Colorimetric method for primary amino anitrogen measurement
Yeasts need nitrogen to grow. One of the main sources of nitrogen are the proteins, peptides and amino acids present in the medium (primary amines, PAN); the other main source is the ammonium ion itself. The determination prior to the fermentation of the amount of assimilable nitrogen makes it possible to adjust it adequately to avoid unexpected stops of the fermentation process due to nitrogen deficit.
Sulfites are produced naturally during fermentation, but they are also added to the wine in order to stop the fermentation process (for example, the delay of malolactic fermentation in the presence of sulfites is well-known). A good part of sulfite is reversibly linked to other compounds such as sugars or polyphenols. The free sulfite (either in the form of SO2, HSO3- or H2SO3), on the other hand, acts as a preservative to prevent deterioration both due to its antioxidant capacity and its antimicrobial action. Free sulfite has been associated with different allergic reactions, so its specific determination is a legal requirement in many countries.
Sulfites are produced naturally during fermentation, but are also added to stop the fermentation process. In wine, they act as preservatives to prevent deterioration due to both their antioxidant capacity and their antimicrobial action. The concept of total sulfites referers to any sulfite present either in the form of anhydrous sulphur (SO2), bisulfite ion (HSO3) or sulfurous acid (H2SO3), but also other forms linked to other compounds such as sugars or polyphenols. It is necessary to control the maximum concentration of sulfite present since at high concentrations it can be toxic.
Calcium is a natural element in the must, although in certain manufacturing processes calcium salts (calcium carbonate for acidity reduction) and other calcium-rich substances (casein for clarification) can be added. The solubility of calcium decreases with increasing alcohol content, easily reaching supersaturation. In these cases there is a risk of causing calcium tartrate precipitates (and in some cases calcium oxalate) during aging inside the bottle, since its formation is very slow. This problem is particularly relevant in white wines because of its visibility. The control of calcium levels makes it possible to force the precipitation of said crystals, and their subsequent filtration, as part of the manufacturing process.
Catechins are a group of flavonoid polyphenols found mainly in the seeds and to a lesser extent in the skin. They occur naturally as a defense mechanism against berry infections, so their concentration is higher in varieties grown in humid weather. They are responsible for the bitter notes in the taste of the wine and, because they have antioxidant properties, they contribute to provide color stability during the ripening process. The content of catechins in the sample is directly related to the crushing process and the period of contact with the grape skin.