Be very wary when you see Gluten Free Beer. I have just been warned by someone who ended up with a migraine followed by a raging headache after having a small glass of Green's Gluten Free Beer.
I have investigated further and found the product online and it has the following ingredient in it: de-glutenised barley malt.
Apparently, unlike Australia they are allowed in this country to call beer gluten free when it contains up to 20ppm gluten.
I came across this statement on yet another site relating to beers - perhaps others who use this forum may be able to elaborate on this subject .....
"The Barley based beers are technically Gluten Free, but they have hordeins, which function similar to gluten based gliadins, causing a response in Gluten sensitive or Celiacs." quoted from paleohacks.com site.
Sorry that this is a little disjointed but here is further information about just how high some gluten free alcoholic products may be: