Efficacy of Dimethyl Dicarbonate Against Yeasts Associated with Washington State Grapes and Wines

Abstract

Efficacies of dimethyl dicarbonate (DMDC) against yeasts associated with grapes and wines were evaluated. Addition of the legal limit of DMDC (200 mg/L) to grape musts initially inoculated with 102 cfu/mL (low population) or 105 cfu/mL (high population) of Candida californica, C. oleophila, Metschnikowia pulcherrima, Meyerozyma caribbica, Mey. guilliermondii, Saccharomyces cerevisiae or Wickerhamomyces anomalus resulted in declines of several logs. However, populations in excess of 106 cfu/mL were observed within days regardless of the initial inoculum. In contrast, culturability of Zygosaccharomyces bailii inoculated into grape must (low populations) or wine (low or high populations) did not recover after treatment with DMDC. In wines, low populations of Brettanomyces bruxellensis I1a or E1 declined after DMDC addition while culturability returned for F3 no matter the initial inoculum. Treatment of wines using commercial dosing equipment resulted in a gradual loss of culturability of Brettanomyces when inoculated at 104 cfu/mL while the concentrations of volatile phenols remained unchanged after >3 years of storage. Practical Applications Upon exposure to dimethyl dicarbonate (DMDC), initial loss of culturability was noted for several yeasts, most dramatically for Zygosaccharomyces bailii present in wine. Conversely, species of Candida, Metschnikowia, Meyerozyma, Saccharomyces and Wickerhamomyces examined achieved high populations in grape must within a few days after application. DMDC was generally effective against Brettanomyces under laboratory and commercial scale conditions but differences between responses were noted between strains. Although the additive initially reduced culturable populations, DMDC did not completely eradicate yeasts present in grape musts or wines and therefore may not provide long-term microbiological stability.