Why don't packaged foods tell us when the contents will expire after the container is opened?

Consumers often wonder why the answers to this question are not on the jars, bags, and boxes of foods they purchase.  One of the experts who serves on the Shelf Life Advice Advisory Board--food scientist Dr. Catherine Cutter-- has provided us with the following detailed explanation:



"The expiration date of foods, once they are opened depends on a number of factors. These include, but are not limited to, the following: the temperature of storage (in the refrigerator or on the door), how much oxygen is found in the product (which will depend upon how much of the product is used and the amount of available air in the head space--which may lead to oxidation/rancidity), cross contamination from other foods and/or utensils, etc. 


"I've also read about the impact of reduced fat/sugar/salt on characteristics/properties of foods., High fat/sugar/fat foods tend to have lower water activities than foods formulated with less fat/sugar/salt. These differences in water activity may impact the shelf life of some foods.


"For example, full sugar jam may last longer in the fridge than jams made with artificial sweeteners. Higher amounts of sugar help to bind up the available water in the jam. For low sugar jams, you have to add more pectin or other jelling compounds to help bind up the water. The addition of preservatives also can help when there aren’t enough other compounds to bind the water."


As you can see, the possibilities affecting the open shelf life of edible products are too numerous to get on the packaging! Also, some (such as the temperature of the individual consumer's fridge and the amount of food left in the opened container) relate to what happens to products in individual homes once they are partially used.  These effects are impossible for the manufacturer to calculate.  


All that having been said, I must point out that some organic soups give consumers the following message: "After opening, keep refrigerated and use within 7-10 days."  Wouldn't it be nice if similar guidance appeared on more food packages?



Catherine Nettles Cutter, Ph.D., Pennsylvania State University, Department of Food Science



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