noun
keg
KEG/keɡ/
A small barrel for holding liquids.
The small keg rests in its cradle with a tap ready for use.

Etymology
The word comes from a Scandinavian source such as Old Norse kaggi, “cask,” whose deeper origin is unknown. The specific beer-container sense narrows that older general meaning to a small or half barrel.
In context
the argument being the quicker you got the keg back to the brewery you could fill it up again and get it out again