Macrowine 2021
IVES 9 IVES Conference Series 9 The evaluation of tannin activity in south african red wines

The evaluation of tannin activity in south african red wines

Abstract

Astringency is an important red wine quality attribute, which can be measured both chemically and sensorially. The use of tannin activity shows potential as a valuable chemical measurement in understanding red wine mouthfeel properties such as astringency and bitterness, which is also affected by tannin structural factors, in addition to matrix effects. Tannin activity is defined as the enthalpy of interaction between tannins and a hydrophobic surface. Studies involving tannin activity have been performed since the early 2010’s, but chemosensory studies used to evaluate how structure-activity relationships change across multiple, consecutive vintages are limited. The aim of this study is to investigate how tannin activity may be linked to red wine mouthfeel, and how all these variables may change according to wine age.

The effect of wine vintage on tannin activity was investigated in red wine extracts isolated from 16 Pinotage wines from a well-known producer (2003-2018) using Sephadex LH-20 chromatography. Approximately 17-18 polymeric fractions were obtained per wine, and furtherly grouped into four sub-fractions of various classes: low, medium, high, and bulk, giving 64 unique extract samples. Bulk samples represent a combination of the three other obtained fractions. Pooled extracts were grouped to obtain samples of variable but increasing molecular mass, which may each reflect differences in total phenolic and tannin content, and degree of polymerization, parameters previously shown to affect tannin activity. Retention thermodynamics were used to calculate activity values by utilising reverse-phase liquid chromatography (RPLC) on a polystyrene divinylbenzene column. Other complementary tannin-based techniques – to investigate structure-activity-concentration relationships – were also performed by obtaining chemical information based on subunit size and composition (by phloroglucinolysis), and total tannin content (by MCP and RPLC). Sensory analysis was performed by an expert panel to evaluate sweetness, acidity, body, complexity, astringency and bitterness. Younger wines’ polymeric profiles may be characterized by lower tannin activities and content, smaller degrees of polymerization and therefore an increased perception of bitterness, with higher activities and tannin concentrations in aged wine due to polymerization reactions – this may also explain why aged wines are perceived as more astringent than younger wines (Barak & Kennedy, 2013; Watrelot et al., 2016; Yacco et al., 2016). Furthermore, tannin activity values may plateau and show a decrease in older wines as tannin structural changes may lead to decreased tannin-protein interactions. Wine vintage may show a similar effect across all weight classes except in bulk wine fractions. These measurements could serve to establish how chemical measurements are linked to the sensory outcomes of this study and ultimately how mouthfeel perception is modulated according to wine vintage.

DOI:

Publication date: September 24, 2021

Issue: Macrowine 2021

Type: Article

Authors

Brannigan Du Preez , Jose Luis Aleixandre-Tudo

Stellenbosch University: South African Grape and Wine Research Institute (SAGWRI), Department of Viticulture and Oenology, Polytechnic University of Valencia, Research Institute of Food Engineering for Development; Stellenbosch University, South African Grape and Wine Research Institute (SAGWRI), Department of Viticulture and Oenology

Contact the author

Keywords

tannin activity; vintage; astringency; pinotage

Citation

Related articles…

Short-term canopy strategies to enhance grapevine adaptation to climate change

Context and purpose of the study – Viticulture faces significant challenges due to climate change, with increased frequency of extreme weather events impacting grapevine growth, grape quality, and wine production.

Read More

Agroclimatic zonation for vine growing in Maranhão State, Brazil

es indices agroclimatiques concernant le bilan hydrique et la température moyenne de l’air, ont été utilisés pour la caractérisation des zones avec différentes aptitudes pour la viticulture de vin (Vitis vinifera L.) dans l’état du Maranhão, Brésil.

Read More

MOUSY OFF-FLAVOURS IN WINES: UNVEILING THE MICROORGANISMS BEHIND IT

Taints and off-flavours are one of the major concerns in the wine industry and even if the issues provoked by them are harmless, they can still have a negative impact on the quality or on the visual perception of the consumer. Nowadays, the frequency of occurrence of mousy off-flavours in wines has increased.
The reasons behind this could be the significant decrease in sulphur dioxide addition during processing, the increase in pH or even the trend for spontaneous fermentation in wine. This off-flavour is associated with Brettanomyces bruxellensis or some lactic acid bacteria metabolisms.

Read More

Soil and nutritional survey of Greek vineyards from the prefecture of Macedonia, Northern Greece, and from the island of Santorini

Vitis vinifera L. is one of the most important cultures for the soil and
climate conditions of Northern Greece and Santorini. However, very little information is provided with regard to its nutritional requirements and critical levels of nutrient deficiencies and toxicities. The aim of this study was to provide an integrated nutritional survey for the Greek conditions of wine and table varieties.

Read More

The sensory profile of astringency: application on Sangiovese wines

One of the main sensory characteristics of red wine is astringency, which can be defined as drying, puckering and roughing of the oral cavity after the exposure to tannin-rich wines. Tannins are the main responsible for the intensity of the sensation as well for the qualitative aspects of astringency. However, the total intensity of the sensation is not sufficient to fully characterize red wine astringency. Thirty-three different subqualities (Gawel et al. 2001) had been generated to describe the complexity of this multi perceptual phenomenon, which includes both tastes, tactile, and flavor sensations. So, how to feel tannins during tasting? In this study, we used a sensory method that combine the training for astringency subqualities with touch-standards and the CATA questions, usually applied in consumer science, to evaluate the astringency subqualities of different typologies of Sangiovese: commercial and experimental wines. Sangiovese wine represents a good model for the study of astringency because it is generally characterized by a high content of low and high molecular weight proantocyanidins. Commercial wines differed for percentage of Sangiovese (80-100 %) grapes used in winemaking and for designation (Toscana TS, Chianti Classico CH, Chianti Riserva CR, Morellino di Scansano MS). The astringency profile of wines changed as the percentage of Sangiovese increased. Positive subqualities as velvet, soft, mouthcoat, and rich highly characterized the Sangiovese wine belonging to TS and CR designations. Moreover, the astringency subqualities related to blending or wood aging, represented the drivers of quality of commercial Sangiovese wines.

Read More