Translation:In the evening we drink a bottle of wine.
It's simply another case of Italian being annoyingly idiomatic to non-native speakers.
When you use the definitive article with periods of time, like days, or parts of days, it's pointing to a routinised activity.
"Il sabato mangiamo pollo" - On Saturdays, we eat chicken.
"La sera mangiamo carne" - In the evening, we eat meat.
"La mattina beviamo latte" - In the morning, we drink milk.
I might be incorrect on this because I'm not a native speaker, but this is what I've gathered thus far.