Today in 2014, just one year ago, US Patent EP 2450290 B1 was issued, an invention of William P. Apps, assigned to Rehrig Pacific Company, for his “Plastic Beer Keg.” There’s no Abstract, but there’s a lengthy summary after the introduction which appears to serve the same function:

According to the present invention there is provided a plastic beer keg as claimed in claim I and a method as claimed in claim 6. The locking ring secures the liner to the lid, and the locking ring is configured to release the liner from the lid upon impact of the keg in a drop. This can be accomplished by molding the locking ring from a softer material, which flexes to release the liner on impact, or a more brittle locking ring or a locking ring with design-in stress concentrators, which breaks to release the liner on impact.

In the method of the present invention, the liner of the beer keg is filled with beer while the locking ring is securing the neck portion of the liner to the lid, but the locking ring is removed after filling and prior to shipping of the beer keg. The filled keg is shipped, sold and used without the locking ring. The locking ring may be reused in the filling of many kegs.

Also disclosed is a plastic keg that includes a liner including a neck portion and a body portion. A lid having an opening is disposed at least partially over the liner. The liner is disposed in an outer container having a wall with at least one locking rib projecting therefrom. The locking rib angles downward and the lid secured to the outer container by the at least one locking rib. Optionally, the lid can be snapped onto the locking rib or rotated to lock onto the locking rib. This can be accomplished by an angled surface on at least one of the locking rib and the shoulder of the lid that snaps under the locking rib.