# New Isolated Autochthonous Strains of _S. cerevisiae_ for
## 3 Results and Discussion
### Physicochemical Analyses of the Obtained Wines
especially desirable in white wines. In winemaking technology, it is important to maintain the right balance between the content of sugars and organic acids [21]. The esterification of organic acids and alcohols leads to the formation of ethyl esters. These compounds are formed in all wines during maturation and contribute to the improvement of the wines' aroma. Thus, the concentration of organic acids decreases with the progressive aging of the wines [21]. Excessive concentration of organic acids can lead to an overly sour taste, which is mainly caused by malates [63; 64]. These compounds determine the pH of the wine, which is based on the balance between protein and aprotic isoforms of organic particles, determining the content of organic acids and the degree of amino acid ionization in wines [1]. This, in turn, affects the solubility and the state of ionic and biological activity of other compounds, such as proteins, phenolic compounds, or fatty acids [1; 65]. Even a slight change in pH (by 0.05 units) causes a change in acidity (0.2-0.5 g/L), which translates into a change in the organoletic characteristics of the wine [1; 66]. Aidity also affects the microbiological stability of the product, the course of malotactic fermentation, color, and wine maturation processes [21; 64; 66]. For wine making, the must pH should be in the range 3.0-3.7. At a lower pH value, the must is too acidic and yeast fermentation more slowly, while at a higher pH value, the risk of the development of undesirable microorganisms increases [67]. At a pH above 3.5, increased growth of lactic acid bacteria and a partial conversion of glucose to lactic and acetic acids may occur. Consequently, it is possible to obtain a wine with significantly increased volatile acidity and low alcohol concentration [67]. In the case of the grape must, its pH was 3.21, and in the case of the grape pulp, it was 3.81. The total sugar content of the white and red wines (Figure 6) in all samples was below 5.0 g/L, which corresponds to the dry wines. In most cases, white wines were characterized by a higher content of residual sugars compared to red wines. The main component of dry matter of grapes are sugars, the content of which reaches up to 25% (in Polish conditions, most often 17-23%) and may be even higher in overripe, dried, or covered with noble mold (_Botrytis cinerea_) fruit [68]. The main sugars in grapes are glucose and fructose [30], but in grapes must and wine fructose is present in higher concentrations than glucose [69]. Sugars are contained in the flesh of the grapes, especially in the middle of the fruit, and their amount and stabilization at an appropriate level are an indicator of the ripeness of the berries [70]. After the fermentation process is complete, the wine has a so-called residual sugar, which consists mainly of unfermented pentoses and small amounts of glucose and fructose. The division of wines by content of residual sugar varies depending on the country of origin of the product. In Poland, dry wines contain up to 10 g of residual sugar per liter of wine, semi-dry wines 10-30 g/L, semi-sweet 30-60 g/L, and sweet 60-150 g/L, and very sweet from 150 g/L. In Austria and Germany dry wines contain up to 4 g/L or up to a maximum of 9 g/L of sugar if the total acidity is not lower  
Figure 6: Total sugar content in wines of two vine varieties: white (Seyval blanc) and red (Regent) fermented with non-commercial (NCS) and commercial (CS) _S. cerevisiae._  
than 2 g/L below this value; in semi-dry wines the maximum permitted residual sugar value is up to 12 g/L or up to a maximum of 18 g/L, subject to the total acidity (measured as tartaric acid) being no less than 10 g/L below this value; semi-sweet wines contain up to 45 g/L of residual sugar, and sweet from 45 g/L of residual sugar [71; 72]. According to the above classification, all our wines can be classified as dry (sugar content below 5 g/L).