The Thanksgiving holiday is nearly upon us. And I'd be willing to wager that wine will be on the menu. Whether you're giving a bottle of wine as a gift, serving wine as a host, or being offered wine as a guest, you'll almost certainly face the questions of whether or not to have a glass of wine, and which wine to have if you do.
Normally, there wouldn't be much to discuss from a gluten-free standpoint. It has long been understood that wine is gluten-free, largely because it is made from naturally gluten-free grapes. Case closed. But in recent months, I've been reading a surprising number of accounts who declare that - Warning! - not all wine is gluten-free. Such speculation has scared up quite the concern in the gluten-free community.
However, when reading these cautions, I was noticing a lot of hearsay and anecdotal stories, but not a lot of hard evidence. So, I decided to try and put the debate to rest, once and for all. Is wine safely gluten-free, or not, or somewhere in between?
The theoretical concern about wine and gluten comes in three primary flavors:
1. That some winemakers are adding gluten directly to their wine,
2. That some wines are aged in wood barrels that contain a wheat flour paste, and
3. That some wines are stored in barrels formerly used to age wheat-based whiskey.
Let's deal with concern #3 first, since it's the easiest to dispose of. It is grossly inaccurate, and unnecessarily causes worry. While it is true that some former wine barrels are used to age certain spirits, the reverse is not the case. (When's the last time you bought a bottle of wine whose tasting notes included "undertones of whiskey?") Much more importantly, however, whiskey and other spirits are aged AFTER distillation, which renders them gluten-free. Even if a wheat-based spirit was aged in oak barrels, and that barrel was later used to age wine, gluten never would have seen the inside of the barrel, because gluten wasn't in the whiskey.
Secondly, let's tackle concern #1, that some winemakers are (eek!) adding gluten to their wine. This bit of misinformation is at least partly accurate. The concern comes from the "fining" process for wine, a clarification process during which small solids, proteins, and undesirable tannins are removed from the wine. Typically, this is achieved through the addition of a fining agent, which has a higher specific gravity than the wine. As the fining agent passes down through the wine, ultimately settling on the bottom and discarded, it either binds to or reacts with the solids and proteins and tannins. A variety of agents - some more natural, others more synthetic - may be used, including gelatin and egg whites. Another much less common fining agent is in fact gluten. Its use increased slightly, especially in Europe, immediately following England's mad cow disease scare (since gelatin is made from the collagen of animal skin and bones, and winemakers were reluctant to use such an animal-based additive). However, it remains a less popular choice among winemakers.
But here's the thing, even for wines that use gluten as a fining agent. Winemakers use a fining agent not to add something to a wine, but rather to remove something from a wine. Gluten or any other fining agent is really just "passing through." To wit, at least two peer-reviewed journal articles have focused on studies that examine whether or not there's any residual gluten in wine from fining that might cause a problem for Celiacs or people with gluten intolerance. The short answer is, those wines are fine, too. The International Journal of Tissue Reactivity published "Evaluation of residual immunoreactivity in red and white wines clarified with gluten or gluten derivatives." The same journal also published "Evaluation...of residual antigenicity in gluten-treated wine." Both sets of researchers concluded the same thing - wine treated with gluten as a fining agent is safe for people on a gluten-free diet.
Which finally brings us to concern #2, that some wine barrels used to age wine contain a wheat flour paste. Like concern #1, this is also partly true. In the traditional method of barrel making (a profession and art known as coopering), the head that makes up the top or bottom of a barrel is set into a croze (a groove) cut into the staves at either end of the barrel. Traditionally, prior to setting the head, the croze was filled with a small amount of wheat flour paste as a sealant to prevent the barrel from leaking once it held liquid. Uh oh, you might think (quite reasonably).
But again, like the use of gluten for wine fining, only a small minority of winemakers use barrels that contain wheat flour paste. This is especially true of barrels made by artisanal coopers or those in France, who adhere more strongly to the old way of doing things. Most coopers these days have graduated from using wheat flour paste, and instead use a barrel sealing paraffin wax, which doesn't contain gluten. That still leaves open the possibility, however, that you might be unlucky enough to get a glass of wine from a wheat flour barrel, right?
Well, I couldn't find a single peer-reviewed article that studied the residual gluten content of wines stored in barrels that had wheat paste, so I posed the question to the experts at Cornell University's viticulture and enology program, in order to try and get to the bottom of things. They responded:
"...once the barrel is filled with water, the staves will swell and seal the barrel. The wheat paste provides only a temporary seal, and only a small portion of what is applied will still be in contact with the barrel contents... I would expect the amount of gluten on the inside of a 225 L barrel should be lower than that administered for red wine fining, both due to the small amount of exposed paste, and also because some of the paste would be lost prior to use. So, if there is any gluten, I predict it would be lower than results achieved with gluten fining trials."
And since gluten fining didn't cause problems, it seems reasonable to expect that barrels with wheat flour paste wouldn't either.
The bottom line is that there are plenty of things to react to in wine - yeast, tannins, alcohol, sulfites. But gluten isn't one of them. For my money, I'll continue to maintain that all wine is safely gluten-free. Just one more thing to be thankful for this Thanksgiving.
UPDATE: 4/18/11 - Earlier this month (April 2011) the Journal of Agricultural and Food Chemistry published "Immunochemical and mass spectrometry detection of residual proteins in gluten fined red wine," a peer-reviewed scientific study that raised new questions about the gluten-free status of certain wines. Researchers used two methods - mass spectrometry and immunochemical reactivity - to detect two forms of gluten that had been added to wine at various concentrations as a fining agent. Here's our analysis of the results:
Using mass spectrometry, researchers detected residual gluten in red wine down to an initial fining concentration of 1g/hL. That equates to 10ppm starting concentration. As we already know, most of the gluten added to a wine in the fining process leaves the wine. Only a small fraction remains. The 10ppm starting concentration is already half of the 20ppm international standard for gluten-free certification. The residual gluten in the wine would be even less. Thus, we conclude that mass spectrometry is a highly sensitive method of detection, but one that doesn't necessarily give rise for concern to the gluten-free community.
The immunochemical reactivity did raise eyebrows, however. Such reactivity is basically a mimic of our bodies' celiac reaction to gluten. If the study caused an immunochemical reaction, then we might become concerned that our bodies would react to the gluten too. Researchers did find immunoreactivity to one of the two forms of gluten at initial concentrations of 50, 150, and 300 g/hL of gluten. That equates to initial gluten concentrations of 500, 1500 and 3000ppm. Obviously, these starting concentrations are well above the 20ppm international gluten-free standard. Even accounting for the fact that most of the gluten will leave the wine, such high starting concentrations raise a red flag that ending concentrations might remain high enough to be unsafe for celiacs and other people who are highly sensitive to gluten. The immunoreactivity of the tests seemed to indicate just that.
This result led to a secondary question for me: The test concentrations of gluten as a fining agent were one thing, but how much gluten was typically added to wine in practice? Did real world conditions parallel the lab parameters? I searched the peer-reviewed literature to find out. One study from the Journal of Agricultural and Food Chemistry showed initial gluten concentrations of 6-18 g/hL when used as a fining agent. Another study from the Journal of the American Society for Enology and Viticulture showed initial gluten concentrations of 20-40 g/hL. Another example from Wine Chemistry and Biochemistry showed initial gluten concentrations of 20 g/hL. Finally, a fourth study showed initial gluten concentrations of 40 g/hL. (It's worth noting that 2 of these 4 studies also looked at immunoreactivity, and both came up negative, contradicting the results of the more recent study from April 2011.)
Based on these four peer-reviewed studies I surveyed, it would appear that real world initial concentrations of gluten used in wine fining range from 60-400ppm. The two studies that also examined immunoreactivity - which came back negative - were for initial gluten concentrations of 60-200ppm. It seems entirely reasonable to conclude that, once most of the gluten has been removed from the wine through the fining process, any residual gluten remaining in the wine would fall below the 20ppm threshold for gluten-free status. The two studies simultaneously examining immunoreactivity de facto confirmed this - they started with above-threshold levels of gluten, but after fining, did not cause a celiac-type immune response. I would apply this logic to all four studies. Thus, my personal conclusion is that real world applications of gluten used as a fining agent for wine don't use gluten in sufficient enough quantities to be a real concern for most of the gluten-free population.
The more recent study from April 2011 that did detect immunoreactivity to residual gluten did so for starting/initial gluten concentrations well above real world application rates. And yet, the fact that they did detect immunoreactivity does show that it could happen. Granted, the probability is very low. Remember: only a minority of wineries even use gluten as a fining agent, and more and more wineries are being transparent about the process, in recognition of the dietary restrictions and concerns of their customers. (Witness Kendall Jackson and Frey Vineyards.) Of the wineries that do use gluten as a fining agent, studies continue to suggest that those wines are safe for the gluten-free community to drink.
But if you consider yourself one of the super-sensitive members of the gluten-free community, the prospect of having a gluten reaction from wine is in the realm of possibility, even if that possibility is extremely small.