Developing innovative phenolic analysis techniques
Background
This project provides Australian grape and wine producers with practical and informative methods and solutions to help them measure the tannin concentration in their grapes and wines and to help them better understand the implications of tannin. We have driven the development, adoption and application of new, commercially-applicable methods for tannin measurement in response to the wine sector’s need for objective indicators of grape and wine quality. The AWRI standardised methodology for quantifying tannins in grape and wine samples has been developed based on precipitation of tannin with methyl cellulose. This assay, known as the methyl cellulose precipitable (MCP) tannin assay is now fully optimised, validated and available to wine producers and researchers alike in 1 mL, 10 mL and high throughput (HTP) formats. A web accessible standard operating protocol (SOP) is available for the MCP tannin assay.
Progress
Development of rapid spectral grape and wine tannin measurement using the MCP tannin assay as reference method continued in collaboration with the Spectroscopy and Chemometrics team in the AWRI’s Industry Applications group. As a result, a very rapid UV-based predictive model for red wine tannin has also been developed. This allows prediction of tannin using simple, spectroscopic measurements.
In addition to assisting Australian producers with the measurement of tannin, we can now also provide information on what that tannin number ‘means’ within an Australian context. This significant opportunity stems from completion of our Australian grape and wine tannin survey and the development of a database that now allows investigation of significant tannin concentration variations between regions, vintages and varieties Furthermore, using allocation grading data from major sector partners, we have shown consistent positive correlations between red wine quality and tannin concentration. This proves that total wine tannin concentration can be used as one of the objective measures of quality in red wine (Smith et al. 2007).
A method comparison study was also completed that compared performance of the MCP tannin assay and the protein-based ‘Adams-Harbertson’ tannin assay. This showed that the two assays correlate very highly for 50% ethanol grape homogenate extracts (r2=0.96); highly for red wines (r2=0.80); and that the MCP tannin assay is significantly faster, simpler and cheaper to perform.
Highlights
- The AWRI standardised methodology for quantifying tannins in grape and wine samples has been optimised based on precipitation of tannin with methyl cellulose.
- A very rapid UV-based predictive model for red wine tannin has also been developed
- We have shown consistent positive correlations between red wine quality and tannin concentration.
Images:
Figure 1. Box plots showing Australian red wine tannin concentrations for Cabernet Sauvignon (CAS), Merlot (MER), Pinot Noir (PIN) and Shiraz (SHZ) (Source: AWRI Annual Report 2008, p. 19)
Figure 2. Wine tannin concentration vs red wine allocation grade as determined by a major Australian wine company over the 2004 to 2007 vintages (mean and SE) (Source: AWRI Annual Report 2008, p. 19)
Project leader: Dr Paul Smith
Project team members:
Publications:
975 Mercurio, M.D.; Dambergs, R.G.; Herderich, M.J.; Smith, P.A. High throughput analysis of red wine and grape phenolics-adaptation and validation of methyl cellulose precipitable tannin assay and modified Somers color assay to a rapid 96 well plate format. J. Agric. Food Chem. 55(12): 4651–4657; 2007 (click here to order).
971 Smith, P., Mercurio, M., Dambergs, R., Francis, L. and Herderich, M. (2007) Red grape and wine quality - the roles and relevance of tannin. Aust. N.Z. Wine Ind. J. 47-52 (click here to order).