According to Wine Country Getaways, there are 60 gallons in a barrel of wine. That calculates to about 300 standard-sized 750-milliliter bottles of wine in each barrel.
A standard case of wine is 12 bottles, so one wine barrel also yields about 25 cases of wine. An easy way to find out the quality of the wine a producer is making is to inquire about the tons yielded per acre of grapes grown in a given year. If the number is high for a year, then the wine quality is low. If the ton yield is low for a given year, the quality of the wine is high.