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August 2018 WINES&VINES 41 PRACTICAL WINERY & VINEYARD WINEMAKING by free amino acids) are used by yeasts both for the production of structural proteins and the enzymes that take part, to a varying de- gree, in the fermentation process. In addition to free amino acids, the must also contains nitrogen as peptides and protein, but these two forms of nitrogen are not used by yeasts due to their lack of proteasic activity. In the presence of low levels of YAN, the measurement and the consequent integration of inorganic (ammonium) and organic (amino acidic) forms becomes a fundamental require- ment for an optimal alcoholic fermentation. Determination of levels of inorganic and or- ganic nitrogen, and correction of deficiencies, is therefore crucial for an optimal fermenta- tion. Nitrogen supplementation becomes even more important with the high-sugar musts typical of warm vintages. It is no surprise that the analysis of YAN has been recognized in recent years as a fundamental analysis to cre- ate high-quality wine. Absorption of YAN and effect on fermentation Knowledge of the assimilation mechanisms of YAN and the consequences of insufficient amounts is important to correctly plan and manage alcoholic fermentation. Ammonium absorption and amino acids within the yeast cell occur by means of protein transporters. S. cerevisae possesses at least four of them: two for inorganic nitrogen, two for organic nitro- gen. For the latter, there are selective transport- ers according to the type of amino acid and non-selective transporters, commonly called general amino permease (GAP). For both assimilable nitrogen forms, the mechanism of entry into the cell is active in contrast to what occurs with glucose and fruc- tose, which flow into the cellular cytosol by passive diffusion. In the early stages of alcohol fermentation, the relatively high concentration of ammonium ions inhibits the non-selective GAP that regulates amino acid nitrogen intake. ENZYMATIC GLUCOSE OXIDATION Figure 3: Glucosidase of Botrytis catalyzes the oxidation of D-glucose, forming D-gluconic acid. ENZYMATIC D-GLUCONIC ACID OXIDATION Figure 4: Oxidation of D-gluconic acid by Gluconobacter bacteria with the formation of 5-oxo- gluconic acid, 2-oxo-gluconic acid and 2,5 dioxo-gluconic acid. 145 Jordan Street, San Rafael, CA 94901 415-457-3955 • www.boswellcompany.com he Premier Silicone Rubber Bung T ee ee e e4Z e Autoanalyzers, Reagents, Fast Service, Great Quality 30 great : GF, ML, AMM, NOPA, Acetic, free & total SO 2 , tartaric, phenolic panel & more! & e-Z[ ee ee eSemi-automated, portable ee ee eeeeeeeeeee ee e100-tests/hr ee ee eeeeeeeee e eee Auto-washing, 200 tests/hr Order online www.unitechscientiic.com Contact us info@unitechscientiic.com Phone: 562 924-5150 Wine Analyzers: /FX 8 . in 2-hr