Variety and storage time affect the compositional changes that occur in grape samples after frozen storage

Background and Aims: In viticultural and oenological research, grape samples are frequently stored frozen to overcome time and facility restraint. However, there is little knowledge on how freezing, variety and storage time affect the changes occurring in grape quality parameters. The aim of the paper was to evaluate these effects using cv. Cabernet Sauvignon (CS), Grenache (GA) and Tempranillo (TE) samples. Methods and Results: Quality parameters were assessed in fresh grapes and after 1, 3 and 6 months of frozen storage. Soluble solid concentration remained unchanged. Freezing decreased titratable and tartaric acidity. pH increased after 1 and 3 months of storage, but decreased after 6 months. Freezing increased malic acid concentration only in GA. Yeast assimilable nitrogen diminished with freezing time, with each variety behaving differently. A significant colour enhancement was found (EAnt, L*, C*), whereas degradative reactions for polyphenols occurred at any storage time for GA, and for all varieties after 6 months. Conclusions: Variety and storage time play a large role in the changes occurring in stored frozen grape samples. Not considering these factors may lead to misinterpretation of results obtained through subsequent use of these grapes. Significance of the Study: Specific correcting factors for each quality parameter, variety and storage time are needed when working with stored frozen samples.