Fat meat grows in the old vinegar jar and can still be eaten, so what on earth is it?

Not long ago, a popular online video attracted the editor-Gufa vinegar workshop to grow something like fat in the vinegar jar. Uncle vinegar tore off a piece and tasted it.

However, it was not clear what it was in the last video, only mentioned that a chemistry teacher said it was "the crystallization of fat", but how could there be so much fat in the vinegar jar? what on earth is this?

Opinions vary in the comment area, and there is no reliable explanation, but it provides some clues. So the editor decided to do a "popular online video identification" by himself.

After checking the data, I found that "growing meat in vinegar" is not an anecdote, but it is common in vinegar workshops in Shaanxi and Shanxi. They call this piece of meat in vinegar "vinegar treasure" and "vinegar moth", and make special snacks similar to cold noodles and cold skins.

The ancient agronomic book Qi Min Yao Shu also had a record: ". Yi Sheng, stop do not move, scratch and stir it, tens of days vinegar into heavy ", in which" clothing "refers to vinegar treasure. In foreign countries, it is known as "mother of vinegar".

Many netizens also found similar foreign bodies growing in their vinegar and asked questions online curiously:

Screenshot from www.douban.com

Like the netizen above, seeing this piece of meat, many people think of the "meat Ganoderma lucidum" introduced in CCTV's "approaching Science" column, also known as too old, which occasionally appears in ponds and swamps.

Taizao is essentially a colony of slime molds, bacteria and fungi, as well as their metabolites, which are not recommended for food or medicine because of their complex ingredients.

Although it looks like a "familiar recipe", vinegar Bao looks much more "simple" and more like jelly.

But the answer is close. Vinegar Bao is a bacterial membrane made up of bacteria and their metabolites. Is it vinegar contaminated by bacteria? how can you still eat it?

These bacteria are not harmful miscellaneous bacteria, they are called "acetic acid bacteria" and are very useful "tool bacteria" for human beings. Without them, vinegar could not be brewed at all. After all, not all kinds of bacteria can stand such a sour environment.

Just like lactic acid bacteria fermented yogurt, acetic acid bacteria are the core backbone of vinegar production. Sugars in grains or fruits are fermented into alcohol, and acetic acid bacteria can oxidize alcohol (ethanol) into acetic acid (acetic acid), which is the basic component of vinegar.

Acetic acid bacteria not only do the main business of making vinegar, but also do some sideline-metabolism to produce polysaccharide by-products. They consume nutrients such as glucose and fructose in vinegar jars and convert them into polysaccharides (made up of many monosaccharide molecules).

Some of these polysaccharides are soluble in vinegar and some are insoluble. Insoluble polysaccharides, such as bacterial cellulose, adhere to the cell wall of acetic acid bacteria and form layers of reticulated bacterial membranes as the cells divide and proliferate.

Wei ran, wait. Film production mechanism of acetic acid bacteria and effect of membrane on fermentation quality of vinegar [J]. Food and fermentation Industry, 2014)

When the bacterial membrane reaches a certain weight, it sinks, forms a new film on it, and finally accumulates into distinct pieces of "meat".

There are two kinds of bacterial membranes: one is homopolysaccharide composed of the same monosaccharide molecules, such as bacterial cellulose and glucan composed of multiple glucose molecules, fructose composed of multiple fructose molecules, and hybrid polysaccharides composed of 2-8 monosaccharide molecules.

The membrane characteristics produced by different acetic acid bacteria are also different. For example, the common Acetobacter Acetobacter (Acetobacter aceti) forms a loose membrane, like fat meat, while a woody Acetobacter (Komagataeibacter xylinus) forms a dense membrane, like jelly.

Then why is it that the vinegar bought in the market has been kept for a long time, and there is no bacterial film produced?

Bacterial membranes are not produced in all vinegar. On the one hand, it depends on the strain of acetic acid bacteria, on the other hand, it also depends on the environmental conditions of culture.

Scientists found that some acetic acid bacteria formed colonies with smooth surfaces and some rough surfaces, so they were divided into S bacteria and R bacteria (corresponding to "smooth" and "rough"). The former will not form a bacterial membrane, but the latter will.

Both types of bacteria can secrete polysaccharides, but R bacteria can produce insoluble polysaccharides, and in the static culture medium, the polysaccharide yield of R bacteria is more than 6 times that of S bacteria, which is enough to accumulate into a membrane.

Some acetic acid bacteria, which originally did not produce bacterial membrane, may also mutate into "membrane force" in the process of fermentation from generation to generation, and become a "membrane mage" from an early age.

"A skilful wife cannot make bricks without rice". In order for acetic acid bacteria to exert their "membrane power", they need to provide them with favorite sweets, including sucrose, glucose, fructose and other easily digestible sugars. The researchers found that the surface of fruit vinegar such as astringent persimmon vinegar and apricot vinegar is very easy to grow bacterial film. Adding appropriate amount of organic acids (such as malic acid, lactic acid), ethanol (alcohol), and peptone can also promote the growth of bacterial membrane.

When the culture medium is in place, suitable conditions are needed: a warm environment of 28 ℃ to 30 ℃, acidic pH of 4 to 7, and plenty of oxygen. If there is too much acetic acid and the acidity of the culture medium is too high, it will inhibit the growth of bacterial membrane.

However, even if the vinegar you buy meets these brewing conditions, it may not form a bacterial membrane. Because industrial vinegar is pasteurized before leaving the factory for food safety, killing bacteria, including acetic acid bacteria.

On the other hand, the vinegar produced by folk workshops or home-brewed vinegar is generally used to produce bacterial membrane after buying it back home. These vinegar may also contain live bacteria and unfermented sugars, and if the environment is just right, acetic acid bacteria will start to use the "membrane method" to make trouble.

The membrane itself can be eaten and will not contaminate vinegar (if you are not sure whether it is a pollutant, it is not recommended).

Vinegar brewing industry loves and hates bacterial membranes. On the one hand, acetic acid bacteria aggregate into bacterial membrane, which has great unity and inhibits the growth of other miscellaneous bacteria; gluconic acid and other by-products are also produced in the process of producing bacterial membrane to improve the flavor of vinegar. On the other hand, acetic acid and polysaccharides can not be both, acetic acid bacteria production membrane will consume more sugar (carbon source) and protein (nitrogen source), so that the production of acetic acid is reduced.

But the acetic acid bacteria membrane is a good thing for the entire food industry, and it has long been integrated into our daily diet.

People most often eat coconut, yes, coconut is not coconut pulp, but wood acetic acid bacteria fermented coconut milk to form a bacterial cellulose membrane.

Coloring the bacterial cellulose film with Monascus can also be imitated into meat or seafood, that is, "vegetarian meat" like konjac.

A beverage called "black tea bacteria" (also known as "kombucha") also produces bacterial membranes, which contain acetic acid bacteria (mainly woody acetic acid bacteria), yeasts, lactic acid bacteria and their metabolites, mainly bacterial cellulose.

Bacterial cellulose and plant cellulose can not be dig