Malic acid, both in free and esterified form, is usually present in ripening fruit and is responsible for the astringent taste of the unripe fruit. Its concentration is reduced as it matures. In the process of winemaking, more than 30% of the malic acid is transformed by a process of fermentation in lactic acid (malolactic fermentation) that helps to reduce the initial acidity of the must. Control of the malic acid level is necessary to maintain the desired taste, acidity and astringency characteristics of wine.
Enzymatic method for glucose and fructose measurement
D-Glucose and D-Fructose are the main reducing sugars present in grapes and other fruits. Its determination in the grape allows to verify their state of maturity to establish the optimum moment of harvest. In the must, allows to estimate the amount of alcohol that will be produced during the fermentation. Finally, at the end of the fermentation, to assess the remaining sugar that could produce an undesired fermentation.
Tartaric acid is the main component that gives the wine its characteristic acidity, being present both in its acid form and in the form of potassium salt. From the point of view of production it is a critical element in the development of color and flavor during the wine ripening process, as well as its subsequent chemical stability. The determination of tartaric throughout the manufacturing process allows to keep track of its organoleptic evolution.
Anthocyanins are primarily responsible for the color in red wine and especially contribute to the astringency sensation of the wine. At the beginning of the maturation process they form simple complexes with other compounds present in the wine giving rise to a progressive change in the color of the wine (turning to blue tones) but as maturation progresses these compounds tend to form other compounds (often polymers) a lot more stable in color with respect to pH and sulphites. The proportion between the different compounds present (simple and polymeric) is directly related to the final color obtained and its stability. This determination allows the concentration of non-polymeric (ionizable) anthocyanins to be established.
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.