Vinification, flavor, and aroma

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Photo of Rahovec Grapes, a common fruit used for vinification.

Wine making, or vinification is a process, through which fruit juice, usually from grapes, is fermented to produce an alcoholic drink. Once fruit is harvested, it is the wine makers duty to ferment the juice into a palatable wine through complex interactions of yeast and bacteria. Fermentation can be achieved using the natural grape must, naturally occurring yeast on machinery and vines, or by inoculating batches with commercially produced yeasts. Vinification requires the careful management of the microflora present, nutrient availability for the microflora, pH, temperature, and storage conditions, in order to make a palatable vintage.

The perception of a wine’s flavor and aroma comes from a multitude of interactions between about a 1,000 chemical compounds within the wine and our own sensory receptors. These chemical compounds function in many different ways, and can act synergistically or antagonistically with each other. Flavor and aroma compounds are derived from the grapes themselves, the wood fermentation occurs in, and the metabolites of microbes used in the fermentation process. Making a tasty wine is largely related to the ratios of volatile compounds found in the wine; wines with out enough of a certain compound will lack flavor and fullness, while wines with too much of a compound can taste spoiled. These compounds result from primary, secondary, and malolactic fermentation processes.

One other aspect of wine flavor and aroma comes from yeast assimilable nitrogen. Yeast assimilable nitrogen (YAN) is the amount of nitrogen available for yeast during the fermentation process. YAN is inherent to grapes, and can be measured after harvesting and crushing, but can also be controlled by the wine maker to reduce the likelihood of spoilage.

Microbial Processes of Vinification

Malolactic Fermentation

Electron micrograph of the Ebola Zaire virus. This was the first photo ever taken of the virus, on 10/13/1976. By Dr. F.A. Murphy, now at U.C. Davis, then at the CDC.

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Legend/credit: Electron micrograph of the Ebola Zaire virus. This was the first photo ever taken of the virus, on 10/13/1976. By Dr. F.A. Murphy, now at U.C. Davis, then at the CDC.
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Compounds That Effect Flavor and Aroma

Include some current research in each topic, with at least one figure showing data.

Yeast Assimilable Nitrogen

Include some current research in each topic, with at least one figure showing data.

Further Reading

[Sample link] Ebola Hemorrhagic Fever—Centers for Disease Control and Prevention, Special Pathogens Branch

References

Styger, Gustav, Bernard Prior, and Florian F. Bauer. "Wine flavor and aroma." Journal of industrial microbiology & biotechnology 38.9 (2011): 1145-1159.

Heard, Gillian M., and Graham H. Fleet. "Growth of natural yeast flora during the fermentation of inoculated wines." Applied and Environmental Microbiology 50.3 (1985): 727-728.

Heard, Gillian M., and Graham H. Fleet. "Growth of natural yeast flora during the fermentation of inoculated wines." Applied and Environmental Microbiology 50.3 (1985): 727-728.

Romano, P., et al. "Function of yeast species and strains in wine flavour." International journal of food microbiology 86.1 (2003): 169-180.

[www.ftb.com.hrfiles/journals/1/articles/183/public/183-182-1-PB.pdf Romano, Patrizia. "Metabolic characteristics of wine strains during spontaneous and inoculated fermentation." Food Technology and Biotechnology 35 (1997): 255-260.]

Edited by Patrick Niedermeyer, a student of Nora Sullivan in BIOL168L (Microbiology) in The Keck Science Department of the Claremont Colleges Spring 2014.