1015 Sweet Onions If you’ve never tasted a fresh, sweet onion, you’re in for a treat. Because they’re so sweet and mild, yet still deliver great onion flavor, they’re something you’ll want to keep on hand all the time. A sweet onion should contain at least 6% sugar to be in the sweet category. Another big plus is they are a virtually tear free onion, and they deliver a burst of sweetness when bitten into.