DEAR DR. BLONZ: How long should milk be kept after the carton has been opened? -- S.T., Ripon, Wis.
DEAR S.T.: Milk and other dairy products usually have a sell-by date stamped on the container. Fluid milk is a perishable and it will spoil. The date on the container is the last day on which the carton should be sold. Manufacturers use these dates to tell 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 prior to the sell-by date stamped on the container, a conservative estimate is that homogenized milk should keep for about five days. The point is that the clock begins ticking as soon as the carton is opened. 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. Of course, a carton opened 10 days before its sell-by date will last longer than one opened on the sell-by date.
Please understand 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 back to the container. The accuracy of any dating system relies on the proper handling of foods. If there's been any mishandling by the manufacturer, trucker, supermarket or consumer, the life and safety of the product will be compromised.
In the end, consumers must trust their eyes, nose and palate in addition to the numbers stamped on a carton. If you notice an "off" taste, smell or appearance in any food, forget the date and toss it out.
DEAR DR. BLONZ: You will probably get a number of emails on this matter, but a plantain is a fruit, even if it is eaten as a vegetable. Even though seedless, it develops in the reproductive system of the plant. A vegetable is any other part of the plant, i.e., root, stem, flower. -- J.R.
DEAR J.R.: My apologies for the gaffe; thanks for pointing it out.
DEAR DR. BLONZ: I recently purchased a jar of peanut butter that was clearly marked "NO TRANS FAT per serving" However, in the "Ingredients" column, it listed partially hydrogenated vegetable oils (cottonseed, soybean and rapeseed). Is it possible that a food could contain partially hydrogenated vegetable oils but not trans fats? -- G.G., San Jose, Calif.
DEAR G.D.: Only a fraction of the fats undergoing partial hydrogenation will become trans fats; that percentage is determined by the starting material and the degree of hydrogenation desired. If there is no more than 0.5 grams of trans fat per serving, a product can be labeled as being "free" of trans fats.
I know that the advice is to zero out our trans fat intake, and this is something I support, but at the level of less than one half of one gram per day, there is no evidence that trans fats would have a measurable negative impact on health. It could become an issue if multiple servings were routinely consumed.
Send questions to: "On Nutrition," Ed Blonz, c/o Universal Uclick, 1130 Walnut St., Kansas City, MO, 64106. Send email inquiries to email@example.com. Due to the volume of mail, personal replies cannot be provided.