Many winemakers are aware of a situation where a film formed on the surface of the drink due to air entering the vessel. This process completely spoils the taste and properties of wine, making it unsuitable for consumption, and it is provoked by bacteria of acetic acid fermentation. By themselves, such microorganisms are not dangerous and are always found in wine and beer, they begin to cause harm only in contact with air.
But today this, it would seem, not a very good property is used for the benefit of mankind in certain industries.
What are bacteria
The most striking example of the work of acetic acid bacteria is the souring of low alcohol wine. This phenomenon was known in antiquity, but a scientific explanation of the process was given only in the 60s of the century before last by the French microbiologist Louis Pasteur. It was he who discovered the causative agents of the appearance of a cloudy film on the surface of the wine, which causes its souring, in other words, the transformation into vinegar.
This is characteristic of low-alcohol drinks left in incomplete open vessels with free access to air. Upon further study, it turned out that the “vinegar mushroom” discovered by the chemist actually represents a whole species of various bacteria.
The ability of microorganisms
Acetic acid bacteria are actually involved in the processes of not only souring wine. They are able to oxidize alcohols such as ethyl, propyl and butyl, forming acetic, propionic and butyric acids from them, respectively. That is, any drink with the content of such alcohol can be spoiled due to the vital activity of bacteria. Do not be afraid only for liquids containing methyl and higher alcohols, since they form a product toxic to microorganisms during oxidation.
Process features
The oxidation of alcohols under the influence of acetic acid bacteria is a dehydrogenation. The whole process can be expressed in the chemical formula, where ethanol is initially taken, which is converted under the influence of oxygen into acetic acid, water and the released energy:
CH 3 CH 2 OH + O 2 = CH 3 COOH + H 2 O + energy
If there is too much alcohol in the environment, then the result of the process will be the formation of only acid and a minimum energy release, which is not enough for further bacterial activity. That is why they have to oxidize as much alcohol as possible, which brings oxidation closer to other anaerobic processes, but leaves it individual according to certain characteristics.
Features
A distinctive feature of the action of acetic acid bacteria is always the formation of a film on the surface of the substrate.
The work of acetic acid bacteria and their properties depend on the variety of microorganisms and can change color, thickness, strength and other characteristics. To date, a huge number of species of these typical aerobes have already been discovered. All of them are able to multiply very quickly, especially when added to the initial liquid finished acetic acid, which accelerates the process of obtaining vinegar in production. In life, acetic acid bacteria are found in air, soil, any fermentation product, on the surface of berries and fruits, water and so on.
External description
Under ideal conditions, cells are short sticks and do not form spores. Depending on age, habitat and many secondary reasons, the shape and size of microorganisms can vary. Adverse conditions provoke cells to grow and sometimes become covered with mucus. In large quantities, they form mucus clusters.
Temperature has a special effect on the vital functions of cells. If its indicator is below 15 degrees, then the reproduction will be slowed down, and outwardly the bacteria will be short and thick sticks. At a rate of up to 34 degrees, the environment is considered ideal, and the cells feel good. With an increase, the formation of various deformities in the form is possible.
Beneficial features
In addition to the fact that the vital activity of bacteria harms winemaking, there are a number of examples of the successful use by humans of the characteristics of microorganisms.
So, the main role is played by acetic acid bacteria in the production and manufacture of table vinegar from wine or diluted alcohol. It is carried out to this day in two ways.
The first is a slower but more thorough process, called Orleans or just French. For him, it is necessary to prepare wine, previously acidified or diluted with water. Place it in prepared flat containers so that the contact surface with air is maximum, and release particles of the previously formed Acetobacter orleanense film into the liquid. It has a yellow color and a strong texture that allows you to maintain the transparency of the liquid under it.
After fermentation, part of the substrate is carefully taken from the tank and replaced with a similar amount of diluted wine, after which the process resumes.
The second method is faster and is applicable for the oxidation of diluted alcohol. To do this, it is passed through special containers with beech chips, in order to also increase the adhesion surface with bacteria. The containers are necessarily equipped with false bottoms with the ability to pass air through them. Thus, the alcohol sprayed by the air flows settles on the chips and oxidizes, after which it is taken from the bottom of the vessel, and a new substrate is added from above.
In addition, cells are used for:
- soaking apples with yeast;
- ascorbic acid production;
- growing Kombucha;
- making kefir.
In general, in the production of absolutely all lactic acid products, parallel fermentation is observed, that is, lactic acid and acetic acid bacteria together provide the appearance of milk processing products in the form we are used to.
Negative properties
Despite this positive value, acetic acid bacteria suggest a danger to certain industries. So, in winemaking, microorganisms are considered pathogenic, since they can provoke the fermentation process, despite the fact that they are almost always found in beer and wine. To deactivate them, carefully stop the drinks from contact with air, because it is he who provokes the onset of fermentation. Acetic acid obtained from souring wine is always collected at the bottom, from where it can be collected, but the taste and aroma of the remaining drink will be spoiled forever.
If you ignore the process that has begun, then the entire contents of the container can turn into ordinary wine vinegar.
Similarly, bacteria can cause acidification of salted or pickled vegetables.