While not beer I have some experience doing this with the family apfelwein. It does change the flavor of the wine from an apfelwein to a much more fresh apple taste (to me just like you bit into one of the apples) with a decent "burn" on the end.
I have discovered that when doing this it is easy to freeze the 1st time but becomes exponentially more and more difficult. I fill a large wine bottle 1/2 full, lay it down in the freezer and let it freeze solid. (This is normally done overnight.) Then let the contents drain into a large glass mug on the counter until is looks like a snow cone or mostly ice in the bottle. Another poster suggested 2 hours and this seems about right.
After the 1st time the solution should be near 25% or more making it near impossible to concentrate it again at freezer temps. I tried it though and used a funnel with cheese cloth to filter out the ice as it was mostly liquid, the ice at this point looked like it was holding quite a bit of color and was small shavings that would melt fast.
While the above works for wine I would not try this process with beer due to oxidation. You would defiantly want to slightly freeze the beer then rack it vs. let gravity drip it into another container.
IMO this can be expensive AND time prohibitive if using your own brew. Taking into consideration the time it takes to make apfelwein (my families is over 1 year) then you concentrate a batch, I think mom would "tan my back side" if she knew I did that. I am going to guess it would be pretty expensive with barleywine, not to mention the epic PITA racking through ice would be.
I have been thinking about trying out a few $3 or under wines, that do not have nitrates in them, splitting the bottle and freezing concentrating it. I have also thought about doing this with an imperial store bought beer. I will suggest this for others to try. so you can get a good understanding of what it will do to your beer before you attempt this. crying over a $3 bottle of wine or a store bought imperial is a much small tear than a screwed up batch of really good home brew barley wine, IMO.
GL and happy concentration!
