Effects of cryoconcentrate addition on the alcoholic fermentation of grape juice

Sugar concentration is one of the main factors in alcoholic fermentation (AF). Thus, the influence of high concentration of sugars on the AF of grape juice was evaluated. Grape juice (GJ) (18.31 ± 0.03 °Brix) originated cryoconcentrate 1 (C1) (31.13 ± 0.20 °Brix) and C1 originated cryoconcentrate 2 (C2) (42.45 ± 0.09 °Brix). Then, five treatments (T) and a volume of 1.5 L of each were formulated: T1 (100% GJ), T2 (36.15% GJ + 63.85% C1 with 27.64 ± 0.27 °Brix), T3 (64.42% GJ + 35.58% C2 with 27.62 ± 0.02 °Brix), T4 (100% C1) and T5 (100% C2). In each formulation, 0.05 g L-1 of potassium metabisulphite was added. After 4h, each treatment was inoculated with Saccharomyces cerevisiae (0.60 g L-1) and incubated at 23.0 ± 2.0 °C. The duration of AF was 10 days for T1, 26 days for T4 and 18 days for T2, T3 and T5. The alcohol content and total residual reducing sugar content achieved was 10.56% ± 0.01% and 4.22 ± 0.42 g L-1 in T1, 14.58% ± 0.03% and 34.53 ± 0.20 g L-1 in T2, 14.91% ± 0.03% and 35.88 ± 0.56 g L-1 at T3, 10.37% ± 0.03% and 76.03 ± 1.55 g L-1 at T4 and 5.26% ± 0.02% and 208.50 ± 5.57 g L-1 at T5. All treatments showed a significant difference (Tukey's test: p < 0.05) and was observed that the high sugar concentrations reduced the fermentative capacity of yeasts (T4 and T5 results). Probably the reason for this result is due to the decrease of free water for AF of the grape juice. Thus, alcohol production is directly proportional to the sugar content up to the limit where yeasts can act in the fermentation medium.