I've been doing a lot of reading/writing/researching on Cork Taint recently. It's a very interesting topic - an issue that revolutionized packaging development for the wine industry (and enhanced what the food industry knows as quality control). At some point, I'll have to do a lesson in our Wine Education Class Series (aka Wine Ed 411) on cork types and closures for all you winos out there, but for now, let us focus on the issue at hand: Cork Taint.
There's a controversial number out there related to the percentage of wines infected by corks. And every now and again, I always see people making horrendous statements in regards to that percentage, but with my experiences, I would say the level of cork taint infested wines is probably about 1% these days. Some reports say a lot higher (up to 8%), but with the great level of quality control that the cork companies and wineries now maintain, I'd say 1%. That means about 1 out of every 100 bottles of wine you drink is probably contaminated by cork taint. (Note: It's just not wine! Other spirits that use cork or wooden closures can also have cork taint. Trust me, it's gross once you realize it's there.)
The fascinating thing about cork taint (to me anyway) is that so many people are unaware of it. Ok, at extremely low levels (let's be generous and say less than 4 ppt), cork taint may not smell like anything to the average person. That's what is so interesting about cork taint: the primary compound (TCA) responsible for cork taint doesn't only have a particular aroma, at very low concentrations, it only masks or subdues the aroma of the wine itself. Therefore, a person would not be able to tell the wine is corked unless they had another bottle of the same exact wine (with a much more potent aroma).
The characteristic aroma of cork taint may be manifested by more than one compound. For those science geeks out there, this includes TCA (2,4,6-trichloroanisole), TBA (2,4,6-tribromoanisole), MIB (2-methyl-isoborneol), Geosmin, as well as TeCA (tetrachloroanisole), PCA (pentachloroanisole), and Guaiacol. Primarily, most people focus on TCA: the musty, moldy, wet cardboard, wet dog, or dank moist cellar smell. However, geosmin and MIB can have dirt, mud, or camphorous odors that are also associated with cork taint. Once identified, a corked bottle can completely ruin a wine for you!
The ultimate source of TCA in corks is truly unknown. There are some obvious guesses. We know that there is a mold or fungi that metabolizes chlorophenols (the precursor group to the chloroanisoles that have the cork taint odor) into chloroanisoles. However, the ultimate source of chlorophenols in the cork wood is somewhat unknown. Pesticides, fertilizers, wood treatment chemicals, etc. may contain chlorophenols, but again, the existence of the chloroanisole counterpart shows no correlation to the use of these chemicals. Additionally, it's difficult to identify how the molds are existing on corks from today's standards. Moisture levels on the corks are kept low in order to make sure there is no mold growth that would allow for a TCA contamination. There is some speculation that the mold or fungi hide in some of the natural corks' holes. But again, all corks are treated, primarily with hydrogen peroxide, to kill off any existing mold populations. (This reminds me - we should do a lesson on cork processing soon!)
Regardless of it's existence, at such low concentrations, TCA is not especially harmful to you. It just smells bad. Often when people first become familiar with cork taint, they are reminded of sea food. I found this is because some farm raised specifies (in particular - shrimp) can often be contaminated with Geosmin or MIB from water algae contaminates, therefore exuding the same aromas as cork taint itself!
Needless to say, there's nothing a winemaker can really do to ensure that the bottle you buy isn't corked. Sometimes it just happens. There's no perfect method to ensure 100% non-corked wines (well... other than buying wines using synthetic closures or screw caps). So what can you do if your wine smells like an old, musty basement? Kindly return it to the winery, or tell the sommelier at the restaurant, or the place of purchase. Typically, wineries are more than willing to replace a corked bottle.
If we could "scratch 'n sniff" on this wine blog, I would totally do that for you! But I cannot. That technology has not been created yet. However, I hope this lesson on Cork Taint opened some doors for the future wine connoisseurs out there...