Adams-Harbertson protein precipitation-based wine tannin method found invalid.
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 55-63%. Interwinery validity was 71-178% of the mean for Pinot Noir, 81-144% for Merlot, and 83-164% 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.
Brooks
Larry
L
LM Brooks Consulting, 979 Osos St, Suite C-l, San Luis Obispo, CA 93401, USA. lmbrooks@pacbell.net
McCloskey
Leo
L
McKesson
Doug
D
Sylvan
Marshall
M
D002851:Chromatography, High Pressure Liquid; D007202:Indicators and Reagents; D011506:Proteins / Q000737:chemistry*; D015203:Reproducibility of Results; D013634:Tannins / Q000032:analysis*; D014920:Wine / Q000032:analysis*
D007202:Indicators and Reagents; D011506:Proteins; D013634:Tannins