or vinegar. However, since the coagulant does not only determine the consistency, but also the taste of the tofu, using acids will most likely result in a very sour taste. Salt coagulants on the other hand deliver a tofu that is much sweeter in taste. Overall, tofu produced with salt coagulants is smoother and more elastic, with pores, while the tofu made with acid does not have any pores and is a lot more solid. It’s texture can be compared to that of feta cheese. 

All in all, it can be said that tofu is not only defined by the soybeans used and their grinding process, but also by the coagulant of your choice. The picture below shows the difference again: the tofu on the top is silky tofu and the tofu at the bottom is firm tofu.