Pasteurizing grapefruit juice often leaves it tasting bitter. Food scientists at Cornell University, however, have developed an "active" container to battle this consumer turnoff. The bitterness in grapefruit juice is caused by culprits that include the acid naringin. By coating the inside of the carton with a cellulose-acetate film harboring an enzyme that breaks down the acid, the food scientists have made the juice taste sweeter. The Cornell group, led by Joseph Hotchkiss, says such cartons show the feasibility of "active packaging" that doesn't just passively protect its contents but actually improves the quality of the food it holds.