A beer stein is a traditionally German beer tankard or mug, made of earthenware or glass, and usually with a hinged lid and levered thumblift. Its capacity can range from one pint to many liters, with some Oktoberfest steins so large that they are too heavy to lift when full.
Lids, which technically distinguish a stein from a mug, started out as a sanitary measure. During the summers of the late 1400s, central Europe was repeatedly overwhelmed with swarms of flies. This soon led several principalities in what is now Germany to pass laws requiring food and beverage containers to be covered. By adding a hinged lid with a thumblift on the lid within reach of the mug handle, it was possible to keep a beverage covered and yet open it with the same hand by which it was held.
The word "stein" is a truncated form of Steinzeugkrug, which is German for stoneware jug or tankard. Stein in German means "rock", and is not used to describe the same object.
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