Patrick G. Iland

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.

Charge equilibria and pKa of malvidin-3-glucoside by electrophoresis

Paper electrophoresis has been used over the pH range 1.2 to 10.4 to measure apparent pK(a) values for malvidin-3-O-glucoside of pK(a(1)) 1.76+/-0.07, pK(a(2)) 5.36+/-0.04, and pK(a(3)) 8.39+/-0.07. Using solvent partitioning between buffered aqueous solutions and n-octanol, several micro-pK(a) constants for malvidin-3-O-glucoside were also identified, highlighting the complex nature of malvidin-3-glucoside equilibria. As a nonspectrophotometric procedure, the charge-dependent electrophoretic mobility method provided independent information on the net charge and color of anthocyanin species at wine pH (ca. 3.6). At this pH, the color of malvidin-3-glucoside in red wines is consistent only with the uncharged quinonoidal base as a major colored component of the equilibria.

Relationships between grape and wine sensory attributes and compositional measures of cv. Shiraz

Relationships among sensory attributes, compositional measures, and wine quality of Shiraz grapes and wines were evaluated for two seasons, 2009 to 2010 and 2010 to 2011. The sensory profiles of berries and wines were evaluated by descriptive analysis and wine quality was assessed by an expert panel. In this study, berry sensory attributes alone were better predictors of wine sensory and compositional variables than the combination of berry sensory and compositional variables. Partial least squares regression analysis and Pearson’s correlation revealed a negative relationship between seed bitterness and wine savory spice flavor in both seasons. In 2011, pulp detachment from the skin correlated with wine sensory attributes such as rim color, fresh dark berry flavor, savory spice flavor, and wine quality score. Correlations among wine sensory attributes, wine pigmented polymers, and wine total tannins were identified in both seasons. These findings are important for grapegrowers and winemakers as they identify berry sensory attributes that may assist as objective measures in predicting final wine style and quality.

Shiraz (Vitis vinifera L.) Berry and Wine Sensory Profiles and Composition Are Modulated by Rootstocks

Sensory and compositional measures were conducted on berries and wines of Vitis vinifera L. cv Shiraz vines grown on own roots or grafted to three different rootstocks. The study was conducted in an experimental rootstock vineyard in the Barossa Valley, South Australia during two growing seasons (2009/2010 and 2010/2011). Wines produced from fruit from vines grown on their own roots were characterized by red berry aroma, whereas wines produced using grapes grown on vines grafted to either 110 Richter or Schwarzmann rootstocks had a darker rim and more intense body color, dark berry aroma, and red berry flavor, as well as more intense and coarser tannins. Juice and wines from rootstock treatments had higher levels of manganese, magnesium, and boron, while sodium level was higher in juice and wines produced from vines grown on their own roots. The majority of the acetate esters were higher in the wines made from vines on their own roots in both seasons. The highest wine quality scores were obtained by 110 Richter wines and the lowest by wines from own-roots treatment in both seasons. Differences in fruit exposure (moderated by rootstock) may affect fruit composition and sensory results and remains to be clarified. This study demonstrated that the use of rootstocks can have a positive effect on wine composition, sensory properties, and wine quality.