The Spain international striker has enjoyed a resurgence in form this season and, alongside Arsenal's Alexis Sanchez, leads the goalscoring charts in the Premier League with 12 from his first 15 games.
A picture emerged showing Costa's man-of-the-match award from last Sunday's 1-0 win over West Brom alongside a bottle of beer in the Chelsea dressing-room, prompting conflicting reactions from fans on social media.
Conte has imposed strict rules on his players when it comes to their diet but he is happy to allow them a drink immediately after games as long as they limit themselves to one.
"It's good for rehydration, you can drink Coca-Cola or one beer," he told a media conference. "It's good for recovery. But one. Not a lot. After you finish the game, quickly, not an hour after the end.
"I have great professionals in my players. In this case, I don't think a coach or a manager can say 'do this' or 'don't do this'. I have great professionals and I know they will have a better attitude and behaviour in this situation."
Chelsea face bottom-club Sunderland at the Stadium of Light on Wednesday.