Red Wine Phenolic Profiles
The Harbertson-Adams Assay was developed by Professor Doug Adams of the University of California at Davis and graduate student Dr. James Harbertson (now Associate Professor of Enology, Washington State University at Prosser). Through their joint effort they created an assay that brought together the sensory perception of a wine’s astringency and color with its quantities of phenolic materials present in the wine.
As opposed to measuring specific compounds in red wines, Drs. Adams and Harbertson desired to measure the total amount of phenolic materials that precipitate with (salivary) proteins knowing that these proteins react with many different molecular weight Tannins and Polymeric Pigment. They measured the amount of polymeric pigments as either Small Polymeric Pigment (SPP: five molecules in length or shorter) or Large Polymeric Pigment (LPP: over six molecules in length). And for a measure of the total amount of phenolic material present in a wine, the Harbertson-Adams assay uses ferric chloride to bind to a sample's phenolic materials. However, ferric chloride binds neither to polymeric pigments nor anthocyanins.
The families of red wine phenolic compounds measured by Wine X Ray consist of “Total Anthocyanins”, “Free Anthocyanins”, “Bound Anthocyanins©”, “Protein-Precipitable Tannins”, and “Total (iron-reactive) Phenolics”.
The specific standard operating procedure used is an extended version of the original Harbertson & Adams Tannin Assay; Harbertson et al, 2002 and 2003.
This assay relies on four fundamental characteristics of the behavior of wine phenolic compounds when they come into contact with salivary proteins, free sulfur dioxide, and ferric chloride. Namely, these underlying principles include (1) the pH behavior of anthocyanins in solution in the acidic region, (2) the ability of a solution of potassium metabisulfite to bleach anthocyanins, (3) the capability of proteins to form complexes with tannins and precipitate from solution, and (4) the reactivity of ferric chloride with phenolic compounds that possess vicinal dihydroxyl groups.
It turns out that in its classical form, the assay is neither timely nor practical for many wineries, small or large. Wine X Ray has run over twenty thousand wet chemistry analyses using a modified Harbertson-Adams Assay and recently an extended version of the modified assay. As with the goals of both Drs. Harbertson and Adams, the true power of the analysis would come with the creation of a predictive modeling system using an Ultra Violet-Visible Spectrum Spectrophotometer ('UV-Vis' for short). But the predictive UV-Vis model would only be as good as the fundamental wet chemistry data upon which the UV-Vis model was built. Wine X Ray has developed multiple models based on over 7,500 wet chemistry data points and has subsequently developed a predictive model using the UV-Vis data directly. The result is VESUVVIO which is a proprietary analytical system of Wine X Ray .