Is half enough?

Check out this jar of grape jam:

 Nice jar of jam.

Notice the label,

it indicates that the jar contains 2lbs of jam.

Now check out the back label:

Hmn, every TWO POUND JAR

Starts out with ONE POUND of grapes.

What's the other pound made of?

(you only get one guess)

...and they're PROUD that the contents of the jar is only HALF GRAPES!