Viticultural management of grape tannin and anthocyanin levels to achieve desired wine quality specifications

Abstract

This project report summarises the results of over five years research on the extent of variation in winegrape tannins and the viticultural and environmental drivers of that variation.

Summary

This project, Viticultural management of grape tannin and anthocyanin levels to achieve desired wine quality specifications, was developed in response to the industry trend towards reward for quality based payment systems within the Australian wine sector. While a number of parameters have been used historically to assess grapes prior to harvest, the shift towards reward for quality had been based on relatively few parameters, most notably colour. As the limitations of colour as a key indicator of quality became apparent it was envisaged that the inclusion of additional parameters would ensure a more robust payment system.

In grapes and wine, the single biggest group of compounds that contribute to wine quality are phenolics. This group includes the coloured compounds (anthocyanins) as well as other diverse compounds. The largest class of phenolics are the condensed tannins, which are extracted from the grapes during winemaking and contribute to long term colour stability and mouthfeel in the wine. The grape and wine sector has long recognized this and several methods were developed for the assessment of tannins and phenolics. However, none of these found widespread acceptance, largely because it is difficult to interpret the data generated.

There are two main reasons for this. The methods fail to differentiate between important classes of phenolics and the body of knowledge on tannins and other phenolics in grapes is relatively limited. While some of the structures are known and many have been identified in grapes and wine, their distribution across varieties, relative abundance with respect to each other and the agronomic and environmental factors that influenced their accumulation is largely unknown.