The majority acids in the grape are tartaric, L-malic, which represent about 90% of the total, and citric acid. In addition, during the fermentation process, other acids such as L-lactic, succinic or acetic appear that also contribute to total acidity. The total content of acids is important because it gives the wine its organoleptic characteristics, resulting in harsh wines when it is excessively high or flat, when it is too low. In addition, the total content of acids has relevance in terms of the conservation of wine, inhibiting the development of microorganisms.
Enzymatic method for sucrose, glucose and fructose measurement
In addition to monomeric hexoses (glucose and fructose), the must contains small amounts of sucrose disaccharide, which is hydrolyzed into fructose and glucose by the enzyme β-fructosidase (β-F). The natural sucrose content in the must is relatively low (and zero in the finished wine), and its addition is specifically prohibited in some countries. However, the addition of sucrose is a specific practice of the process of the production of sparkling wines (second fermentation) and in the captalization (to increase the alcoholic strength artificially, in specifically authorized areas). The determination of the total sugar content, including the one derived from the hydrolysis of sucrose, improves the control of the fermentation process both at its beginning and at the end (residual sugars), improving its general control.
Potassium is the most abundant cation in wine. Its concentration depends both on the grape variety, the soil conditions, the collection procedures (presence of scratches) and the methods used in winemaking. High values of potassium in the grapes will lead to more basic musts, which could adversely affect the quality of the wine. Although most of the potassium salts are soluble, potassium bitartrate decreases its solubility as the concentration of alcohol increases, giving rise to precipitates that, although they do not affect the organoleptic properties of the wine, can be perceived as a decrease in quality.
Colorimetric method for total polyphenols measurement
The phenolic compounds of wine (natural phenols and polyphenols) are a broad group of chemical compounds that affect the taste, color and mouthfeel of the wine that come from the skin, pulp and seed of the grape. The specific distribution of the same is that which gives the wine its own characteristics, identifying the type of grape used and the process of elaboration. Its main function is to control the natural oxidation of the wine during the ripening and aging process and increase the stability of its organoleptic properties.
Most of the lactic acid present in the wine is produced during the malolactic fermentation with the transformation of L-malic acid into L-lactic acid, so that more than 75% of the lactic acid present in the wine is the L isomer. D-lactic acid, on the other hand, is associated with the metabolism of glucose (and other hexose sugars) by the same lactic bacteria (mainly leuconostoc and lactobacillus). A presence of D-lactic acid greater than 0.3 g/L is an indication of bacterial contamination, since these bacteria compete with the yeasts for sugars, until inhibiting alcoholic fermentation.