Should I be worried about wine if I have a gluten allergy?

Q: My wife has a gluten allergy. I understand that the glue in oak barrels is wheat-based. Is this a concern? I also have two cases of Conundrum 2006 and 2007. Do you know if they spent any time in oak? —Robert S., Richboro, Pa.

A: The subject of gluten in wine is often misunderstood. You are correct that using a wheat flour paste to seal a barrel’s croze—the groove in which the barrel’s head rests—is a trademark of traditional cooperage. But there are several details about this practice worth keeping in mind.

First of all, not all coopers use this paste anymore: “Wax substitutes have largely taken over because of ease of use and cleanliness,” notes Phil Burton, owner of Barrel Builders in Napa. Those traditional cooperages that do still employ the paste use extremely small amounts. Chris Hansen, general manager of Napa’s Seguin Moreau, says that his company applies only a few millimeters of this flour. Finished barrels, no matter their sealant, are rinsed and sanitized with sulfur dioxide before leaving the cooperage. Upon receiving barrels, winemakers typically inspect the interior with a flashlight, and any exposed wheat paste would show “a greenish haze,” according to Burton, which they would likely clean out before putting any wine in the barrel. In other words, the amount of this paste that ultimately penetrates the wine is probably negligible.

But just to make sure, Tricia Thompson, MS, RD, founder of GlutenFreeWatchdog.org, ran tests on wines that had seen considerable time in new oak. Her results indicated that these finished wines contained less than 5 and 10 parts per million gluten, respectively. (Products that contain less than 20 ppm qualify as gluten-free by the FDA’s standards, and 5 ppm is the lowest level at which gluten can be quantified.) “These are very, very, very small amounts,” warns Thompson. “There are so many areas where food can get cross-contaminated, but I really do not think that wine is an issue.”

Other than this flour sealant, the only potential source of gluten in wine is as a fining agent. But these gluten-based fining agents are very rarely used nowadays, and as with the paste, the amount that could appear in the finished wine is miniscule. A 2011 study in the Journal of Agricultural and Food Chemistry found that wines fined with a gluten-based agent ultimately contain either very little gluten or no gluten at all.

Absent any scientific confirmation that gluten has a significant presence in finished wine, we have only anecdotal evidence from people who believe that wine may upset them. Those who believe they are extremely sensitive to these small amounts of gluten can look for wines that have been aged in stainless steel and that are either unfined or fined with nongluten-based agents. Conundrum, a white blend produced by Caymus, does include components aged in oak. But until we see a convincing study proving otherwise, we would advise you and your wife not to worry too much about the presence of gluten in oak-aged wines.

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