Fermentation makes food full of "magic", what kind of process is this?

Fermentation is nature's "magic". It is the process by which humans use microorganisms to create delicious food, giving the same food a variety of flavors.

For example, steamed buns, bread, yogurt, kimchi, bean paste, etc. are all delicious fermented foods. Regular consumption of fermented foods can also balance intestinal flora, maintain intestinal health, and regulate immunity.

So, how is food fermented? Let's explore the changes in fermented food.

Fermentation of pasta:

Different flours are needed to make different fermented pasta, and the flavors of the finished products are very different. For example, making bread requires flour ground from high-protein wheat, while making steamed buns only requires medium-gluten flour, and making cakes requires low-gluten flour.

Image source: Tuchong Creative

This is because flour with high protein content will produce better gluten after a long period of kneading, which can make the bread ferment better, have a unique flavor, and be soft, tough and chewy. However, steamed bread and cakes do not require high gluten.

The most commonly used ingredient for fermenting pasta is yeast. The reason why it can make food "expand" is because of the gas production of yeast.

When flour meets water, it breaks and starts to absorb water. When yeast comes into contact with starch, it starts to "work". It relies on the sugar in the flour and the added sugar to start metabolizing. This process produces energy, carbon dioxide gas and alcohol, which can make the dough full of bubbles and the structure soft.

Temperature has a great influence on the gas production of yeast. Generally, the yeast produces gas fastest at around 35°C. However, if the temperature is maintained at this level, more acid will be produced, affecting the taste. Therefore, it is generally recommended to maintain the temperature at 27°C for a better yeast flavor.

In addition to yeast, some people are accustomed to using baking soda as a leavening agent for pasta, but the flavor and color are not as good as those produced by yeast. If the mixture is uneven or the baking soda is not completely dissolved, the color of the food will turn brown in some parts and the taste will be bitter.

Compared with ordinary pasta, fermented pasta is soft and easy to digest, and is more friendly to people with poor stomachs and the elderly.

Fermentation of soybeans:

Soybeans themselves have a unique smell, and the flavors of fermented soybeans vary greatly. Common ones include natto, fermented tofu, and miso and soy sauce that can be used for seasoning.

Their unique flavors all come from microorganisms. For example, mold plays a major role in making bean paste. When making bean paste in the traditional way, you must first make koji, that is, cultivate a raw material that is a mixture of food and mycelium.

Then all the raw materials are immersed in brine. During this process, mold cannot grow and secretes various enzymes, including protease, amylase and cellulase. Protease breaks down the protein in the raw materials into polypeptides and amino acids; amylase converts starch into glucose, disaccharides, trisaccharides and dextrin; cellulase breaks down pectin, cellulose, hemicellulose and other raw materials into various sugars. This series of processes brings a unique flavor.

Soy sauce was originally the residual juice when making bean paste, also known as bean paste clear. Today's soy sauce is mainly made of defatted soybean meal and wheat bran, which are steamed and fermented with Aspergillus oryzae, and then poured with salt water. During the fermentation process, proteins are broken down into amino acids; starch is broken down into monosaccharides, disaccharides and polysaccharides. Amino acids react with sugars to appear brown.

Miso is a soybean paste unique to Japan. The brewing process requires cooking millet or rice first, and then placing it in a shallow dish to ferment and make koji. The prepared koji is put into crushed and cooked soybeans, and 5% to 15% salt and a portion of previously brewed miso are added. It is placed in an environment of 30 to 38 degrees Celsius. The lactic acid bacteria and salt-tolerant yeast in it will decompose the protein, carbohydrates and oil in the raw materials, generate flavor substances and undergo browning reactions. It takes several months to several years until the taste is mellow.

Natto is also made from fermented soybeans. After the soybeans are cooked, they are fermented with Bacillus subtilis natto at 40°C for 20 hours. The protein is broken down into amino acids by bacterial enzymes, and oligosaccharides are broken down into monosaccharides, producing a mixture of aromatic compounds with creamy and nutty flavors, as well as long-chain glutamic acid components and sucrose with long-chain branches (these two components make natto sticky and stringy).

The fermented tofu that people often eat is a food made from tofu fermented by molds, such as Actinobacillus and Mucor.

Although fermented soy products have a unique flavor, they generally contain high salt and should not be eaten too much.

Fermentation of vegetables

After fermentation, vegetables can be made into delicious foods such as pickles, sauerkraut, and kimchi. The main fermentation microorganisms are lactic acid bacteria, which are also the source of their special flavor.

To make pickles, the vegetables need to be completely immersed in salt water and sealed. Unrefined sea salt is often used to make the pickles taste crisper. This is because unrefined sea salt contains calcium, magnesium and other ingredients that can promote cross-linking and strengthen cell wall pectin. Next, the vegetables are placed in anoxic conditions, which inhibits the fermentation of yeast and mold. Only anaerobic bacteria such as lactic acid bacteria can continue to reproduce, consuming the sugars that have been metabolized in the vegetables, producing a variety of lactic acid, other acids, carbon dioxide and alcohol, and can also degrade the nitrite content in the pickles.

When kimchi is fermenting, low temperature and low salt are conducive to the growth of Leuconostoc mesenteroides, which can produce a light taste containing acid, alcohol, aromatic compounds, etc.; higher temperatures are conducive to the growth of Lactobacillus germinatus, which produces lactic acid. Generally, kimchi is mainly composed of Leuconostoc in the early stage, and then Lactobacillus is the main component.

The content of B vitamins will increase during the fermentation process of vegetables, but like fermented soy products, fermented vegetables generally contain high salt content, so the amount consumed needs to be controlled.

Fermentation of milk

Milk is a good source of calcium in the diet, but many people do not like the taste of milk. Instead, they prefer yogurt and cheese made from fermented milk.

The main microorganisms in fermenting yogurt are lactic acid bacteria (further simplified to two basic species: Lactobacillus bulgaricus and Streptococcus thermophilus). These two bacteria stimulate each other's growth, digest the lactose unique to milk, and produce lactic acid bacteria that are released into the milk. At the beginning, streptococci are more active, and later as the acidity increases, another bacteria becomes active. This process hinders the growth and reproduction of other microorganisms and allows casein to aggregate into semi-solid curds, making the originally liquid milk thicker.

Cheese is a dairy concentrate made by adding appropriate amounts of lactic acid bacteria starter, rennet and salt to sterilized milk to coagulate the casein in the milk and remove the whey. It not only has a rich taste, but also has further concentrated nutrition.

Studies have found that the beneficial bacteria in fermented dairy products can improve the intestinal microecological environment and regulate the body's immune mechanism.

However, when choosing yogurt and cheese, it is recommended that: for yogurt, choose sugar-free yogurt with a lactic acid bacteria count ≥ 106 CFU/g (mL) that has not been heat-treated after fermentation; for cheese, it is recommended to choose low-salt cheese.

Summarize:

The unique flavor of fermented foods is due to the magic of microorganisms. Although they taste delicious, it is not recommended to make fermented foods at home if you have no experience, in order to avoid the growth of bacteria and health hazards caused by poor control of the fermentation environment.

References:

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[8] Harold Mackey, author. Translated by Lin Huizhen. Food and Cooking. Milk, Eggs, Meat, Fish. Beijing Fine Arts Photography Publishing House. 2013.8

The article is produced by Science Popularization China-Starry Sky Project (Creation and Cultivation). Please indicate the source when reprinting.

Author: Xue Qingxin, one of the first nutrition instructors of the National Health Commission and a registered dietitian in China

Reviewer: Zhang Na, associate researcher and doctoral supervisor at the School of Public Health, Peking University