Abstract:
3-alkyl-2-methoxypyrazines (MPs) are grape- and insect-derived odor-active compounds
responsible for vegetative percepts that are detrimental to wine quality when elevated. This study
tested both the effect of closure/packaging types and light/temperature storage conditions on
MPs (isopropyl-, secbutyl-, and isobutyl-MP) in wine. An MP-emiched wine rapidly (after 140
hours) and significantly decreased in MP concentration after natural and synthetic cork contact
(immersion of closures in wine). This decrease was greatest with synthetic closures (70% - 89%
reduction) and secbutyl-MP. Subsequently storage trials tested the effects of commercial
closure/packaging options (natural cork, agglomerate cork, synthetic corks, screwcaps and
TetraPak® cartons) on MPs in MP-emiched Riesling and Cabernet Franc over 18 months.
Regardless of packaging, isobutyl-MP was the most altered from bottling. Notably, all MP levels
tended to decrease to the greatest extent in TetraPak® cartons (~34% for all MPs) and there was
evidence of contribution ofisoproyl- and secbutyl-MP from cork-based closures (i.e. ~30%
increase in secbutyl-MP after 6 months) or from an unidentified wine constituent. To test the
effects of various light/temperature conditions (light exposed at ambient temperature in three
different bottle hues, light excluded at ambient temperature and light excluded at a "cellar"
temperature (14°C)), MP-emiched Riesling and Cabernet Franc were also analyzed for MP
concentrations over 12 months. MPs did not vary consistently with light or temperature. Other
odorants and physico-chemical properties were tested in all wines during storage trials and
closely agree with previous literature. These results provide novel insights into MPs during
ageing, interactions with packaging and storage conditions, and assist in the selection of storage
conditions/packaging for optimal wine quality.
