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Sanitation, ultra-pasteurization makes milk last Jan 31, 2017 12:00 AM A A This old guy is still a big milk drinker. When I was younger, I remember having to drink milk within three or four days or else it'd sour. I'd like to know how milk's gone from that to expiration dates of a couple weeks or more. Are the cows doing something different? — 'Old Guy' We'd like to imagine cows are just trying harder these days, Old Guy, but that would discount a lot of changes in the dairy industry. Roseburg-based Umpqua Dairy says that its milk can remain fresh five days past the sell-by date, much longer than 3 or 4 days, in part because its milk is processed quickly in a modern facility with automated procedures that ensure equipment is regularly cleaned and sanitized, according to the company's website. If you've ever bought Darigold milk in cartons, you've probably noticed sell-by dates more than a month away. That's thanks to the magic of ultra-pasteurization, which nearly quadruples its shelf life without affecting nutrition or taste. Standard pasteurized milk has an 18-day shelf life because it'd been heated to 167 degrees for 15 seconds. Ultra-pasteurized milk, however, is heated to 280 degrees Fahrenheit for two seconds, giving it a 60-day shelf life. Much of that packaging technology was developed by Swiss company Tetra Pak, whose logo you may notice on cartons. The company innovated many of the "asceptic processing" systems using cardboard packaging in the 1950s and 1960s. — Send questions to “Since You Asked,” Mail Tribune Newsroom, P.O. Box 1108, Medford, OR 97501; by fax to 541-776-4376; or by email to [email protected]. To see a collection of columns, go to mailtribune.com/youasked. We’re sorry, but the volume of questions received prevents us from answering all of them.