At around 11:00 in this episode of Tales from the Green Valley they are making March beer and they make sure to differentiate ale from beer. They say that ale would spoil while beer would keep. Now I always knew of ale as a style of beer so did the words have different meanings in the Stuart period or was it a slip of the tongue by the show's experts?
From the Oxord English Dictionary:
With the introduction of regular use of hops into England from at least the 15th cent., ale came to designate beer brewed without hops, a distinction which lasted until the 18th cent., when it came to refer to a strong beer.
Hops kills certain bacteria in beer, allowing the brewing agent to have less "competition." Thus, a drink without hops wouldn't keep as long.