Evaluation of the effects of nutrient supplementation on low nitrogen Chardonnay Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/k0698c09k

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  • Low nitrogen Chardonnay juice from an Oregon winery was fermented with a series of nutrient supplements, including diammonium phosphate (DAP), Fermaid K, Superfood, yeast extract, yeast hulls and thiamine. These treatments were evaluated for their contribution to the yeast assimilable nitrogen content (YANC) of the juice, which consists of the ammonium ion and α-amino acid content by NOPA (nitrogen by ophthaldialdehyde). The fermentation characteristics and the nutritional and chemical status of the finished wines were compared. Diammonium phosphate added 25 mg N/L from ammonia for every pound/1000 gallons (12.5 g/hL) used. Commercial yeast nutrient preparations were found to contribute around 10 mg N/L from ammonium ion per pound/1000 gallons (12.5 g/hL). NOPA and HPLC analysis of Superfood and Fermaid K indicated that they contributed only a small amount of amino acids. NOPA analysis of PL-50 yeast extract indicated that it may have added some nitrogen from amino acids. Nitrogenous compounds were taken up within the first few days of fermentation. Ammonium ion was depleted very quickly and did not reappear later in fermentation. Alpha-amino acids reached a low within approximately ten days of fermentation, then leveled out or increased towards the end of fermentation. Treatments containing high amounts of ammonia were observed to produce the most vigorous fermentations. These treatments were found to have the highest apparent levels of amino acids at the end of fermentation. The Control treatment, which had the lowest YANC content, appeared to utilize proline during fermentation. Sensory analysis was not conducted on the finished wines due to replication differences in reduced sulfur aroma found in preliminary screening. GC-MS analysis showed that the higher nitrogen treatments had levels of reduced sulfide compounds that were above sensory threshold, whereas moderate nitrogen treatments did not. Ethyl carbamate was not found in any of the finished wines. These data suggest that moderate levels of supplementation had a positive effect on both fermentation and finished wine quality. Higher levels of nutrient addition were effective at increasing fermentation rates but negatively affected the sulfide profile of finished wines.
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