Survey of Analytical Methods and Winery Laboratory Proficiency

¹ Department of Viticulture and Enology, University of California, One Shields Avenue, Davis, CA 95616-8749, USA.

cebutzke{at}ucdavis.edu

Results of a survey of methods of analysis for five basic measurements of wine composition (pH, titratable acidity, volatile acidity, ethanol, and residual sugar) used in commercial winery laboratories are reported. A laboratory proficiency test was conducted with cooperating wineries for the same measurements. The proficiency test showed satisfactory results for the analysis of pH and ethanol in wine with coefficients of variation between wineries of 1.2% and 1.8%, respectively. Less than 20% of the wineries were proficient in measuring titratable acidity or volatile acidity. The range of reported volatile acidity concentrations varied more than two-fold. The analysis for residual sugar yielded unsatisfactory results, with a coefficient of variation of 140% and reported values ranging from 0.01 to 4.0 g/L. The results of this preliminary proficiency test suggested a need for improved laboratory quality management systems, especially with respect to analytical method standardization and validation, and for the establishment of proficiency testing program for American wineries. An "ASEV Winery Laboratory Quality Systems" CD-ROM was developed to guide wineries from the first steps of setting up a quality management system all the way to winery lab accreditation, and a continuous and frequent inter-laboratory proficiency testing scheme has been established.

Key words: wine analysis, winery laboratory, quality systems, proficiency testing, collaborative testing, method validation, ISO 17025, ISO Guide 43, wine quality

Submitted on October 13, 1998
Revised on March 9, 1999