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Yeast assimilable nitrogen or YAN is the combination of Free Amino Nitrogen (FAN), ammonia (NH3) and ammonium (NH4+) that is available for the wine yeast ''Saccharomyces cerevisiae'' to use during fermentation. Outside of the fermentable sugars glucose and fructose, nitrogen is the most important nutrient needed to carry out a successful fermentation that doesn't end prior to the intended point of dryness or sees the development of off-odors and related wine faults. To this extent winemakers will often supplement the available YAN resources with nitrogen additives such as diammonium phosphate (DAP).〔B. Zoecklein, K. Fugelsang, B. Gump, F. Nury ''Wine Analysis and Production'' pgs 152-163, 340-343, 444-445, 467 Kluwer Academic Publishers, New York (1999) ISBN 0834217015〕 However, the addition of excessive amounts of nitrogen can also create a hazard as other organisms besides beneficial wine yeast can utilize the nutrients. These include spoilage organisms such as ''Brettanomyces'', ''Acetobacter'' and Lactic acid bacteria from the ''Lactobacillus'' and ''Pediococcus'' genera. This is why many wineries will measure the YAN after harvest and crushing using one of several methods available today including the nitrogen by o-phthaldialdehyde assay (NOPA) which requires the use of a spectrometer or the Formol titration method. Knowing the YAN in the must allows winemakers to calculate the right amount of additive needed to get through fermentation, leaving only "nutrient desert" for any spoilage organisms that come afterwards.〔K. Fugelsang, C. Edwards ''Wine Microbiology'' Second Edition pgs 16-17, 35, 115-117, 124-129 Springer Science and Business Media , New York (2010) ISBN 0387333495〕 The amount of YAN that winemakers will see in their grape musts depends on a number of components including grape variety, rootstock, vineyard soils and viticultural practices (such as the use of fertilizers and canopy management) as well as the climate conditions of particular vintages.〔R. Jackson ''"Wine Science: Principles and Applications"'' Third Edition pgs 90-98, 151, 167, 183, 305-310, 356-357, 375-387, 500, 542 Academic Press 2008 ISBN 9780123736468 〕 ==Components== YAN is a measurement of the primary organic (free amino acids) and inorganic (ammonia and ammonium) sources of nitrogen that can be assimilated by ''S. cerevisiae''. There are several nitrogenous compounds found in must and wine including peptides, larger proteins, amides, biogenic amines, pyridines, purines and nucleic acids but these cannot be directly used by yeast for metabolism. Taken together, the total nitrogen content of grape must can range from 60 to 2400 mg of nitrogen per liter, however not all of this nitrogen will be assimilable.〔 The lack of protease enzymes, which break down larger peptides into smaller components, that can work outside the cell limits the size of the molecules that yeast can used as a source for nitrogen.〔〔R. Boulton, V. Singleton, L. Bisson, R. Kunkee ''Principles and Practices of Winemaking'' pgs 46-48, 80-81, 153-167, 256 Springer 1996 New York ISBN 978-1-4419-5190-8〕 The amount of YAN that winemakers will see in their grape musts depends on a number of components including grape variety, rootstock, vineyard soils and viticultural practices (such as the use of fertilizers and canopy management) as well as the climate conditions of particular vintages. Infections by mold, such as ''Botrytis cinerea'' (known as noble rot when it is desired) can reduce the amino acid content of grape must by as much as 61%.〔 Some regions are noted for having low YAN such as Washington State which during a typical vintage will have 90% of tested must be below 400 mg N/L〔 Sara E. Spayd and Joy Andersen-Bagge ''"(Free Amino Acid Composition of Grape Juice From 12 Vitis vinifera Cultivars in Washington )"'' Am. J. Enol. Vitic 1996 vol. 47 no. 4 389-402 〕 and nearly a quarter be below 150 mg N/L.〔 In the vineyard, nitrogen is taken up by the grapevine as nitrate (NO3−), ammonium or urea which gets reduced into ammonia. Through additional reactions the nitrogen is incorporated into glutamine and glutamate and eventually used in the synthesis of other amino acids and nitrogenous compounds.〔 After harvest, the majority (around 80%) of available nitrogenous compounds found in the grapes are concentrated in the skins and seeds. These compounds get released into the must during the process of crushing and during maceration/skin contact.〔 Even after pressing up to 80% of initial nitrogen content within each grape berry will be left behind in the pomace.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Yeast assimilable nitrogen」の詳細全文を読む スポンサード リンク
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