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Influence of the Timing of Nitrogen Additions during Synthetic Grape Must Fermentations on Fermentation Kinetics and Nitrogen ConsumptionHigher alcohols were also affected by the changes innitrogen utilization. These compounds can be producedeither by the catabolic conversion of the branched-chainamino acids (via Ehrlich) or by the anabolicformation of these amino acids de novo froma sugar substrate (14, 15). Our results show that theanabolic route is of greater importance because theincrease in isoamyl alcohol and 2-phenyl ethanol wasinversely proportional to the consumption of leucineand phenylalanine, respectively.Furthermore, the closer the nitrogen concentrationis to the growth-limiting level, the higher the yield offusel alcohols is.There is also an inverse correlation between ammoniumconsumption and the production of fusel alcohols(12). A greater concentration of higher alcoholsdid not seem to determine an increase in esters. Incontrast, the acetate concentration seemed to determinea greater concentration of acetate esters, especiallyethyl acetate.In conclusion, our study shows the quantity and qualityof the nitrogen demands of the wine strain QA23.Although further studies should be carried out withother wine strains, our data show that cell growthand fermentation have different preferred nitrogensources. Nitrogen additions always improved fermentationperformance but had a minimal effect on biomassproduction when added in the second half ofthe fermentation. These nitrogen additions subjectedthe cells to NCR and changed the profile of nitrogenconsumption. The differences in the pattern of nitrogenconsumption were related to different aromacompound compositions in the wines. In our opinion,this study is a starting point for further investigationinto using an ammonium/amino acid mixture as nitrogensupplementation in the wine industry and theeffect that these additions have on yeast physiology,fermentation performance, and wine quality.ACKNOWLEDGMENTThis work was supported by grant AGL2000-0205-P4-03 from the Comisión Interministerial deCiencia y Tecnología, Spain.The authors wish to thank the language service of theRovira i Virgili University for revising the manuscript.LITERATURE CITED(1) Bisson, L. F. Influence of nitrogen on yeast and fermentationof grapes. In Proceedings of the InternationalSymposium on Nitrogen in Grapes andWine; Ranz, J. M., Ed.; American Society of Enologyand Viticology: Davis, CA, 1991.(2) Bely, M.; Sablayrolles, J. M.; Barre, P. Automatic detectionof assimilable nitrogen deficiencies duringalcoholic fermentation in oenological conditions.J. Ferment. Bioeng. 1990, 70, 246- 252.(3) Jiranek, V.; Langridge, P.; Henschke, P. A. Yeast nitrogendemand: selection criterion for wine yeastsfor fermenting low nitrogen musts. In Proceedingsof the International Symposium on Nitrogenin Grapes and Wine; Ranz, J. M., Ed.; AmericanSociety of Enology and Viticology: Davis, CA,1991. (4) Monteiro, F. F.; Bisson, L. F. Nitrogen supplementationof grape juice. I. Effect on aminoacid utilization during fermentation. Am. J. Enol.Vitic. 1992, 43, 1 -1 0.(5) Bely, M.; Sablayrolles, J. M.; Barre, P. Description ofalcoholic fermentation kinetics: its variability andsignificance. Am. J. Enol. Vitic. 1990, 41, 319-324.(6) Mendes-Ferreira, A.; Mendes-Faia, A.; Leao, C.Growth and fermentation patterns of SaccharomycescereVisiae under different ammoniumconcentrations and its implications in winemakingindustry. J. Appl. Microbiol. 2004, 97, 540-545.(7) Cooper, T. G. Nitrogen metabolism in SaccharomycescereVisiae. In The molecular Biology of theYeast Saccharomyces; Stratherm, J. N., Jones, E.W., Broach, J. R., Eds.; Cold Spring Harbor Laboratory:Cold Spring Harbor, New York, 1982.(8) ter Schure, E. G.; van Riel, N. A.; Verrips, C. T. The roleof ammonia metabolism in nitrogen cataboliterepression in Saccharomyces cereVisiae. FEMSMicrobiol. ReV. 2000, 24, 67- 83.(9) Beltran, G.; Novo, M.; Rozes, N.; Mas, A.; Guillamon,J. M. Nitrogen catabolite repression in SaccharomycescereVisiae during wine fermentations.FEMS Yeast Res. 2004, 4, 625-632.(10) Jiranek, V.; Langridge, P.; Henschke, P. A. Regulationof hydrogen sulfide liberation in wine-producingSaccharomyces cereVisiae strains by assimilablenitrogen. Appl. EnViron. Microbiol. 1995, 61, 461-467.48