Adams-Harbertson Protein Precipitation-Based Wine Tannin Method Found Invalid
Abstract:The poor precision of the Adams-Harbertson wine tannin assay which was proposed for commercial winemaking, thereby creating the real possibility of quality control problems, is documented. The method is a version of the Hagerman and Butler protein precipitation-based tannin method. An extensive invalidation of the assay results with luxury wine data shows that the assay cannot distinguish bottled wine with reasonable accuracy. Five laboratories used Adams-Harbertson to assay 9 replicates each, of 3 bottled wines (n 135) found in California supermarkets, with tannin concentrations of nominally 500 and 1000 ppm by high-performance liquid chromatography (HPLC). Reliability exceeded the 5 industry requirement by nominally 5 times (z-score based on 5 distribution). Coefficient of variation was 27, making the standard deviation range 54 for Pinot Noir, 34 for Merlot, and 44 for Cabernet Sauvignon. Validity exceeded the 100 requirement. Intralaboratory validity recovery was 5563. Interwinery validity was 71178 of the mean for Pinot Noir, 81144 for Merlot, and 83164 for Cabernet Sauvignon. Range as a function of the mean was 89 for Pinot Noir, 55 for Merlot, and 67 for Cabernet Sauvignon. Expect intermethod validity to be nominally 50, i.e., percent recovery to HPLC. These statistically significant errors were predicted by the literature. First-order error is related to the tannin-protein equilibrium constant (Ka), as suggested by the original author, Hagerman, and the protein equivalence point error as suggested by Silber. This does not obviate second-order errors for tannin-protein analytical chemistry. Winemakers using the measurements risk making wines that are relatively more tannic than the measurements report.
Document Type: Research Article
Affiliations: 1: LM Brooks Consulting, 979 Osos St, Suite C-1, San Luis Obispo, CA 93401. 2: Enologix, Inc., 461 Seventh St W., Suite 1, Sonoma, CA 95476. 3: University of California Santa Cruz, Santa Cruz, CA.
Publication date: 2008-09-01
- The Journal of AOAC INTERNATIONAL publishes refereed papers and reviews in the fields of chemical, biological and toxicological analytical chemistry for the purpose of showcasing the most precise, accurate and sensitive methods for analysis of foods, food additives, supplements and contaminants, cosmetics, drugs, toxins, hazardous substances, pesticides, feeds, fertilizers and the environment available at that point in time. The scope of the Journal includes unpublished original research describing new analytical methods, techniques and applications; improved approaches to sampling, both in the field and the laboratory; better methods of preparing samples for analysis; collaborative studies substantiating the performance of a given method; statistical techniques for evaluating data. The Journal will also publish other articles of general interest to its audience, e.g., technical communications; cautionary notes; comments on techniques, apparatus, and reagents.
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