Well described, mostly due to a non-specific lipid transport protein (LTP) so likely to find various co-sensitivities.  Some will be wheat, barley, maize, rice, yeast etc positive but history likely to be suggestive.  Consider hops, metabisulphites.  Malting, filtration etc probably affects allergenicity.  Presence of alcohol may enhance absorption?  In the case below, maize LTP eventually identified but patient could eat polenta and popcorn!

But individual beers vary in their allergenicity, and skin prick testing can reveal types that are safe! Hoegaarden in this report – Allergy 2012:67;1186