What is the difference between 'Beer' and 'Beers'? Which is correct? [duplicate]

Solution 1:

'Beer' can mean both the substance "beer" and the (standard or more arbitrary) units by which it is measured ("a beer"; "two beers").

'Beer' referring to the substance cannot be plural (or singular) (ie. it is non-countable, see comment).

But when used to mean the units by which you buy / consume the substance (eg. "we each had 3 beers last night"), 'beer' is countable. See this (Canadian) article at Ask the English Teacher and this comment in particular, for more clarity.

Solution 2:

The key issue here that the answers shown above missed is why the word "beer" treated specially (as both countable noun and uncountable noun). That is, the arguments (explanations) does not seem to hold if you replace the word "beer" with "milk".

Let me rephrase my point: Why is "beers" acceptable as proper English in certain cases whereas "milks" does not seem OK? In other words, it is not acceptable to say "Let's have milks", or is it?