on draft
Drawn or served from a large container, especially a keg, as opposed to individual bottles or containers. (Spelled "on draught" in British English.) We have a wide range of craft beers on draft, including some from our own in-house microbrewery.
on ˈdraught
(British English) (of beer) taken from a barrel (= a large container): This beer is not available on draught (= it is available only in bottles or cans).