The Effects of Bottle Aging on Smoke Taint Characteristics in Wine

With the recent wildfires in the Napa and Sonoma wine country, and now also those in Portugal and Spain, many are left wondering about the effects of the smoke on the wines coming from those regions.  First and foremost, it’s important to mention that at least for the

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Napa/Sonoma area, Napa winemaker Alison Crowe states that “more than 99 percent of California’s wine grapes were picked before the fire and probably more than 90 percent of Napa’s”, therefore the entire 2017 CA vintage is certainly not “ruined” as many early click-bait headlines would have you believe.

Smoke taint is a frequently studied phenomenon, since it affects wine regions throughout the globe and can have negative effects on sales. (In fact, I’ve covered some of this topic before.  Click here for links to articles).  Researchers are learning more and more about smoke taint every day, and with all this talk of smoke taint recently, I decided to look into what the latest studies have been examining.

It is currently understood that there are several compounds that influence our perception of smoke taint in wines, including (and possibly not limited to) guaiacols, cresols, and syringols. How much smoke from fires affect the perception of smoke taint in wine depends on a variety of factors, including when and for how long grapes were exposed to the smoke, as well as the specific variety or cultivar of grape that had been exposed.  Additionally, the winemaking technique used can influence the perception of smoke taint in wines, as well as the technique used to remove the offending compounds from the wine.

Studies have also shown how these volatile compounds are taken in by the grapevines, as well as how they change and are released in the grapes and wine over time.  In a super-rough description, the volatile compounds that are taken in by the grapevines are then glycosylated, which create these precursor compounds that are stable to a point until something or some process changes their structure to one of the compounds that are responsible for the perception of smoke taint in wine.

Aerial of the Sonoma County wildfires taken on Oct 14, 2017. Photo courtesy California National Guard (Flickr)

Some of these glycosylated compounds occur naturally in grapes, though for most grapes, these levels are considered to be very low (with the exception of Shiraz, which has 7 to 16-times more of these compounds than other grapes).

It is during the fermentation process that these glycosylated compounds can become hydrolyzed, which results in the release of the volatile compounds associated with smoke taint in wines.  It is important to note, however, that not all of these glycosylated compounds become hydrolyzed during fermentation, and that a significant chunk of them still exist in the glycosylated form even after fermentation and bottling is complete.

Since there appears to be a significant amount of these glycosylated compounds present in wines after bottling, a new study published in the Journal of Agricultural and Food Chemistry wanted to find out what happens to these compounds after bottling and subsequent bottle aging.  Specifically, the aim of the study was to examine the stability of smoke taint in wines during bottle aging.  As an aside, they also looked at another compound, benzyl mercaptan, to see if it could also be used as a marker for smoke taint in wine.

Brief Methods

The wines for this study were vinted in 2010 and 2011, from either control (no smoke treatment) grapes or grapes that were exposed to smoke for 1 hour 7 days after veraison. The grapes/wines used during the 2010 season were: Shiraz, Cabernet Sauvignon, Pinot Noir, Chardonnay, Sauvignon Blanc, and Pinot Gris. The grapes/wines used during the 2011 season were: Shiraz, Merlot, Chardonnay, and Sauvignon Blanc.

Small-lot fermentation techniques were employed, and with no malolactic fermentation. Wines were bottled and closed with screwcaps and subsequently cellared for 5 to 6 years.

Chemical and sensory analyses were performed immediately after bottling, as well as after 5-6 years of bottle aging.

Chemical analysis included: wine color, total phenolics, guiaicol glycoconjugates, guiaicol, 4-methylguiaicol, p-cresol, m-cresol, o-cresol, syringol, volatile phenols, and benzyl mercaptan.

A sensory panel of 11 trained researchers and students (with previous experience rating smoke taint wines) evaluated aroma, flavor, and mouthfeel of control and smoke-tainted wines.

Selected Results

  • Not surprising, the color and phenolic composition of all wines changed over time (as that’s what wine does when it ages…).
  • Color density changes of Shiraz and Pinot Noir wines were not significantly different between control and smoke-tainted wines over time.
  • Total phenolics in the 2010 Pinot Noir wines after bottle aging were significantly different at 0.4au for control wines and 2.0au for smoke-tainted wines, though the researchers noted this difference may not have been enough to be picked up by sensory analysis.
  • No significant differences in total phenolic content were observed after bottle aging in the 2010 white wines, though the control Sauvignon Blanc did have slightly higher levels than the smoke-tainted Sauvignon Blanc.
  • On the other hand, the 2011 wines were a different story for Sauvignon Blanc: the smoke-tainted wines had higher phenolic concentrations than the control wines both immediately after bottling and after bottle aging.
  • 2010: Guaiacol and 4-methylguaiacol increased (up to 4µL) after bottle aging for smoke-tainted wines as well as control Cabernet Sauvignon and Pinot Noir.
  • 2011: Guaiacol and 4-methylguaiacol increased (up to 6µL) after bottle aging for smoke-tainted wines as well as control Shiraz and Merlot wines.
  • 2010: Syringol increased substantially in smoke-tainted red (11-29µg/L) and white (3-7µg/L) wines, as well as control red (8-23µg/L) wines.
  • 2011: Syringol increased substantially in smoke-tainted red (14-23µg/L) and white (7-9µg/L) wines, as well as control red (8-17µg/L) wines.
  • 2010: Cresol levels decreased after bottle aging for smoke-tainted wines and control Shiraz and Cabernet Sauvignon wines, and it remained level for control Pinot Noir wines.
  • 2011: Cresol levels saw small increases (up to 4µg/L) after bottle aging
  • 2010 and 2011: None of the volatile phenols measured were found present in control white wines after bottle aging.
  • 2010: Guaiacol glycoconjugate levels were highest in Shiraz, then Cabernet Sauvignon and finally Pinot Gris. Smoke-tainted Chardonnay and Sauvignon Blanc wines showed similar levels.
  • 2010: There were no significant differences in guaiacol glycoconjugate levels immediately after bottling compared to 5-6 years of bottle aging for any wine.

Sensory Analysis:

  • 5 aroma and 6 palate characteristics were found to be significantly different between smoke-tainted and control wines after 5-6 years of bottle aging.
  • 2010: The smoke-tainted Shiraz and Pinot Gris were the most affected, with smoke and cold ash aromas, as well as smoky flavor and ashy aftertaste. The smoke-tainted Pinot Noir, Chardonnay, and Sauvignon Blanc were less affected, though still exhibited some less-intense smoke-related characteristics.
    • After bottle aging, the Pinot Gris still showed obvious smoke-related characteristics.
    • After bottle aging, smoke-related characteristics increased in smoke-tainted Pinot Noir and Sauvignon Blanc.
    • After bottle aging, loss of fruit character was not as noticeable in Shiraz and Chardonnay wines, thus smoke-related characteristics were not as noticeable either in these wines.
  • 2011: The smoke-tainted Shiraz, Merlot, and Chardonnay showed the most obvious smoke-related characteristics after bottling, while Sauvignon Blanc was more fruit-driven.
    • After bottle aging, the Merlot and Chardonnay still exhibited strong smoke-related characteristics.
    • After bottle aging, smoke-related characteristics were more noticeable in the Sauvignon Blanc than it had been at the time of bottling.
    • After bottle aging, the intensity of smoke-related characteristics decreased in the Shiraz.
  • 2010 and 2011: Control wines were (obviously) more fruit-driven, and retained this fruit character after 5-6 years of bottle aging.

The aside test to see if Benzyl mercaptan could be a marker for smoke taint

  • Benzyl mercaptan levels were higher in controls than smoke-tainted wines, so nope, it’s not a good marker for smoke taint.

Conclusions

Overall, this study highlighted how smoke taint affects wines over time in the bottle.  In general, as with all other compounds in wine, compounds linked to smoke taint characteristics also change over time in the bottle.  Interestingly, not all markers behaved the same way when comparing two different vintages.  While a couple of the markers behaved similarly (i.e. guaiacol, 4-methylguaiacol, syringol), other markers did not (i.e. total phenols, cresols). Even if you have the same smoke treatment, the wines aren’t necessarily going to respond in the same way from year to year.

What is also obvious from this study is that every grape/variety is different.  Some grapes appear to exhibit smoke-related characteristics in a more robust manner than others.  Additionally, over time, different wines will change in different ways in regard to smoke taint characteristics.  Specifically, in this study, the Pinot Gris wine seemed to show similar smoke-related characteristics right after bottling compared with 5-6 years of bottle aging.  On the

Random selection of Napa and Sonoma wines (NOT smoke-tainted). Copyright R.Yeamans-Irwin 2017.

other hand, in the 2010 vintage, smoke-related characteristics actually increased for Pinot Noir and Sauvignon Blanc.  In 2011, Sauvignon Blanc again showed an increase in smoke-related characteristics over time, while these characteristics seemingly decreased in the Shiraz.

So, what does this all mean?  Well, basically there is no one blanket answer here.  You can’t say that all wines will be affected by smoke the same way, just as you can’t say that over time the smoke-related characteristics of an affected wine will increase or decrease after bottle aging.  Not without more extensive research anyway.  What this study appears to be saying, however, is that as wines lose their fruit-driven character over time, the smoke-related characteristics become more prominent simply by the fact that the ratio of good-to-bad compounds has changed in their favor.  It is also very important to note than none of these wine underwent malolactic fermentation, so it’s not clear how bottle aging would affect smoke taint characteristics in those types of wine (of which there are many).

Interestingly, the precursors to some of these smoke-related characteristics—the guaiacol glycoconjugates—did not appear to change over time.  In other words, the wines showed similar levels of these glycoconjugates immediately after bottling compared to after 5 or 6 years of bottle aging.  This indicates that these compounds are relatively stable, so the aging process does not appear to interact with these compounds in such a way that they release new smoke-related volatile compounds in the wine over time.

Overall, this study suggests that if you have a smoke-tainted wine, overall the offending sensory characteristics will likely become more prominent over time, simply due to the fact that the wine naturally loses its fruit-forward characteristics, though exactly how offensive the wine becomes depends upon a multitude of factors including how much and for how long the smoke was applied, as well as the grape variety itself.

As one final, personal aside: please don’t let the recent wildfires in California (as well as Portugal and Spain) discourage you from purchasing the 2017 vintage when it comes out.  According to winemaker Alison Crowe, the “jury is out on what effects we’ll actually see [in Napa]. [It] could be very little, but we’re not assuming! We won’t know until we send the samples into ETS after [malolactic fermentation] is complete.” Odd are you’re going to end up with a perfectly lovely bottle of wine, and wine country will need your support more than ever to help increase sales and get back on their feet from this tragedy of both business and life.

Source:

Ristic, R., van der Hulst, L., Capone, D.L., and Wilkinson, K.L. 2017. Impact of bottle aging on smoke-tainted wines from different grape cultivars. Journal of Agricultural and Food Chemistry 65: 4146-4152.

1 comment for “The Effects of Bottle Aging on Smoke Taint Characteristics in Wine

  1. ckjyruth
    October 23, 2017 at 4:28 pm

    Fascinating. Very indepth information. Thank you for sharing.

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