On Nutrition by Ed Blonz

Shelf Life of Milk Depends on Many Factors

DEAR DR. BLONZ: Dear Dr. Blonz, How long is milk good for once opened? My mother and I disagree, and I am counting on you to settle the debate. Irrespective of when it is opened, my mom looks at the sell-by date on the carton and insists that the milk will be good for at least a week past that date if refrigerated. I disagree, saying that once the milk container is opened, that date is no longer something to really look at. New milk cartons have about two weeks, that I've noticed, to sell. I cannot imagine that milk is good for at least three weeks if opened right away. My mom gave my kids milk on April 6 that had a date of March 23 on it. She said it smelled fine, but my kids said it tasted funny. I was mad at her for even giving them such old milk. Please, who is correct? -- S.T., San Jose, CA.

DEAR S.T.: Fluid milk is a perishable food, and it will spoil. The sell-by date on the container is the last day on which the carton should be sold. Manufacturers use these dates to signal retailers how long to sell the product, and the dates include an allowance for normal home use. That means that a gallon container will typically have an earlier sell-by date than a quart container that comes from the same batch of milk.

Assuming it has been opened before the sell-by date stamped on the container, homogenized milk should keep for about 5-7 days once opened. Tell your mother that the clock begins when you open the carton. But there is some flex here. The fresher the milk, and the more time it spends at a chilled temperature, the longer it will remain wholesome. All things being equal, a carton with 10 days before its sell-by date will last longer than one opened on that date. Three weeks? That’s pressing it.

Also, keep in mind that the sell-by date is not a guarantee of freshness or safety. The breakdown of food is a gradual process and does not take place on one particular day. You always need to keep containers chilled and tightly closed. Never return unused milk to the container. Then there is the fact that the accuracy of any dating system relies on the proper handling of foods. If there's been mishandling by the manufacturer, trucker, supermarket or consumer, the life -- and safety -- of the product is subject to compromise. In the end, consumers must trust their eyes, nose and palate in addition to those numbers stamped on a carton. If you notice, as your kids did, an off taste, smell or appearance in any food product, forget the date and toss it out.

Send questions to: “On Nutrition,” Ed Blonz, c/o Andrews McMeel Syndication, 1130 Walnut St., Kansas City, MO, 64106. Send email inquiries to questions@blonz.com. Due to the volume of mail, personal replies cannot be provided.