Tofu with Adjusted Soy Milk – 2 The Mechanism of Tofu

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In fact, we learned that there is not much difference in soybean solids and protein content, and that different products contain stabilizers and pH adjusters.

Now in this article, I will explain how tofu is made from soy milk.

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Isn’t Tofu a Colloidal Salting Out?

Actually, it seems that tofu is not colloidal salting out. You may be thinking, “What?” but tofu is colloidal salt precipitation, a standard subject in high school chemistry.

In soy milk, a lot of proteins come together to form a colloid. Then, when bittern is added, salt precipitation occurs and tofu is formed. This is what is written in high school textbooks and reference books.

However, if you read the papers on how tofu is made, you will find that the actual reaction is much more complicated.

How Tofu is Made

In this section, I will explain the mechanism of tofu making in detail based on the paper. If you find it too complicated, you can skip it and go on to the next article.
Tofu with Adjusted Soy Milk - 3 Sodifying Experiments
Are you interested in homemade tofu? Is it possible to make tofu using store-bought soy milk outside of Japan? I searched it and did trials.

First, let me quote and translate key sentences about how tofu is made.

Quote and Translate

Soybean milk is considered to be an emulsified dispersion composed mainly of oil bodies (oil body-like particles), particle proteins, and soluble proteins, which are partially bound to the surface of 11S and 7S proteins.
(Omitted)
When a coagulant is added to soybean milk, the formation of tofu begins with the binding of particle proteins to oil droplets, followed by the further binding of soluble proteins.

https://core.ac.uk/download/pdf/144248469.pdf

This is how tofu is made. I think this is not clear enough, so I will explain it step by step based on the contents of this paper.

Soy Milk Before Heating

The first thing to know is that soy milk is not a simple colloidal solution of proteins. It contains oil droplets and proteins in what is related to tofu making.

Before heating, soy milk contains proteins dissolved in water as they are (soluble proteins) and proteins surrounded by oil droplets (protein-bound oil droplets).

Soy Milk After Heating

When soy milk is heated, the bonds between the oil droplets and the protein particles are broken, and the protein particles form on their own (particle proteins). In other words, heated soymilk contains three types of particles: protein dissolved in water, protein particles, and oil droplets (oil body).

How Bittern Works

What happens when you add bittern to soy milk after it is heated?

As explained on the cottage cheese page, the solubility drops because the charge on the protein is reduced to zero. The protein recombines with the oil droplets. Proteins that are initially soluble in water as soluble proteins also lose their solubility and bind to oil droplets. The result of these particles bonding with each other is the jelly mass that is the basis of tofu.

Types of Tofu

When served in this jelly state, it is called Oboro-Tofu or Yose-Tofu. However, as the name “Oboro-Tofu” implies, it is quite soft. This is due to the large amount of water that is held in the particles as they bond together. Momen-Tofu, firm tofu is made by crumbling this tofu, packing it in a box, and applying pressure to harden it. In Kinugoshi-Tofu, silk tofu, soy milk and coagulant are placed in a container and allowed to set.

Experiments on Solidifying Soy Milk

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