Assessment of the validity of maturity metrics for predicting the volatile composition of Concord grape juice.

Total soluble solids (TSS) are typically used as the sole metric for maturity of Concord grapes. However, the reliability of TSS in predicting the aroma composition of finished juice for grapes sourced from multiple sites has not been investigated. This study sought to determine the validity of TSS in predicting the aroma composition of the juice while also investigating other potentially useful indicators, including pH, titratable acidity (TA), and TSS:TA ratio. Grapes were harvested from 9 sites in the Lake Erie Concord Grape Belt and stratified from north to south and east to west. The key aroma compounds methyl anthranilate ("grapey") and trans-2-hexenal ("herbaceous") were quantified along with several other odorants. It was observed that while TSS was a robust predictor of monomeric anthocyanin content across sites, it was a poor predictor of aroma compounds in the finished juice. Conversely, pH, TA, and TSS:TA ratio were all significantly correlated with methyl anthranilate and trans-2-hexenal concentrations (P < 0.05) in samples equal to or exceeding 15 Brix, the industry minimum for grape maturity. These results indicate that parameters related to acidity are better predictors of aroma composition than TSS, which may aid in efforts to minimize herbaceous off-aromas and optimize the aroma composition of the finished juice.