Napoleon III in 1863 asked a scientist Louis Pasteur to find out why such an enormous amount of wine spoils in transit, not having arrived at the destination, thus making a tremendous financial harm. Pasteur had engaged in wine researches and did the known discovery that contact with oxygen turns wine sour, because the number of harmful bacteria increases greatly. This discovery was called the fermentation process. It was also discovered that a small amount of oxygen is quite necessary for wine maturing, and that oxygen must influence wine gradually, in very small doses. Pasteur formulated a principle, that there has to be as much oxygen in a bottle of wine, as is necessary for the process of wine maturing. Actually oxygen accelerates wine maturing much, but only if there is a small amount of it. If there is too much air in a bottle, wine begins to spoil.

Louis Pasteur also found out, that the fermentation process is caused by lower organisms - unicellular microfungi which got the name yeast fungi. The enormous accumulation of yeast fungi looks like a grey or a bit yellow mass, called the yeast. Although in 1809 chemist Becher discovered that an alcohol produces during the fermentation process of sweeteners, but, the fermentation process itself was first described and grounded by Louis Pasteur, creating the scientific basis for the winemaking. In 1866 he published his work "Wine researches". It appeared that the fermentation process can take place in very different sugary liquids, both natural and artificially made.

The fermentation process is a biochemical process as a result of which an alcohol and carbon dioxide are produced of invert sugars (glucose and fructose). The cause of an alcohol fermentation process is yeast. In a result of their vital functions sugar is processed into alcohol and carbon dioxide, which extracts as bubbles. An alcohol fermentation process passes a few stages. On the first stage wort becomes cloudy, foam appears. Then comes the stage of active fermentation process, the enormous cap of foam appears on the surface, and the last stage is afterfermentation. The sediment is seen, the amount of carbon dioxide diminishes, the product slightly lightens up.

Yeast is widespread in nature; in a dry state it easily transfers by means of wind, therefore the fermentation process takes place everywhere, where sugary liquids are present.

It gets into the grapes juice from the surface of vine berries. There is an enormously great number of yeasts and bacteria which mostly are harmful for the winemaking. The composition of wine changes for bad at development of lactic-acid and different mold bacteria etc. If there are any acetic-acid bacteria, wine goes sour and changes into vinegar.

The fermentation process can take place not in any terms, in fact for performing their vital functions different yeasts require certain terms. Many harmful for the winemaking yeasts and bacteria can not live without air, thus oxygen is necessary for their vital functions. Any winemaker needs to know this important circumstance. For a correct alcohol fermentation process you need an optimum temperature, presence of nutritives and absence of air access.

The correct temperature for the fermentation process. If it is too warm in the apartment, yeast for the fermentation process feels bad and scarcely propagates; the fermentation process then goes poorly, languidly, and even can stop. At high temperature it is also easy not only for alcohol to develop, but also for other, harmful yeast fungi. The temperature influences chemical composition of wine, the lower temperature is - the less volatile acids produce, the yield of alcohol increases, a high quality aroma preserves better. But too low temperatures slow the work of yeast down; the fermentation process in this case often stops. During the practice of the winemaking it was found, that the less harmful yeasts and bacteria there are in fermenting juice - the higher is the maximum possible temperature of the fermentation process, but it is better for it not to exceed 25°C.

The most favorable temperature for an alcohol fermentation process is 18-20°C. Thus a temperature in the room, where a fermentation process takes place, must be the same, equal in the day and night, without harsh and frequent changes. Any strong temperature drops slows down the fermentation process and yeast work.

Presence of nutrition for yeast fungi. Nutrition for yeast fungi generally is represented by albuminous (nitrous) and mineral matters, microelements, and just a bit of sugary matters. Among minerals the most important are phosphoric acid and potassium. Sugar for yeast is needed much less, and in the case of its lack yeast works even without sugar. All these matters usually are present in fruit juices, but if it is strongly water-diluted, the fermentation process will be much slower and will take place only for some time.

If there is a lack of nutritives in a fermenting environment, the fermentation process will flow languidly or will stop at all. In this case the fermentation process is often finished long before all the sugar can be processed by yeast into alcohol, therefore wine produces with small amount of alcohol content and afterwards can easily spoil - turn sour. At the fermentation process the transformation of sugars takes place according to the reproduction and growth of yeast cells. The factors of growth are vitamins, mineral matters, amino acids. The content of sugars in wort up to 20% does not slow down the fermentation process; the high concentrations of sugars stop the fermentation process.

Absence of air access. Oxygen plays an important role at the initial stage of fermentation, favors the propagation of yeast, but under the influence of oxygen yeast can oxidize ethyl alcohol. Under air access to fermenting wine there also can develop yeast and bacteria of other, harmful fermentations, and spoil the wine; therefore a wine fermentation process is conducted without access of air. For this purpose the vessel for the fermentation process is hermetically closed with a lid, and to let carbon gas, appearing at the fermentation process, quit they use a water bibb or put on a vessel a medical rubber glove with the pricked fingers. At the fermentation process the glove swells up, and after its end - falls off. A water bibb is an ordinary rubber or glass tube of small section, one end of which is hermetically fastened to the lid of the vessel for the fermentation process, and other is put in a vessel with water. Then at a fermentation process the bubbles of carbon dioxide easily go out through water which, in its turn prevents the penetration of air in a fermenting vessel.