The Impact of Berry Maturity on Phenolic Content
June 19, 2019
I usually try to keep an eye on the Harbertson Lab’s publications, but it looks like I didn’t mention this one when it was published back in January 2018. Phenols, especially polymeric pigments, are generally known to be important for wine color, astringency, and general mouthfeel, but so much about their development and polymerization during aging is uncertain that I am always looking for more research on the subject. In this paper, the exploration of phenolic hydrophobicity was especially interesting even if, in retrospect, the findings were more or less what I expected.
In this study, grape cultivar, fruit maturity, and alcohol were varied to determine their impacts on polymeric pigment formation in artificially aged wines. Polymeric pigments are formed primarily, but not exclusively, through the reaction of anthocyanins and tannins during wine aging. Two cultivars (Syrah and Cabernet Sauvignon) that differ in their native anthocyanin and tannin content were harvested at three maturities (20, 24, and 28 Brix) in order to vary the initial anthocyanin and tannin content and their ratio (A:T). At each harvest, juice sugar content was manipulated in the winery to simulate the two other respective maturities. The range of initial wine A:T varied by cultivar (Cabernet Sauvignon, 0.36 to 0.93; and Syrah, 1.3 to 2.1). Results of two-way ANOVAs indicated that fruit maturity and wine age significantly affect anthocyanin content and decline, as well as small polymeric pigment formation. The anthocyanin decline could be modeled by an exponential decay regression, with R2 values ranging from 0.996 to 0.999, depending on maturity and cultivar. Winery alcohol treatment and time significantly impacted the formation of large polymeric pigments. The initial wine anthocyanin content had the strongest correlation to total polymeric pigment content in wines (R2 of 0.735 and 0.670 for Syrah and Cabernet Sauvignon, respectively), while the relationship between A:T and total polymeric pigments was relatively poor (R2 of 0.042 and 0.405 for Syrah and Cabernet Sauvignon, respectively). Measuring wine phenolic hydrophobicity is also proposed to evaluate overall phenolic characteristics, and it was significantly impacted by cultivar, fruit maturity, and aging time.