Prize::: Mail-order wife from Brazil :)

Riddle: There is a barrel with no lid and some wine in it. “This barrel of wine is more than half full,” said Curly. “No it’s not,” says Mo. “It’s less than half full.”

Without any measuring implements and without removing any wine from the barrel, how can they easily determine who is correct?

Prize::: Mail-order wife from Brazil 🙂

Answer is in comments!