All Grade A milk sold in stores is pasteurized, or heated to kill most of the microorganisms that can make it spoil quickly. But many organic milk companies employ a process known as ultrapasteurization (indicated on package) in which milk is heated at a higher temperature until it is practically free of organisms that can grow at refrigeration temperatures; this allows it to last one to two months instead of the 10 to 12 days you may be accustomed to. However, it is important to note that the sell-by date on ultra-pasteurized products is only relevant before you open the carton. After that, the milk stays fresh for a week or so.
Ultrapasteurization isn't used only for organic milk, but it is particularly advantageous for this product. An extended expiration date enables organic dairies to ship their products farther and allows stores to receive shipments less often. "Organic milk isn't produced in all parts of the country, so ultrapasteurization is a way for companies to reach more customers," says Sharon Gerdes, technical consultant for Dairy Management, which represents U.S. dairy farmers.
Milk that has been ultra-pasteurized has a subtly different taste and texture (some people notice a slight "cooked" flavor) than regular varieties. It is also pricier, because ultrapasteurization requires dairies to invest in more sophisticated equipment. If supporting local dairies is a priority, keep in mind that while pasteurized milk is often bottled locally, ultra-pasteurized products may have traveled a significant distance to reach your store.