Maria S. Mireles

Glucose, fructose and sucrose increase the solubility of protein–tannin complexes and at high concentration, glucose and sucrose interfere with bisulphite bleaching of wine pigments

Wines were modified with increasing sugar concentrations and decreasing tannin concentrations and analysed by a combination of protein precipitation and bisulphite bleaching. Increasing sugar concentration decreased the precipitation of tannin and protein-precipitable polymeric pigments (PPP). The use of a hydrogen bond disruptor (urea) to reduce protein-tannin and protein-pigment complex formation showed that the effect of sugar concentration occurred by increasing the solubility of the tannin-protein complex, not by interfering with protein-tannin complex formation. By increasing the solubility of pigment-protein complexes, non-protein-precipitable polymeric pigments (nPPP) appeared to increase. There was also an increase in total polymeric pigments at each tannin concentration with increasing glucose and sucrose concentration, indicating that sugar concentration might also affect bisulphite bleaching of wine pigments. While a significant effect of sugar concentration on tannin-protein complex solubility was observed, these effects were greatest at sugar concentrations far in excess of normal wine making conditions. Under normal wine making conditions, sugar concentration will have a negligible effect on protein-precipitable tannin, PPP and nPPP concentrations.

Improvement of BSA Tannin Precipitation Assay by Reformulation of Resuspension Buffer

Analysis of protein precipitable wine tannins has become more commonplace due to the simplicity of the method and the strong association between tannin content and perception of astringency. The traditional protein precipitation method for wine measures tannins and polymeric pigments using 5% w/v sodium dodecyl sulfate (SDS) and the alkaline buffer triethanolamine (TEA) pH 9.4 to dissolve the tannin-protein precipitate and support the colorimetric reaction with ferric chloride. However, this method results in a high background absorbance presumably due to the alkaline pH of the resuspension buffer, which has been shown to oxidize phenolics. Experimentation with several buffer formulations showed that pairing TEA with urea instead of SDS allowed formulation of buffers at lower pH. Urea-TEA buffers at pH 7 and 8 showed significantly lower background absorbance and drift over time as well as a significantly greater amount of tannin recovered. These trends in tannin content and iron reactive phenolics were maintained across a wide range of diluted samples (100–1200 mg/L catechin equivalents). Using a TEA-urea buffer at pH 7 or 8 may improve on previous methods of protein tannin precipitation by increasing yield of tannins from the wine and decreasing the background absorbance and drift.

Sensory Impact of Extended Maceration and Regulated Deficit Irrigation on Washington State Cabernet Sauvignon Wines

Irrigation practices such as regulated deficit irrigation (RDI) and winemaking practices such as extended maceration have been experimentally evaluated from a chemical perspective but their impacts on sensory composition and interactive effects merit scientific attention. This study evaluated the sensory impact of extended maceration applied to Cabernet Sauvignon grapes sourced from a vineyard subjected to four RDI treatments: replenishment of 100%, 70%, and 25% of full-vine crop evapotranspiration (ETc) from fruit set until veraison followed by 100% ETc until harvest (labeled 100% ETc, 70% ETc, and 25% ETc, respectively) and 25% ETc from fruit set to veraison followed by 100% ETc from veraison to harvest (labeled 25/100% ETc). Each RDI treatment was replicated four times (n = 4) and made into wine, with two replicates designated as controls (10 day skin contact) and two as extended maceration (30 day skin contact). Wines were evaluated by descriptive analysis with a trained panel (n = 15) and chemical and sensory data were correlated using canonical correlation analysis. Wine-perceived saturation and purple component ratings were highest in 25% ETc wines and were highly correlated with the concentration of flavonols, malvidin- and delphinidin-derivatives, and small polymeric pigments. Fruit-based aroma descriptors were highest in the 25/100% ETc and 70% ETc wines. Extended maceration increased perceived astringency and bitterness, which were in turn correlated with the concentration of flavan-3-ol and oligomeric proanthocyanidins. These results suggest that moderate RDI protocols such as 70% ETc and 25/100% ETc impact positively the fruity aroma component (black and red fruit), whereas extended maceration lowered fruity aromas, possibly due to the masking effect of the oxidized character perceived in these wines.

Influence of Fruit Maturity, Maceration Length, and Ethanol Amount on Chemical and Sensory Properties of Merlot Wines

Selected winemaking conditions were applied to fruit with ~20.3 and ~24.9 Brix over two seasons. Merlot grapes were harvested 33 (2011) and 34 (2012) days apart. At each harvest, half of the must was adjusted to emulate the other harvest’s soluble solids content to evaluate the effect of ethanol (EtOH) on phenolic extraction at different fruit maturities. Additionally, two maceration lengths of 10 days (control) and 30 days (extended maceration; EM) were tested. Control wines had significantly higher anthocyanin content, saturation, and red color component, whereas EM wines had enhanced tannin extraction from seeds, lower anthocyanin content, lower saturation, higher hue, and higher large polymeric pigment content. EtOH differences up to 2.7% (v/v) showed no significant effect on tannin and anthocyanin extraction, suggesting a minor role of this solvent under standard winemaking conditions. The later harvest date had a prevailing and positive effect on the sensory profile of the wines over winemaking factors such as maceration length and EtOH treatments. Wines from the early harvest fruit were defined by fresh vegetal character, acidity, and low color saturation. Wines from the late harvest fruit were defined by viscous mouthfeel, sweet taste, and fruit-derived aromas. Extended maceration shifted the sensory profile toward higher astringency, lighter and yellower color components, and cooked vegetal aromas. Chaptalization of early harvest fruit to 25 Brix shifted the sensory profile from cooked and fresh vegetable characters toward sweet taste, alcoholic, floral, chocolate/caramel attributes, astringency, and viscous mouthfeel. Overall, unripe fruit and the application of extended maceration had a negative impact on the sensory profile of the wines, whereas chaptalization of unripe fruit yielded wines with an improved sensory profile.

Cofermentation of Syrah with Viognier: Evolution of Color and Phenolics during Winemaking and Bottle Aging

Cofermentation of Syrah with additions of 5, 10, and 20% (by weight) of the white variety Viognier was followed during winemaking and up to 580 days postpressing to assess the effect of Viognier additions on the chromatic and phenolic composition of the wines. Additions of 10 and 20% Viognier lowered most of the chromatic parameters. At day 580, no differences were observed for tannins and iron reactive phenolics among the wines. Analysis of anthocyanins and flavonols uncovered no differences between 100% Syrah and 5% Viognier wines but the 20% Viognier wines had lower concentrations of anthocyanins and flavonols, suggesting possible dilution of these phenolics. These results suggest that additions of Viognier at the rates studied here neither improve the phenolic composition nor enhance the color stability of the final wines.