Smoke taint

Over the last decade, big fires have affected viticultural areas all over the world, with climate change dramatically impacting their recurrence and importance. Besides the destruction of vineyards and wineries, the exposure of grapes to smoke leads to economic losses because of the occurrence of undesirable sensory characters in wine. These wines are perceived negatively by consumers who describe them as smoky, burnt, and ashy with medicinal notes and usually simply describe them as “smoke-tainted.”

What are smoke taint compounds?

During fires, a large diversity of free volatile phenols are present in the smokes, and these components are principally responsible for smoke taint. These components are directly absorbed by grapes and are partly metabolised to produce glycosides that do not have a smoky aroma. They are sometimes referred to as smoke taint precursors.

Smoke taint precursors can be cleaved during fermentation, but mainly over time in a barrel or bottle, releasing volatile phenols into the must or wine and thus allowing the smoky flavour to be detected. During the drinking of wine, these glycosides can also release volatile phenols in the mouth, which may contribute to the perception of smoke taint. Six different phenols are considered the main markers of smoke taint: guaiacol, 4-methylguaiacol, 4-methylsyringol, o-Cresol, p-Cresol, and m-Cresol.

Smoke taint glycosides represent a ticking bomb since they are progressively hydrolyzed during wine storage, thus progressively releasing the free and odorant smoky compounds.

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Progressive release of free and odorant smoky compounds in wine

What do we recommend for the management of smoke-exposed grapes?

Avoid the extraction of the off-flavour compounds

There are several steps that can be taken in the winery to minimise the sensory impact of smoke exposure.

The following suggestions have performed well for the good management of smoke-tainted grapes:

  • Hand harvest the grapes, excluding the leaves.
  • Keep fruit as cold as possible.
  • Press the whole cluster, doing minimal rotations of the press cycle, and separating press fractions.
  • Ferment in large volumes to ease the smoke taint to be integrated or masked.

Skin maceration should be as brief as possible. The use of pectolytic enzymes such as Rapidase Extra Press for white and rosé wine and Rapidase Fast Color for red wine at 2 g/100 kg of fruit will help to shorten maceration.

We recommend using appropriate yeast and bacteria (du Plessis, 2020, SASEV Conference) to increase fruitiness and to absorb or degrade some free compounds with Legacy VIN13 for white and rosé wine and Legacy NT112 for red wine.

Solution-aroma-wine-default-smoke-taint
Effect of yeast strain on the smoke taint total compounds (ug/L) after alcoholic fermentation on Chenin blanc and Merlot wines (sum of guaicol, 4-methylguaicol, 4-ethyphenol, and phenol) (adapted from du Plessis et al., 2021)

Additionally, sequential MLF appears to be a better choice than co-inoculation, meaning Anchor SOLO SELECT or the Maloferm cultures are the best options where smoke taint is evident or suspected.

Solution-aroma-wine-default-smoke-taint
Comparison of sequential and co-inoculation malolactic fermentation done with various bacteria cultures on the level of smoke taint compounds (guaiacol and 4-methylguaiacol) on Syrah wines, adapted from du Plessis et al., 2021

Solve the smoke smell problem and prevent the delayed occurrence of smoke taint.

As already mentioned, the compounds responsible for smoke taint can be found in bound and free forms, with a progressive release of the latter during storage and after bottling. This means that the elimination of both free and bound forms of components from the wine is required. Unfortunately, glycosylated compounds are very polar and hardly removed by classical removal techniques such as absorption on activated carbon or membrane techniques.

But since the structure of these compounds is very similar to the general structure of aroma glycoconjugates, the use of Rapidase Revelation Aroma appears to be very well adapted to the synergistic action of Extraferm D’tox, which adsorbs undesirable compounds in lees, or other techniques (activated carbon, membrane filtration).

In various studies, we have seen that Rapidase Revelation Aroma was able to release a significant number of volatile phenols from their bound forms (up to an 80% increase for smoked controls). There were also notable increases in “berries”, “floral/perfume,” and “prunes/jammy” attributes after enzyme treatment for all the wines. The next step using Extraferm D’tox showed promising results for the removal of volatile phenols after enzyme treatment, as the perception of fruitiness was not affected. It is noted that some winemakers preferred using carbon and reverse osmosis treatments instead of yeast hulls, with good results.

Therefore, the following protocol appears to be an efficient solution due to a dual effect: a direct effect due to the enzymatic release and subsequent removal of smoke taint compounds, and an indirect effect thanks to the increased fruitiness of the treated wine due to the release of beneficial aroma compounds.

  1. Add Rapidase Revelation Aroma at 5 g/hL during alcoholic fermentation to benefit from the highest temperature possible and to get a contact time of 6 to 8 weeks, enough to release glycosylated smoky compounds into free forms.
  1. Use Extraferm D’tox in two successive additions of 20 g/hL at 48-hour intervals (homogenise/stir, settle, and rack off between the two additions) to remove any undesirable free forms.

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