Romance languages often use definite article plus bare noun to refer to a type/category, and for defining features that the each member of the category shares.
In English, we would use this constuction for countable nouns ("the whale is a mammal" i.e. whales-as-a-class, not a specific whale), but non-countable nouns don't add the definite article for denoting categories.
Something I'm not seeing in the comments / questions here is that "La birra" can mean "THE beer" if there's a specific one in context, or "Beer" in general, as in "all beer." I ran into this in French (I think it was -- long time ago). Same thing.
What I'd like to know is this: would it mean the same thing to say it without the "La" first? Or would that be wrong?
I'm going to expand on points made with a hypothesis.
Coupd it be that when starting a sentence with a subject that is msc or fmn you have to use the article "la" or "il". So "la birra è una bevanda"
But when the msc or fmn noun follows a verb like mangio, you don't need to include the articles "la" and "il".
Io mangio formaggio Io mangio pollo
Having said that my hypothesis falls down on these two examples.
Lui non mangia il manzo - he doesn't eat beef
Lui mangia la cena - he eats the dinner.
We'de rarely say the dinner or the beef. So it's hard to understand why the duo is being inconsistent. My guess is it could be a quirk of the language?