Turning water into "milk" is a basic skill for chefs!

Can water be turned into "milk"? Of course it can. You may have drunk a lot of bone broth and fish broth that are milky white like milk. It is normal for colorless and transparent water to change during the stewing process. However, the ingredients that can be stewed to produce a milky white effect are very limited, and sometimes the same ingredients stewed into a clear soup. What's going on?

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What the soup looks like in the end depends not only on the ingredients in the soup, but also on the way these ingredients exist in relation to each other. Vegetable soup is unlikely to produce a milky white effect, because the ingredients dissolved in the soup are mainly salt and other seasonings, while a small amount of cooking oil is insoluble in water and floats directly on the surface to form circles of oil, while the soup itself remains basically colorless and transparent. It can be said that the inorganic salts, oils and water in the vegetable soup are almost independent of each other and do not affect each other.

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But broth is different. When meat is used to make broth, the fat content dissolved in the broth is higher, and during the long cooking time of the meat, the protein will be hydrolyzed to form free amino acids that enter the broth. Under normal circumstances, water and oil are immiscible, but when amino acids or soluble proteins are present, they can coexist harmoniously.

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Amino acids or soluble proteins are emulsifiers, also called surfactants. There must be hydrophilic groups and hydrophobic but lipophilic groups in its molecular structure. Depending on the strength of its hydrophilic and lipophilic abilities, it may grab oil molecules and make the oil evenly distributed in the water, or grab water molecules and make the water evenly distributed in the oil. Most of the soups we see when cooking are the former.

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In addition, egg yolk is also a typical emulsifier. The mayonnaise we usually eat is a typical water-in-oil emulsion. Oil-in-water emulsions are more common in skin care products, such as creams or ointments.

When the oil is wrapped by the emulsifier into small balls and evenly distributed in the water, the incident light is scattered, so the liquid is no longer transparent, but appears milky white, very similar to milk. We call this form of liquid an emulsion. Milk is a natural emulsion because it naturally contains a certain amount of milk fat and milk protein.

Generally speaking, making a white soup requires three basic conditions: enough fat, emulsifier, and mixing the emulsifier, fat, and water by stirring or other methods. Many people don't know how to make a milky white soup when making fish soup. The main reason may be that the fish they choose does not have enough fat, such as crucian carp. If you fry the fish in oil first to make up the fat, and then add water to cook, the soup will be milky white.

Fish soup may become clear soup | Pixabay

Transparent vegetable soup lacks not only fat but also emulsifiers. If you stir-fry vegetables and a little meat in advance and then add water to boil, it is possible to form a white soup.

The milky soup tastes good, but it is just a liquid with oil suspended in it. So if you like to drink it, it is best to just taste it. Drinking too much will make you fat.

Author: Tuan Xiaozhi

Editor: Zhang Shuaiyan

References

[1] Zhao Jinfu. Food Technology, 2nd Edition. China Light Industry Press. 2008

[2] Fan Zhihong. Is milky white soup really nutritious? New Rural Technology, 2018 (2): 56-56

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