Astringency in red wines

Adams, Douglas. O., Harbertson, James. F., & Reid, Matthew. S. (2004, November/December). Assessing red wine astringency. Practical Winery and Vineyard, pp. 45-50.

This American paper was based on the results of tannin measurements carried out on 455 commercial red wines.

The authors point out that astringency is a tactile sensation caused by tannins and the effect of pH, viscosity, alcohol level and ionic strength within the wine. This is analogous to the sensation of sweetness in wine where the sugar levels are affected by such factors as acid levels and the other components that contribute to taste and texture.

There are several different methods for measuring tannins in wine. Depending upon the method used quite different results will be obtained. Assays based on protein precipitation are thought to use the same mechanisms as those that are responsible for astringency. The perception of astringency largely results from the tannins in the wine precipitating the proteins in saliva that are responsible for lubricating the inside of the mouth.

Unsurprisingly wines of different varieties had quite different levels of tannins based on protein precipitation methods. There were considerable differences both within varieties and between different varieties. In the trial on which this paper was based Cabernet Sauvignon had the highest levels followed by Zinfandel, Syrah and Pinot Noir. The Syrah and Pinot Noir, had similar levels of tannins, and these were considerably lower than the other two varieties. However when colour determinations were carried out the Syrah's wines typically had much more colour than the Pinot Noir wines.

When measurements of total phenolics were performed by the Folin-Ciocalteau (FC) method the results obtained did not show the same large range of tannin levels as when samples were tested using the protein precipitation method. The Folin-Ciocalteau (FC) method measures total phenolics levels that include anthocyanins, monomeric flavan-3-ols, flavonols and hydroxyycinnamates. These groups of tannins contribute very little to the astringency even though some of them may contribute to the bitterness in wine

In this trial the tannin level in one Cabernet Sauvignon wine was measured at bottling and again three years later. The tannin levels were similar in both samples although the aged sample had a lower level of astringency. Apparently factors other than the tannin levels were responsible for the different perception of astringency.

Additional work is required to exam the factors responsible for the qualitative as well as quanitative levels of astringency. These different levels of astringency are not solely due to the tannin levels present in the wine.

Reviewed by Nick Sage - December 2004