Determination of the rheological behavior and thermophysical properties of malbec grape juice concentrates (Vitis vinifera).

The rheological behavior and thermophysical properties (density, specific heat, and thermal conductivity) were experimentally determined as function of temperature (1-66 °C) and solid soluble content (13.6-45.0°Brix) for Malbec grape juice aiming at designing the unit operations involved in beverage industries. Mathematical modeling was performed to provide valuable information about the rheological behavior and thermophysical properties of Malbec grape juice at different concentrations and temperatures. The Ostwald-de Waele model fitted the concentrates rheological behavior with high accuracy. The consistency coefficients were significantly reduced by the temperature increase, following an Arrhenius relationship with activation energy ranging from 11.02 kJ/mol (45.0 °Brix) to 11.54 kJ/mol (21.0 °Brix). In contrast, they were increased by the higher concentration levels, ranging from 0.2044 Pa.sn (13.6 °Brix, 6 °C) to 20.9451 Pa.sn (45.0 °Brix, 1 °C). The flow behavior index was not influenced by temperature; however, it was strictly related to the concentration, assuming shear-thinning behavior (0.96 < n < 0.54), regardless of the solid soluble contents. Density, specific heat, and thermal conductivity were significantly correlated with both the temperature and concentration parameters by second-order polynomial models. The obtained results can be suitable for the potential use of Malbec juice concentrate as a chaptalization agent in winemaking and grape juice production.

Sensory descriptive and comprehensive GC-MS as suitable tools to characterize the effects of alternative winemaking procedures on wine aroma. Part I: BRS Carmem and BRS Violeta.

This study analyzed the volatile composition and aroma profile of BRS Carmem and BRS Violeta red wines elaborated from traditional and two alternative winemaking procedures: grape pre-drying and submerged cap. The wines contained higher concentration of acetates (ranging from 303 mg L-1 to 905 mg L-1) and ethyl and methyl esters (ranging from 138 mg L-1 to 415 mg L-1). The BRS Carmem wines were described as fruity due to the higher concentration of esters and BRS Violeta wines were described as vegetal mainly due to the higher concentration of terpenes and methoxyphenols. C6 alcohols also influenced the vegetal notes of BRS Violeta wines from traditional and submerged cap procedures and the pre-dried wines also presented a relevant jam note possibly due to the presence of 2-phenylethyl acetate. The changes in winemaking procedures can possibly lead to changes in the aromatic profile of red wines in a positive way, improving the wine aroma quality.

Experimental study of physical and rheological properties of grape juice using different temperatures and concentrations. Part II: Merlot.

The effect of the temperature and concentration on rheological behavior of Merlot juice concentrates was assessed using a rheometer over a wide range of temperature (1-66°C) and concentrations (13.6-45.0Brix) at shear rates of 0.84-212.1 1/s. The Ostwald-De Waele was the best rheological model fitted the data (R2=0.99967 and relative error=7.99%). The consistency levels were significantly reduced with the increase of temperature and increased with the increase of the concentrations, ranging from 0.1766 (13.6Brix at 66°C) to 19.1140Pa·sn (45.0Brix at 1°C). The flow behavior index presented no up or downward pattern when the temperatures were compared. The flow activation energy ranged from 13.95 (45.0Brix) to 24.88KJ/mol (21.0Brix) with a R2=0.9822 and 0.9812, respectively. Density and specific heat were influenced by both temperature and concentration; however, thermal conductivity was only influenced by concentration and temperature in two cases (13.6 and 29.0Brix). The data showed the potential use of Merlot juice concentrates as wine chaptalization agent in winemaking.

Experimental study of physical and rheological properties of grape juice using different temperatures and concentrations. Part I: Cabernet Sauvignon.

The effect of the temperature and concentration on rheological behavior of Cabernet Sauvignon juice concentrates was assessed using a rheometer over a wide range of temperature (1-66°C) and concentrations (13.6-45.0Brix) at shear rates of 0.84-212.1 1/s. The Ostwald-De Waele was the best rheological model fitted the data (R2=0.99957 and relative error=7.77%). The Cabernet Sauvignon juice concentrates presented a non-Newtonian pseudoplastic behavior (n<1). The consistency levels were significantly reduced with the increase of temperature and increased with the increase of the concentrations. The flow activation energy ranged from 28.87 (45.0Brix) to 38.05KJ/mol (37.0Brix) with a R2=0.9798 for both cases. Density and specific heat were influenced by both temperature and concentration; however, thermal conductivity was only influenced by concentration. The Cabernet Sauvignon juice concentrates will be useful as wine chaptalization agent in future studies.

Pre-drying and submerged cap winemaking: Effects on polyphenolic compounds and sensory descriptors. Part I: BRS Rúbea and BRS Cora.

In contrast to the most worldwide used grape varieties, wine production in Brazil is mainly devoted to the elaboration of table wines from American grapes and hybrids. These grapes show initial disadvantages such as low soluble solids content in their optimal stage of ripening and poor color quality. Based on this, the Brazilian Agency EMBRAPA Grape and Wine has developed BRS type cultivars in order to enhance the quality of the table wines. This study analyzed the phenolic composition and sensory profile of BRS Rúbea and BRS Cora red wines elaborated by traditional and two alternative winemaking technologies: grape pre-drying and submerged cap of chaptalized musts. Pre-dried wines presented low concentrations of anthocyanins/pyranoanthocyanins and flavonols, suggesting that they were partially degraded by the thermal treatment (60°C). These wines were described as bitter and full-bodied because of their higher flavan-3-ols content, suggesting that these compounds were not greatly influenced by thermal degradation. Submerged cap was described as persistent to the palate and with an intense violet hue due to its high anthocyanin and flavonol concentrations. The antioxidant capacity presented a weak relationship with the anthocyanins and stilbenes, but was intensely related to the % of galloylated flavan-3-ols.

Pre-drying and submerged cap winemaking: Effects on polyphenolic compounds and sensory descriptors. Part II: BRS Carmem and Bordô (Vitis labrusca L.).

Brazilian wine production is dominated by the use of American grape cultivars (Vitis labrusca L.) and their hybrids. In this context, this study analyzed the phenolic composition and sensory profile of Bordô and BRS Carmem red wines elaborated from traditional and two alternative winemaking technologies: grape pre-drying and submerged cap of chaptalized musts. Anthocyanins and pyranoanthocyanins apparently seemed to be affected by the thermal process (60°C), causing their degradation. In addition, the decrease of the concentration of these compounds could be suggested as a result of possible oxidation and hydrolysis reactions of anthocyanin 3-glucosides. Stilbenes were also affected by thermal degradation; however, flavan-3-ols and HCAD seemed to be less affected by the drying process. Submerged cap winemaking resulted in an increase of the anthocyanin and pyranoanthocyanin compounds due to the constant contact between the must and pomace during the alcoholic fermentation. The antioxidant capacity seemed not to be affected by thermal degradation, since the products of Maillard reaction also present antioxidant properties. Pre-dried wines were described as structured due to their higher flavan-3-ols content, and with high color intensity probably due to the formation of Maillard reaction products. The submerged cap wines presented an intense violet hue due to their high anthocyanin derivative concentrations and showed strong correlation with all other classes of the phenolic compounds.