But it's even harder to entice Americans to drink milk out of a box. In focus groups, U.S. consumers say they have trouble believing the milk is not spoiled or unsafe. In addition, they consider the square, quart-sized boxes more suitable for dry food. Many school and fast-food chains already buy UHT milk because of its long shelf life. Still, although Americans may not think twice about drinking a Mc Flurry from McDonald's made with shelf-stable milk, it's going to be a long, uphill battle to change their perceptions about the proper partner for a bagful of Oreos.