engleski

Variations in the composition of acids in grapes of autochthonous Croatian varieties during the drying process in the production of the dessert wine Prošek

According to the scientific literature, the autochthonous varieties of grapevine Maraština, Glavinuša, Plavina and Lasina used to be the basis for the production of prošek, traditional Dalmatian dessert wine. The production of the famous wine has been neglected and recently the work on its revitalization has begun. With the objective of determining the suitability of the varieties mentioned above for this production technology, the studies were conducted in three production years (2005-2007). About 200 kg of grapes were harvested from each variety at full maturity, in typical wine-growing areas. Depending on the variety, the drying process lasted on average 15 – 20 days. Dried grapes were processed and the dessert wine, prošek was produced. The present study illustrates variations in the content of the acids most abundant in grapes (tartaric acid and malic acid) during the drying process, as well as their content in must, which represents one of the important factors of quality and organoleptic characteristics of the future dessert wine. The analysis of the composition of acids in grapes was conducted in three phases: during harvest, on partially dried grapes (7-10 days after the drying) and at the end of the drying process. Sugar in grapes was determined according to the areometric method (ºOe). Total acidity was determined using a titration method, pH value by pH-meter, while tartaric and malic acids were determined by liquid chromatography. In order to determine real, metabolic variations of the composition of acids (those which are not the consequence of the concentration of single compounds due to the dehydration of grapes), the acid content was expressed by comparing the measured concentrations of single acids to the concentration of sugar ((g/lxºOe-1)x100). During the drying process, all the varieties included in the study showed a decrease in their acid content. The largest average decrease in the three-year period was registered in the variety Lasina, while the smallest one was found in Glavinuša. The tartaric acid content in Lasina dropped by 61, 3% (from 7, 48 to 2, 90 (g/lxºOe-1)x100), while in Glavinuša it dropped by 45, 3% (from 5, 31 to 2, 91 (g/lxºOe-1)x100). All the varieties showed a slight decrease in the malic acid content ranging from the maximum of 40, 6% in the Lasina variety (from 1, 80 to 1, 09 (g/lxºOe-1)x100) to the minimum of 11, 8% (from 1, 07 to 0, 94 (g/lxºOe-1)x100) in the Glavinuša variety.

dessert wine prošek; autochthonous Croatian varieties; drying process of grapes; malic acid; tartaric acid

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