The Science of Solidifying – How Cheese and Tofu Solidify

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We eat a variety of foods. Among them, let’s take a look at some of the foods that are hardened, such as cheese, tofu, and konjac. Do you know the mechanism how they harden?

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Enzymatic Decomposition of Proteins

It is used to make cheese, such as leipajuusto.

What works here is an enzyme called chymosin, which is in rennet. Chymosin works on a protein called casein, which is in milk. Then, certain parts of the casein are cut off. This makes it difficult for the casein to dissolve in water, causing it to harden and produce cheese. For more information on how this process works, please click here.
Finnish Bread Cheese - Homemade Leipäjuusto
Leipäjuusto, Bread cheese served with cloudberry jam is a famous Finnish dish. You can make at home as long as you have access to rennet, an enzyme for cheese.

Cohesion Due to pH Change

It is used to make cottage cheese and other cheeses.

Casein is a protein. Proteins, and the amino acids from which proteins are made, change their solubility in water depending on pH. By adding acid to the milk, the casein in the milk is made less soluble in water. Cottage cheese is then made by solidifying that. For more information on how it works, please click here.
Cottage Cheese - Easy Homemade Cheese with Vinegar
Cottage cheese is a simple cheese that can be made by adding vinegar and lemon juice to milk. This article also mentions how cheese is made.

Cohesion by Salting Out

This is used in the production of tofu and konjac.

Tofu is solidified by heating soy milk and adding salt called Nigari to it. The protein in soy milk is in a stable state called colloid (hydrophilic colloid). In order to solidify it, the soy milk is first heated to denature the protein and make it easier to precipitate. Then, by adding Nigari, the colloid is made less soluble in water and precipitated.

This method of precipitating hydrophilic colloids by adding a large amount of electrolytes is called salting out.

The mechanism of konjac solidification is also based on colloidal salting out. Glucomannan, the main component of konjac, forms a hydrophilic colloid that dissolves well in water. Konjac is made by adding a strong basic coagulant to it.

Thermal Denaturation of Proteins

It is used to make egg tofu, chawanmushi, cheese, and tofu.

Heat changes the three-dimensional structure of proteins, making them irreversible. For example, when you boil an egg, it hardens, and when you cool it down, it does not return to a raw egg. This is called thermal denaturation of proteins. This heat denaturation is the main reason why egg tofu and chawanmushi harden. Cheese and tofu use other mechanisms as well, but I think heat denaturation makes them easier to solidify.
Cottage Cheese - Easy Homemade Cheese with Vinegar
Cottage cheese is a simple cheese that can be made by adding vinegar and lemon juice to milk. This article also mentions how cheese is made.
Ricotta Cheese - Homemade Cheese from Whey
Ricotta cheese is a cheese made from whey. Only a small amount of ricotta cheese can be made from whey. However, it has a great taste and texture.

Acid Denaturation of Proteins

This is used to make cottage cheese and ricotta cheese.

The acid changes the three-dimensional structure of the protein and makes it irreversible. This is called acid denaturation of proteins. I think protein cohesion is the main mechanism by which cottage cheese and ricotta cheese harden. However, this acid denaturation is probably also involved in some small way.
Cottage Cheese - Easy Homemade Cheese with Vinegar
Cottage cheese is a simple cheese that can be made by adding vinegar and lemon juice to milk. This article also mentions how cheese is made.
Ricotta Cheese - Homemade Cheese from Whey
Ricotta cheese is a cheese made from whey. Only a small amount of ricotta cheese can be made from whey. However, it has a great taste and texture.

Gelatin Gelation

This is used to make edamame tofu, jelly and so on.

Gelatin is made up of a network of proteins. When gelatin is placed in water and heated, the proteins in the gelatin loosen and move freely. To our eyes, the gelatin has dissolved in the hot water.

Gluing of Starch

This is used to make sesame tofu, peanuts tofu.

Starch is a substance made up of chains of glucose sugars that are tightly folded together. Normally, there is a strong hydrogen bond between these chains. Therefore, the chains do not come apart.

Categorize Food by Mechanism

We usually categorize dishes by their ingredients or how they are made. This time, I thought a little deeper and classified them by their mechanisms. When a dish does not turn out well, thinking about the mechanism in this way may help you solve the problem.

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