Wine is made from grapes and grapes are gluten free. Simple right?
Well yes... and no... but mostly yes
There are two potential places in the wine making process for gluten to sneek in: fining and aging.
Fining: Fining is the process of adding a fining agent to the wine to bind to larger unwanted particles and help them to precipitate to the bottom and be filtered out. Most common fining agents are isinglass (obtained from fish), bentonite clay or egg whites. Some years ago, gluten was investigated as a fining agent. I've not been able to find any examples of it actually being used in the fining process.1 I've seen a number of sources and caution about fining agents, but I suspect that it's a case of broken telephone. Someone found out that gluten was being studied, assumed it was being used and then multiple sources started quoting that as fact.
Aging: Some wines, mostly reds but also chardonnay, are aged in oak barrels. Sometimes wheat paste is used as a sealer for the barrels although most use waxes and paraffins. If a wheat paste is used, the barrel is washed, scrapped and sanitized so that it's unlikely any traceable amounts of gluten would come through to the final product. 2
Bottom Line: Wine in general is safe. The exceptions are few and far between. I rarely even check specific brands anymore and I'm pretty diligent about my gluten sleuthing.
I noticed a long time ago that red wine causes me trouble. I get terrible headaches that mimic a colossal hangover after just one or two glasses. As a result I tend to avoid red wine, which is really kind of tragic. I get a similar reaction to Chardonnay with the additional pleasure of severe acid re flux.
The common denominator between many red wines and Chardonnay is the oak. That leads me back to wondering if the gluten in the oak barrel concern might be work taking seriously. Yet I'm fairly certain it's not a gluten reaction as I know what that feels like and this is quite different.
It's been suggested to me that tannins in wine may be the culprit. Tannins come from contact with the skin so are more prevalent in red wine. They also come from contact with oak, which may explain the Chardonnay affect. However I have no issue with tea or coffee and they both contain tannins. So it's a bit of a mystery. If you have any ideas or a similar experience I'd love to hear from you.