Microwave-assisted maceration and stems addition in Bonarda grapes: Effects on wine chemical composition over two vintages.

Bonarda, the second red grape variety in Argentina, produces high yields per hectare generating, in several cases, low quality wines. Microwave-assisted extraction (MW) is a novel extraction technique for winemaking, widely applied in other foods. Stems addition (S) during vinification can be a sustainable technology for phenolic and aroma contribution without additional cost. Therefore, this study aimed to evaluate the combined effect of MW application with stem additions in different conditions, before fermentation, on the chemical composition of Bonarda wines. During two consecutive vintages (2018 and 2019), the experimental design consisted of ten treatments (two factors) by triplicate. Two maceration strategies (Factor 1) were applied [control (C), and microwaved-assisted extraction after grape crushing (MW; 2450 MHz, 7600 W, 45-50 °C)], combined with five stem-contact conditions (Factor 2) [control without stems (WS), 50% stems addition (S50), 50% stems addition + MW of the stems (S50MW; 2450 MHz, 7600 W, 60 °C), 100% stems addition (S100), 100% stems addition + MW (S100MW)]. Wines were analyzed for basic chemistry, phenolic composition and color parameters, polysaccharides, and aroma profiles. The 2018 wines showed higher pH and lower volatile acidity with stem additions and MW application in both matrices (grapes and stems). Stem additions increased tannin content by >55% (S100) and by >25% for the other treatments; while MW, mostly in the 2018 season, consistently improved phenolic extraction and polymeric pigments formation, enhancing wine color (greater saturation) and intensifying violet hue. The behavior observed in 2019 was similar, with a more marked effect of MW on wine color (C*ab and polymeric pigments). Likewise, combined strategies increased polysaccharides extraction and modified the volatile profile of wines. The reported results are promising and are considered the first advance in the knowledge of the impact of the proposed combined strategies on the chemical composition of red wines.

Comparative phenolic, chromatic, and sensory composition of five monovarietal wines processed with microwave technology.

The effect of MW technology (1,200 Watts for 10 min) on the chemical and sensory composition of five monovarietal wines with different phenolic composition was studied relative to untreated Control wines. MW improved polymeric pigment content by 30, 22 and 31% in Cabernet Sauvignon, Malbec, and Syrah wines, respectively, and anthocyanin extraction and non-tannin phenolics by 24% in Malbec and Syrah wines, respectively. In Nebbiolo and Pinot noir, MW had no effect on phenolics or chromatic characteristics. Anthocyanins in Nebbiolo wines were the lowest and their pigment profile was composed of 18% pyranoanthocyanins, but tannins were the highest, resulting in a tannin to anthocyanin ratio of 16. Pinot noir and Nebbiolo wines had comparable polymeric pigment content, despite dissimilar tannin to anthocyanin ratios, suggesting different mouthfeel characteristics in their respective wines. Conversely, wines of comparable tannin to anthocyanin produced wines of vastly different polymeric pigment content. MW-treated Cabernet Sauvignon wines showed an improved sensory profile.

Generation of a Non-Transgenic Genetically Improved Yeast Strain for Wine Production from Nitrogen-Deficient Musts.

The yeast Saccharomyces cerevisiae is the main species responsible for the process that involves the transformation of grape must into wine, with the initial nitrogen in the grape must being vital for it. One of the main problems in the wine industry is the deficiency of nitrogen sources in the grape must, leading to stuck or sluggish fermentations, and generating economic losses. In this scenario, an alternative is the isolation or generation of yeast strains with low nitrogen requirements for fermentation. In the present study, we carry out a genetic improvement program using as a base population a group of 70 strains isolated from winemaking environments mainly in Chile and Argentina (F0), making from it a first and second filial generation (F1 and F2, respectively) based in different families and hybrids. It was found that the trait under study has a high heritability, obtaining in the F2 population strains that consume a minor proportion of the nitrogen sources present in the must. Among these improved strains, strain "686" specially showed a marked drop in the nitrogen consumption, without losing fermentative performance, in synthetic grape must at laboratory level. When using this improved strain to produce wine from a natural grape must (supplemented and non-supplemented with ammonium) at pilot scale under wine cellar conditions, a similar fermentative capacity was obtained between this strain and a widely used commercial strain (EC1118). However, when fermented in a non-supplemented must, improved strain "686" showed the presence of a marked floral aroma absent for EC1118 strain, this difference being probably a direct consequence of its different pattern in amino acid consumption. The combination of the capacity of improved strain "686" to ferment without nitrogen addition and produce floral aromas may be of commercial interest for the wine industry.

Chemical, chromatic, and sensory attributes of 6 red wines produced with prefermentative cold soak.

Six red grape cultivars, Barbera D'Asti, Cabernet Sauvignon, Malbec, Merlot, Pinot Noir and Syrah, were produced with or without prefermentative cold soak (CS). Cold soak had no effect on the basic chemical composition of the wines. At pressing, CS wines were more saturated and with a higher red component than control wines. After 1 year of bottle aging, CS wines retained 22% more anthocyanins than control wines, but tannins and total phenolics remained unaffected. Both saturation and the red component of colour were slightly higher in CS wines. From a sensory standpoint, CS only enhanced colour intensity in Barbera D'Asti and Cabernet Sauvignon wines, whereas it diminished colour intensity in Pinot Noir. Cold soak had no effect on perceived aroma, bitterness, astringency, and body of the wines. Principal Component Analysis suggested that the outcome of CS is contingent upon the specific cultivar to which the CS technique is applied.