D-Glucose and D-Fructose are the main reducing sugars present in grapes and other fruits. The content of D-glucose and D-fructose in grapes is similar (in a ratio between 0.74 and 1.12), with small variations depending on the ripeness of the grape and its variety. Since D-glucose is fermented more rapidly by yeasts, monitoring the relationship between D-glucose and D-fructose, in addition to its total sum, provides information on both the fermentation process and the final degree of expected sweetness. Fructose levels are calculated from the total glucose and fructose content (code SY2404) by directly subtracting the glucose content.
Glycerol (or glycerin) is a natural byproduct of alcoholic fermentation, providing body-to-mouth sensation. The glycerol content is directly related to the degree of maturity of the grape, the microorganisms present and the fermentation procedure used (temperature, yeast species, nitrogen source).
The color of the wine is the result of the mixture of different colored compounds, mainly of reddish tones (mainly anthocyanins), blue (iron complexes) and yellow (catechins). The color index is an indicator that takes into account absorption at 420, 520 and 620 nm.
The presence of copper in wine is common due to both the phytosanitary treatments carried out on the grapes, as well as the controlled addition of copper salts as part of the winemaking process. Most of the copper is precipitated in the form of sulphides and subsequently filtered. However, a high residual concentration thereof is toxic and can severely affect the alcoholic fermentation process, accelerate phenolic oxidation, cause turbidity and produce precipitates in reducing media. The control of copper concentration is essential to ensure both stability during the ripening process and ensure safe consumption.
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.