2000/2001 Survey of Winery Laboratory Proficiency

Christian E. Butzke

Abstract

In 2000, the ASEV Technical Projects Committee's (TPC) Laboratory Proficiency Testing Guidance Committee established a continuous and frequent interlaboratory proficiency-testing scheme for the American wine industry. Results are reported for the first six rounds of the ASEV Laboratory Proficiency Testing Program for nine standard wine analyses performed in commercial winery laboratories. Proficiency was tested for analysis of ethanol, total and free sulfur dioxide, titratable acidity, volatile acidity, specific gravity, pH, residual sugar, and L-malic acid. The wineries were free to choose their methods of analysis, and the participants remained anonymous. Depending upon the assay, from 31 to 56 wineries participated, representing more than 90% of United States wine production capacity. The proficiency test showed satisfactory results in all rounds for the analysis of ethanol in wine with coefficients of variation among the wineries of 1.2 to 1.9%. The coefficients for titratable acidity (2.1 to 4.2%) and specific gravity (1.3 and 4.4% adjusted for table wine) were relatively low, but for the sulfite measurements, free (12 to 29%) and total (5.2 to 16%), they were considerably high. pH measurements on a logarithmic scale varied 5.7 to 9.1%. The combined relative errors for free SO₂ and pH were between 19 and 39%, impacting the presence of sufficient amounts of molecular SO₂ in the wines. Proficiency in the analysis of volatile acidity (6.7 to 25%) and malic acid (3.9 to 34%) was inadequate, as were the results for residual sugar (8 to 39%). The statistical results of the proficiency-testing program suggest a continuing need for improved laboratory quality-management systems. As a next step, wineries need to establish performance criteria for the different wine analyses that reflect the significance of their accuracy and precision for the quality and stability of wine.

Acknowledgments: The ASEV TPC Laboratory Proficiency Testing Guidance Committee (Glenn Andrade, Gordon Burns, Christian Butzke, Janice Byington, George Peterson, Ray Walker) acknowledges the wineries who participated in the ASEV Laboratory Proficiency Testing Program, especially those who provided the commercial wines for the first six test rounds (E. & J. Gallo Winery, Trinchero Family Estates, The Wine Group, Ironstone Vineyards, Bronco Wine Company, Delicato Vineyards). Furthermore, the committee recognizes Terry Lee, E. & J. Gallo Winery, for chairing the original TPC subcommittee Analytical Quality and for his industry leadership and vision. We thank Patricia Howe, formerly of Ascent Laboratory, and Sue Weeks, Bibber International, for their valuable advice and participation in the ASEV TPC Winery Interlab Group meetings and the Preharvest Wine and Grape Quality Air and Road Show 2001. We are grateful to Christopher Czyryca, Collaborative Testing Services, for his management of the program and the preparation of the survey reports, a summary and analysis of which is presented here.