Adaptation of a Simple Assay to Measure Tannins in Grapes and Wines

We have accomplished the objectives proposed for the 1996 season. We extracted seed tannin from Cabernet Sauvignon seeds and obtained enough to construct standard curves for several years. We will provide an aliquot this standard tannin preparation to those who wish to conduct similar assays. By assaying fractions from a seed tannin extract separated by HPLC, we determined that the microtiter assay detects the large polymeric tannins present in seed extracts. Simulated fining experiments showed that casein, gelatin and ovalbumin removed the tannin material detected by the assay. We determined that of the total amount of tannin detected by the plate-binding assay, 22%came from the skins and 78%came from the seeds. We have used the principal of the microtiter plate assay to develop a solution assay for tannin. This novel analysis is based on the observation that alkaline phosphatase activity, unlike many other enzymes, is not inhibited by tannin binding. The solution assay is less sensitive but shows less variation than the titer plate assay. The solution assay can be carried out using only a spectrophotometer and eliminates the need for a microtiter plate reader. Thus, the solution assay should prove useful in more winery laboratories than the plate assay.