If I go to a local microbrewery and ask them if the beers they have currently on tap are vegan and completely shellfish free, is that enough to allow me to consume the beer?
Do I need to be concerned about previous runs that may have had shellfish and treifed up their vats or kelim? Or is my only concern this specific beer that I want to drink?
The vats/kettles are normally cleaned very well between different variations of beer. Nothing to worry about with the Keilim.
Regarding oysters etc, my understanding is that is has to be declared based on TTB regulation. However I don’t know what goes on in the small places.
I would suggest being upfront and asking them what ingredients/ flavorings are used in the particular beer you’re looking to buy. If all ingredients are Kosher, you’re good to go.