Traditional winemaking uses the natural fermentation process. Natural fermentation means that the grapes are crushed and the yeasts carried by the grapes are spontaneously propagated in the grape pulp or separated grape juice without adding any artificial bacteria, and finally fermented into wine.
1. The effect of temperature on fermentation
Yeast can only survive at a certain temperature. When the temperature is lower than 10℃, the growth and reproduction of yeast is very slow. With the increase of temperature, its regeneration speed is accelerated. When the temperature exceeds 35℃, the growth of yeast will be inhibited and the reproduction rate will be slowed down rapidly. At 40°C, the yeast stops germinating and starts to die. If you want to get high alcohol concentration of fermentation solution and reduce alcohol consumption, you must control the fermentation temperature.
2、The effect of air on fermentation
Yeast needs air to reproduce. In the case of complete isolation from air, yeast reproduction stops for several generations. With a little air exposure, yeast can continue to reproduce. If there is no air for a long time, most of the yeast will die. In order to maintain yeast fermentation for a long time, a small amount of oxygen must be provided.
3、The types of yeast in grape juice
The types of yeast in grape juice can be roughly divided into the following three categories.
The first type is the yeast that plays a major role in fermentation, i.e. wine yeast. This yeast has strong fermentation ability, good wine flavor and many beneficial by-products. Before fermentation of the must, this yeast accounts for a very small percentage. During fermentation, this yeast multiplies rapidly and performs the main fermentation tasks.
The second group is the yeast that is present in large quantities in the must but has little fermentation capacity, represented by the tip yeast. The ratio of tip yeast to wine yeast is about 1000:1 in freshly pressed must, and this weak yeast is the first to cause fermentation at the beginning of fermentation. Later in the fermentation process, its role is gradually replaced by that of wine yeast.
The third type is an aerophilic yeast that produces membranes. When the fermentation vessel is not full, the membrane-producing yeast grows and multiplies on the liquid level of the must, causing the must to deteriorate. Fermentation is the most important process in winemaking. The process of turning grape juice into wine is the alcoholic fermentation of the yeast. The fermentation process is very complex. The main products are alcohol and carbon dioxide, among other by-products. It is not difficult to imagine that fermented wine would taste monotonous if the final products of fermentation were only alcohol and carbon dioxide, without the production of substances with flavor and taste.
