19th century painters may have primed their canvases with beer-brewing leftovers
sciencenews.org
sciencenews.org
They also brewed a LOT in the 18c there. I think it'd be more plausible that air-residue landed on the paintings while they were being made.
It's also an art authenticity check too. Destructive, sure, but can be done carefully.
But, yes, the Danes did brew a lot, into the 20th century, since beer was the daily drink for Danish farmers.
quite artistic