Monday, August 27, 2018

Estimates of cork taint from the Wine Spectator Napa office

The Wine Spectator magazine's Napa office tracked the number of apparently cork-tainted bottles in their tastings of California wines from 2005 to 2016, reporting their results at the beginning of the next year. There has been no report on the situation in 2017; and James Laube, who wrote the reports, has recently retired from regularly doing the California tastings (Wine Spectator announces changes in California wine reviewers). So, this could be an appropriate time to review their data.

A corked wine

Each year, all of the bottles tasted in the Napa office were assessed for "off" aromas. For bottles with corks, taint is usually caused by the presence of the chemical trichloroanisole (TCA) in the cork, but there are other potential sources of off smells. For example, the Cork Quality Council also lists 1-octen-3-ol, 1-octen-3-one, and guiacol.

Whatever the source, the data in the following graph refers to the "off" wines as a percentage only of those bottles with corks. Obviously, the data show that the percentage of tainted wines has improved through time.

Cork-tainted bottles in the Wine Spectator tastings of  California wines

Indeed, the trend looks impressively like cork quality is steadily improving. However, as I mentioned in a previous post (Drawing lines through a graph of points — what does this mean?), fitting a trend line to a graph can be a deceptive business. For example, the dashed pink lines in this next version of the graph highlight a different pattern — that tainted wines decreased between 2009 and 2010, but have otherwise remained relatively steady before and after then. Maybe something happened at that time?

Cork-tainted bottles in the Wine Spectator tastings of  California wines

Either way, the cork industry is usually reported to have a much lower estimate of cork failure than is shown in the graph above, typically 1-2 percent. This estimate was clearly not believable 10 years ago, and it is still half of that reported by the Wine Spectator, even now.

The cork manufacturers (mainly in Portugal) have been reported to be getting their act together, to improve the situation (eg. Taint misbehavin’: improving TCA testing methods to ensure cork quality). Improved testing may explain the apparent improvement between 2009 and 2010. The basic issue seems to be getting the cork wood clean, so that it can be turned into wine stoppers. Indeed, the industry is claiming that they will have eradicated TCA by the year 2020.

This raises the point as to why we use corks for wine bottles in the first place. Vidon Vineyard has this to say on the matter:
The main reason corks remain the predominant closure is tradition; change doesn’t come about easily in many fields. As long as one is willing to accept an occasional bad bottle of wine, corks are fine.
In any case, it seems clear that consumers often associate corks with high-quality wines (The effects of wine bottle closure type on perceived wine quality).

Vidon Vineyard's comments raise another important point:
A problem is that much of the time a cork-tainted wine isn’t recognized as such, but is passed off as “just not a good wine”, which means it’s the winemaker’s fault. And oftentimes a slightly tainted wine is consumed as “not too bad”, while if it could be tasted alongside an untainted wine with the same label, the reaction may have been “wow, this is great”!
Given that most wines are drunk within a few months of being released, the idea that we need corks in these particular wines seems to be ludicrous. Apart from anything else, untwisting a screw cap is so much easier!

On the other hand, we might also be concerned about the fate of the Cork Oaks (Quercus suber) themselves. These trees are owned and managed by farmers, who need to make a living from their land. If they can no longer make money from their cork trees, then those trees will be under threat of being replaced by some other crop. According to the Cork Quality Council, 37% of the cork forests are in Portugal (and 27% in Spain), where 50% of the cork production is centered (with 31% in Spain) — so, this is where the effect will be felt. In 2015, wine corks represented 72% of the Portugese cork industry's value, worth €644 million. This is not an inconsiderable industry, which will exert pressure to keep the Oaks.


  1. As a complement to James Laube's annual report, we can look to Wine Enthusiast magazine for the experience of one of their contributors who reviews wines from Washington and Idaho.

    "Yes, Cork Taint is Still a Problem"
    wine Enthusiast Magazine - Sean P. Sullivan (February 2, 2018)


    "Last year [2017], after tracking the more than 1,200 wines I sampled that used natural corks, 3.59% appeared to be cork-tainted, or were 'corked.' That’s a completely unacceptable percentage.

    "Moreover, while some believe cork taint is mainly a problem in inexpensive wines, my experience does not bear this out. In 2017, the average price of all cork-tainted bottles I sampled was just over $36. That’s not an inexpensive bottle of wine."

  2. From the Los Angeles Times "Food" Section
    (March 28, 2007, Page Unknown):

    "Simple solution for cork taint"


    By Corie Brown
    Staff Reporter

    "Corked wine is the ultimate wine disappointment, all the more crushing when the bottle in question is a costly, highly anticipated extravagance. One whiff of the aroma of old gym socks, the signature scent of trichloranisole (TCA), and the only option is to pour the bottle down the sink.

    "Or is it?

    "Mel Knox, a San Francisco-based oak-barrel broker who represents French cooper Taransaud, says there is an easy solution, particularly when the cork taint is relatively mild.

    "In a glass pitcher, wad up roughly a square foot of Saran Wrap or other polyethylene plastic wrap. Pour the tainted wine over the plastic wrap in the pitcher. Expose all of the wine to the plastic wrap by gently swirling the wine in the pitcher for five or 10 minutes. The more pronounced the taint, the longer the wine should be exposed to the plastic wrap. For stubborn cases, repeat the plastic soak with a fresh wad of wrap.

    "Pour out a small amount of wine to test the results and when the taint is gone, decant the wine into another container. Toss the plastic and enjoy the wine.

    "Polyethylene absorbs TCA like a sponge, says Brian Smith, president of Vinovation, a 'wine fix-it shop' that is experimenting with different plastic-filled cartridge filters that can be thrown into cork-tainted barrels or tanks to absorb TCA.

    "As offensive as cork taint is, from a health standpoint it's harmless. Cork taint derives its name from cork closures. The prime cause is a reaction between a mold found in cork crevices and chlorine-containing cleaning compounds used to clean the corks. Its presence also can be traced to wineries where phenolic wood preservatives come in contact with chlorine compounds. Once TCA infects a winery, it is difficult, if not impossible, to eradicate."

    The Wine Spectator has this advice:

    "If you’re going to start experimenting with this, pay attention to your plastic wrap’s ingredients. Most plastic wraps are made from LDPE, or low-density polyethylene, but some are made from polyvinyl chloride (PVC). Most folks seem to agree that PVC plastic wraps work better in this scenario."


  3. (Deleted and reposted to correct for a typo.)

    Wine bottle corks are both a renewable resource and a recyclable resource.

    Some retailers (such as Whole Foods Market) have collection bins in their wine departments to accept back used corks for recycling.

    Whereas other bottle closures are not actively recycled.

    From an environmental perspective, could cork finished bottles be considered more "environmentally friendly" than metallic screw caps?

    Discussed here:

    From the San Francisco Chronicle Online
    (May 19, 2011):

    "Better for environment: wine cork or screw-cap?"


    By Nancy Davis Kho

  4. I remember the 2004-5 period as terrible for cork quality. Some almost ditched corks altogether at that moment. How many customers we permanently lost is unknown. Better now but still unacceptable. If bad corks are "ok" as a trade off, then how about educating the consumer about how to detect taint? Right now all they now is that the "wine is no good" and drop the brand from future purchases.

  5. Let me add this article to the discussion.

    From Forbes magazine online
    (February 5, 2018):

    "Why Wine Corks Are On The Upswing"


    By Tom Mullen