I.L. Francis

Characterizing the astringency of red wine: a case study

Red table wines of quality are characterized by pleasing and complex mouth-feel sensations, the most important of these being astringency. While a comprehensive set of terms has been developed over time to describe the flavor of red wines, an appropriate vocabulary describing the astringent sensations produced by these wines is not well defined. This paper presents a structured vocabulary derived by a panel of experienced wine tasters that can be used to describe the astringent sub-qualities of red wines. Multidimensional scaling of sorting data showed that an experienced panel and a group of skilled red wine-makers had similar interpretations of the relationships among the astringency terms. A tasting panel was successfully trained to identify and consistently rate the intensity of the astringent sub-qualities encountered in a set of one year old Shiraz wines. A novel approach of using finger touch standards to represent the astringent sensations experienced in the mouth was utilized.

Prediction of colour and pH in grapes using a diode array spectrophotometer (400–1100 nm)

One hundred and twenty thawed samples of homogenised and whole frozen grape berries were analysed using a diode array spectrophotometer (400–1100 nm) (CORONA 45VISNIR, Carl Zeiss, Germany). The spectra and the analytical data were used to develop partial least squares calibrations to predict colour and pH in both presentation modes to the instrument. The visible (vis: 400–700 nm), near infrared (NIR: 700–1100 nm) and vis + NIR (400–1100 nm) regions were used to perform the calibrations. Cross validation models for colour and pH on homogenised samples gave a coefficient of determination in validation (R2val) and the root mean square error of cross-validation (RMSECV) of 0.92 and 0.07 mg g−1 for colour, and 0.90 and 0.04 for pH, respectively, using the vis region. Presentation of intact whole grape berries gave R2val and RMSECV values of 0.50 and 0.14 mg g−1 for colour, 0.60 and 0.08 for pH using the NIR region. It was concluded that homogenised samples gave the best calibration statistics. More research needs to be done to improve calibration on whole samples if the technology is to be used for rapid analysis for either on-farm or on-harvester applications.

Contribution of several volatile phenols and their glycoconjugates to smoke-related sensory properties of red wine.

Guaiacol and 4-methylguaiacol are well-known as contributors to the flavor of wines made from smoke-affected grapes, but there are other volatile phenols commonly found in smoke from forest fires that are also potentially important. The relationships between the concentration of a range of volatile phenols and their glycoconjugates with the sensory characteristics of wines and model wines were investigated. Modeling of the attribute ratings from a sensory descriptive analysis of smoke-affected wines with their chemical composition indicated the concentrations of guaiacol, o-cresol, m-cresol, and p-cresol were related to smoky attributes. The best-estimate odor thresholds of these compounds were determined in red wine, together with the flavor threshold of guaiacol. Guaiacol β-D-glucoside and m-cresol β-D-glucoside in model wine were found to give rise to a smoky/ashy flavor in-mouth, and the respective free volatiles were released. The study indicated that a combination of volatile phenols and their glycosides produces an undesirable smoke flavor in affected wines. The observation of flavor generation from nonvolatile glycoconjugates in-mouth has potentially important implications.

The role of potent thiols in Chardonnay wine aroma

Background and Aims Polyfunctional thiols are key aroma compounds in many Sauvignon Blanc wines, but their role in other white cultivars is not clear. Methods and Results A survey of 106 commercial Australian Chardonnay wines found a high concentration of 3-mercaptohexan-1-ol, 3-mercaptohexyl acetate, benzyl mercaptan and 4-mercapto-4-methylpentan-2-one, with nearly all wines having a concentration of all compounds well above their reported sensory detection threshold, and some having a concentration comparable to that found in highly fruity Sauvignon Blanc wines. Wines were made on a research scale from a set of Chardonnay juices sourced from 16 vineyards across Australia. Sensory descriptive analysis combined with quantitative aroma volatile data revealed that several aroma and flavour attributes were related to the concentration of the thiols. Conclusions This study provided evidence that substantial flavour in Chardonnay can be contributed by these thiols. Additionally, consumer acceptance data showed that wines with a higher thiol concentration were liked by most consumers. Significance of the Study This study revealed the importance of polyfunctional thiols in Chardonnay wine.

More hawthorn and less dried longan: the role of information and taste on red wine consumer preferences in China

Background and Aims This study uses sensory evaluation techniques to test the relative influence of country of origin, price and sensory attributes on consumer preferences in a new wine market. Methods and Results Red wines from France, Australia and China were tasted by Chinese consumers under blind or informed conditions. Sensory descriptive data were collected from a Chinese-trained panel. A higher price and being from France were the strongest predictors of informed liking, while being from China had a negative influence for most of the consumers. Some consistency was found in sensory preferences between blind and informed tastings, indicating that sensory aspects of the wine are important. Well-liked wines were generally high in fermented bean curd, hawthorn and woody, and low in salty and dried longan attributes. Conclusions Price and country of origin generally are more important than the sensory aspects, however, a significant proportion of consumers are less concerned about origin and price and were more influenced by the sensory characteristics. Significance of the Study Even in a new wine market, producers benefit from understanding consumer reactions to the sensory properties of wines and to extrinsic attributes in order to successfully meet consumer expectations.