Smoke Taint: Winemaking Implications for the Recent Fires

Sterilities: Why, When and How Many is Too Many?
December 18, 2015
IMPORTANT FEEDBACK – SMOKE TAINT 4-methyl guaicol and guaiacol results
March 14, 2016

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The recent fires are affecting many of our clients. We’d just like to say that we are thinking of you through these horrible times.

Smoke taint is an unfortunate reality in situations like this, but focussed research from around the world, specifically by the AWRI in Australia, has come up with some recommendations in dealing with smoke taint.

The background:

  • Wildfire smoke can contaminate vineyards, affecting grapes and wines, by leaving behind an aroma and taste described variously as smokey, burnt, ashtray etc.
  • The two main volatile aroma compounds that are measured in ‘smoke taint’ analysis are 4-methyl guaiacol and guaiacol. Smoke taint is not limited to these two compounds and the total smoke taint aroma is made up of more than 1000 other volatile aroma compounds.
  • Grapes are more susceptible the riper they become, being most susceptible after veraison.
  • The volatile aroma compounds enter the grapes directly through the skin and also, to a lesser degree, via the leaves.
  • The aroma compounds are found at highest concentrations closest to the skins.

White wine processing:

  • Minimize damage to fruit when harvesting. Hand harvesting is best.
  • Try to exclude leaves and other MOG.
  • Keep fruit at as cool temperatures as possible. Chill fruit when it enters the winery if possible.
  • Whole bunch press.
  • Heavier pressing will result in higher extraction of the smoke taint compounds. Separate press fractions earlier (400L).
  • Fine juice with carbon and/or bentonite.

Red wine processing:

  • Minimize damage to fruit when harvesting. Hand harvesting is best.
  • Try to exclude leaves and other MOG.
  • Do not do pre- or post-fermentation maceration. Try to reduce maceration time.
  • Ferment at lower temperatures – as low as possible.
  • Keep press fractions separate. Separate press fractions earlier (400L).
  • The addition of tannins have been found to potentially reduce smoke taint characters.

Analysing for smoke taint:

  • Meausre 4-methyl guaiacol and guaiacol on a fermentation trial (as described below), not on grapes.
  • The aroma threshold for 4-methyl guaiacol is 65µg/L in wine, and for guaiacol different threshold levels have been reported, ranging from 25µg/L (by the AWRI for levels in red wine) to 75-95µg/L from other sources.
  • The aroma compounds are often glycosylated in the grapes and not measureable in this state.
  • During fermentation the glycoside forms hydrolyse back to the volatile compounds. The volatile compounds should have reached a maximum after about three days of fermentation.
  • The AWRI recommends doing a mini-ferment to measure smoke taint potential. They recommend to harvest the trial grapes at 15-17deg Balling and ferment for 3 days aiming to imitate cellar processes as closely as possible.

At Vinlab, we would like to help our clients to get their wines through these fires as cleanly and efficiently as possible. We would like to offer clients a 25% discount on our ‘smoke taint’ panel for grapes affected by this years fires.