Chemical composition of wine 
part of the sugars, glucose and fructose fermentation damage while the galactose is fermented with difficulty. In wines we find the presence of other compounds that belong to the group of sugars such as aldoses arabinose and xylose (already present in the must) rhamnose and ribose: the latter comes from the metabolism of yeasts. On sugar, therefore, act not only bacteria but also yeasts homolactic that can transform glucose and fructose into lactic acid bacteria and heterolactic that metabolize sugars into lactic acid and acetic acid and are responsible for the defect referred to as the starting lactic, occur when the temperature of 'environment is too high, stopping the fermentation, the fermentation heterolactic leading to the production of other compounds harmful to the structure and aroma. Should also be defined as the development of bacteria Acetic acid on grape Unsound increases the volatile acidity in wine. After ethanol, present in quantities ranging from 50 to 200 g / l, glycerol, also known as glycerin, is alcohol present in wine in larger quantities (8-10 g / l) and can be present from the starting juice from grapes "moldy" from botrytis (Botritis cinerea) or from healthy grapes. Acetic acid is already present in the must and can be an increase in its concentration in wine by acetic acid bacteria that attack the format and process it into ethanol (in presence of oxygen) respectively in the above-mentioned through the intermediate step in the compound acetaldehyde . The work of the terrible acetic acid bacteria also includes the formation of ester (chemical compound formed from an acid and an alcohol) to the combination of acetic acid and ethanol with the consequent production of ethyl acetate, acetic main actor of the cue. Compared to the must in wine there is a decrease in the concentration of tartaric acid and instead the new presence of succinic acid. The structure of the water must first be transformed during the fermentation process in water and ethanol and this results in a lower solubility of salts present in wine such as potassium and calcium tartrate. The yeasts in the must consume various items such as calcium, sulfates and phosphates that find themselves with lower concentrations in the finished drink.
In vinification of red grapes were cut in a handover of substances containing nitrogen (N) from solid parts of the raw material to the juice that ferments, some of these substances are demolished and are being transformed by the action of yeast during the process: this is the case ammoniacal nitrogen and the amino acid proline is for a yeast nitrogen tank that can be used in case of shortcomings of the element: that is why its concentration in wine is variable, usually greater than the juice, and preserves the predominance of the amino acids of the alcoholic beverage. In the must, however, there are few polyphenols and color is very pale, because the dyes were observed only nel vino rosso dopo la macerazione.
In caso di vinificazione in bianco diminuiscono le sostanze colloidali per la demolizione svolta nel mosto da specifici enzimi ( la pectinmetilesterasi e la poligalatturonasi) sulle pectine, molecole complesse formate da tante unità di acido galatturonico , in generale, nel passaggio dal mosto al vino diminuisce l'acido galatturonico ed aumenta il mannosio, derivato dall'attività dei lieviti. E' vero anche che una minore quantità di polifenoli significa più proteine in soluzione e rischio di successive precipitazioni con le conseguenti "casses proteiche" di cui parleremo quando affronteremo i "difetti" del vino. Nei vini rossi invece, per la grande quantità di polifenoli presenti, le proteine is insoluble grape solids and spent many colloids resulting haze: we must take action to remedy the problem correctly.
