2Turns out, the major difference lies in the method by which milk is processed. Almost all milk is pasteurized, meaning it undergoes extreme heat in order to kill illness-causing bacteria. The U.S. and Canada use a pasteurizing technique called high-temperature short-time pasteurization, or HTST. HTST is cheaper and more efficient because it processes milk in larger batches, but as a result, milk has a shorter shelf life—around seven to ten days—and must be refrigerated.
