The Chemical Evolution and Preservation of Color in Red Wine Aging

AVF Proj. ID: 222 / /Cat.:
Primary Investigator(s): Andrew Waterhouseby

Color of red wine is the first attribute observed by the consumer and it can condition the overall evaluation of wine. The molecules with red pigmentation are called anthocyanins and their chemistry is extremely complex during wine aging. This complexity comes from the large amount of products formed throughout wine maturation that are difficult to separate and identify.During the past year we were able to add a radioactive anthocyanin to a young wine. This experiment allows tracking the pigment even after the formation of complex products or molecules that have lost the pigmentation. Different aging conditions such as temperature, pH, tannin concentration, oxygen exposure and co-pigmentation were studied in order to obtain practical information. All of these variables are factors that can be controlled by the wine maker. Results indicate that in an aged wine it is possible to find most of the anthocyanins incorporated into polymeric structures. Furthermore, these polymers change over time, altering their visible absorbance. Radioactive tracing also allows monitoring the precipitation of polymers, which leads to color loss and reduction of astringency. Variables such as wine pH, additional tannin levels or co-pigmentation have small effects. However, oxygen exposure and temperature had large effects in the course of polymeric pigment formation.Another experiment allowed us to monitor the pigments during fermentation. Previous reports have shown that during the first days of fermentation there is an increase in concentration caused by extraction from skins followed by a decrease caused by reasons not very well defined. After adding a radioactive anthocyanin we were able to determine that at one point half of the anthocyanins are reversibly associated with solids. In addition, the decline of malvidin-3-glucoside at late stages of fermentation does not correlate with a decrease of radioactivity in solution indicating that chemical transformation of anthocyanins is taking place.