Nitrogen grape

Regulations specify a considerable Hst of additives and treatments which may be permitted under controlled limits and conditions. It is important to note that no wine receives mote than a few of these treatments, and many have none. For example, most grape musts ferment readily without additions, but some extra nitrogen source for the yeasts is occasionally beneficial. If some is requited, ammonium phosphate is the most commonly used. 

Grape and apple juices usually contain all of the trace nutrients required by Saccharomjces for fermentation of sugars to alcohol. Other fmit and diluted honey, as well as barley malt and rice extract, frequendy need additions of nitrogen, phosphoms, and potassium compounds, together with some autolyzed yeast to faciUtate the yeast growth necessary for fermentation. Stimulation oiy4.cetobacter frequendy requires the addition of autolyzed... 

Plants (cereals, cotton, potato, citrus, apple, pear, peach, grape, persimmon, apricot, chestnut), soil and water Gas-chromatographic determination [mass spectromet-ric detection (MSD), flame thermionic detection (FTD) or nitrogen-phosphorus detection (NPD)] for plant materials, water and soil... 

Interpretation of the process of fermentation by yeast was one of the most controversial issues for vitalists. Its resolution was fundamental for the future development of biochemistry. In the early nineteenth century fermentation was believed to be related to putrefaction and decay. Liebig considered it to result from the breakdown of a substance (sugar) following the admission of air to the nitrogenous components in yeast juices. After the must of grape juice had fermented, the liquid cleared and the yellow sediment, yeast, was deposited. 

Bound precursors of lAA, their enzymatic cleavage by yeasts as well as the nitrogen content of the grape juice seem to govern 2-AAP formation as well... 

The ammonia nitrogen of grapes is quite variable. Studies have shown that the ammonia content of musts is associated with maturity,... 

The Scuppemong grape has a distinctive flavor characteristic. Kep-ner and Webb (47) analyzed the volatile essence of this grape and identified six alcohols, including 0-phenylethyl alcohol, five aldehydes, and five esters. No nitrogen or sulfur containing compounds were found which indicated the absence of methyl anthranilate. 

At the end of the fermentation the wine will be turbid and muddy from the suspended yeast cells and the debris from the fruit. Most of this material will settle quickly, forming a more or less thick layer in the bottom of the bottle. The new wine should be syphoned away from the deposited sediment promptly to avoid off flavors from autolysis of the yeast in the sediment. Also at this time wine acquires the defect of H2S which is produced by reduction of the elemental sulfur dust applied to the grapes as fungicide by the decomposing yeast cells in the thick layer of sediment. The first transfer of the new wine from the sediment should occur very soon after active fermentation, the second about two weeks later, and the third and possibly a fourth two to six months later. These rackings may be conducted under a blanket of nitrogen or carbon dioxide if the particular wine oxidizes easily. 

Kliewer WM. 1977 Influence of temperature, solar radiation and nitrogen on coloration and composition of Emperor grapes. Ant J Enol Vitic 28 96-103. 

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