RT Journal Article
SR Electronic
T1 A Review of Thirteen Years of CTS Winery Laboratory Collaborative Data
JF American Journal of Enology and Viticulture
JO Am. J. Enol. Vitic.
FD American Society for Enology and Viticulture
SP ajev.2015.14119
DO 10.5344/ajev.2015.14119
A1 Patricia A. Howe
A1 Susan E. Ebeler
A1 Gavin L. Sacks
YR 2015
UL http://www.ajevonline.org/content/early/2015/04/24/ajev.2015.14119.abstract
AB Data from thirteen years (78 wines) of wine industry laboratory proficiency testing were reviewed. After outlier removal, within-laboratory precision (repeatability) and across-laboratory precision (reproducibility) were determined for measurements of alcohol, titratable acidity, volatile acidity, total SO2, free SO2, malic acid, specific gravity, pH, residual sugar, glucose plus fructose, and absorbance at 420 and 520 nm. Reproducibility was 3.6 to 57.8 times higher than repeatability. Reproducibility was evaluated with Horwitz Ratios (HorRat); only alcohol, titratable acid, and total SO2 had acceptable values (mean HorRat < 2). Measurement z scores demonstrated non-normal distributions, particularly specific gravity, likely due to confounding with density. Reproducibility did not vary significantly over the time period studied, with exceptions: imprecision of ethanol measurements decreased (improved) by 0.0084% v/v per year, while the imprecision of titratable acidity, pH and malic acid measurements increased by 0.0089 g/L as tartaric, 0.0008 pH units, and 0.13 g/L per year, respectively. Reproducibility and repeatability imprecision generally increased with analyte concentration, with notable exceptions of alcohol (both), volatile acidity (reproducibility), and total SO2 (repeatability). The methods or instruments for alcohol, titratable acidity, free and total SO2, and volatile acidity changed significantly over the time period. Significant differences were observed among techniques for many analytes, which can be rationalized by attribution to well-known matrix effects manageable in a properly run method; e.g. higher apparent concentrations of alcohol by boiling point methods in high sugar matrices. Evaluation of method accuracy was not possible due to a lack of wine reference materials with known true values. Results demonstrate the need for industry-wide improvement in analytical performance for some assays, and the potential benefit of adopting criteria guidelines for method performance.