Methanol in wine

Abstract

The trace amount of methanol found in, wine depends on the grape content of the wine. Though small this amount could be used to determine how genuine the wine is. The methodology of tests for Methanol in Wine was assessed. Both commercially produced wines as well as home-made wines were sampled and analysed. The aim of the study was to determine whether the % methanol concentration vol./vol. differs significantly (statistically) between: (i.) Red wines and White wines; (ii.) Oaked wines and Unoaked wines - Red and White; (iii.) Low cost Table Wines, Red and White, produced by the two major wineries in Malta; (iv.) Commercially made Red wine and home-made Red wine; (v.) Home-Made wine produced traditionally and home-made wine produced using new scientific techniques; and (vi.) Wines produced from grapes of different harvest years. The effects on the methanol concentration of wine brought about by (i) wine dilution with water and (ii) grape skin contact during production were also investigated. The Official method laid down by AOAC Official Methods of Analysis (1990) 958.04, Methanol in Distilled Liquors, Chromotropic Colourimetric Method was used to determine the % methanol concentration vol./vol. of wines consumed locally. On validating the method, indeterminate errors were quantified at 0.0014% (good precision). Quantification of bias (determinate errors) gave a fixed bias of approximately -0. 001 % Methanol. This was attributed to losses during wine distillation. A relative bias of +4.52% of the actual methanol concentration in the wine was attributed to reagent interaction during methanol determination reactions. These two biases partly balanced each other, such that though not conclusive, the results obtained gave a strong indication of the real situation. Results obtained show that the difference in % Methanol concentration was not statistically significant between (i.) Oaked and Unoaked wines; (ii.) Home-Made wines produced using modern techniques and commercially produced quality wine; and (iii.) Wines produced from grapes of different harvests. On the other hand there was a statistically significant difference between the % Methanol concentration vol./vol. of (i) Red and White wines; (ii.) Low cost table wines - Red and White - produced by the two leading wineries in Malta; and (iii.) Home-Made wine produced in a traditional manner and that produced using modern techniques. A fixed amount of methanol could Methanol In Wine iv be produced from grapes and this did not depend on the grape variety but derives from winery processes. The % methanol derived from the skin was greater than that derived from the pulp of the grape provided due contact time with the skins was allowed. Dilution lowers the % Methanol concentration of wine and the method could be used to determine the extent of dilution. Spiteri l'vl. (199<3) found high sodium content in some locally produced wine. This may also be attributed to dilution and correlates with the author's findings on methanol content. Further investigation over a number of years may be required to confirm this hypothesis. The level of % MeOH in wine is not regulated by any local legislation. Not even by the E.U. Directives. Italian regulations allow a maximum limit of methanol of0.2% vol./vol for white wines and 0.25% vol./vol for red wines.