Food Freshness

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Sometimes we do experiments in our kitchen, even when we don’t mean to.  Like when the ends of the bread get pushed to the back of a shelf behind some other stuff and mold starts to grow.  It’s gross, but it’s science! Nobody wants to eat moldy bread!  It’s pretty easy to see that we shouldn’t eat moldy bread, but what about other foods?  Is it bad to eat food that too old?  How do we know what old means?

To help with the last question, many foods come labeled dates.  The dates can be confusing—what is the difference between “sell by”, “use by”, and “best if used by”?  This just raises more questions—what do all these different phrases mean? 

You might think that the various dates stamped on food are provided to help keep people healthy.  Bacteria are everywhere, it’s not really possible to produce many foods with no bacteria, and, over time, the number of some kinds of bacteria could grow large enough to cause people to get sick—sometimes really sick.   But, food dating is not about safety—dangerous bacteria grow in food that is not stored/cooked properly.  So, be sure to follow safety guidelines for storing, defrosting and cooking food thoroughly to help prevent foodborne illness (food poisoning).  And never open a bulging can!

So, if dates are not about food safety, why print them on food packages?  The USDA (United States Department of Agriculture) provides information about food dating.  According to the USDA, infant formula is the only food that must have a “use by” date on the label.  All the other dates are provided by the manufacturer to help people decide when the food is the best quality.  Even if a food is out of date, it is probably not spoiled; it just may be beyond the peak of flavor.   

OK—so when we look at sell by dates we should be thinking about food quality.  When is it best to eat?  When should it be thrown out?   The good news is that it’s usually easy to detect when food is spoiled.  When milk is spoiled it tastes bad.  Bread gets moldy.  So, even if it’s past the “sell by” date, the food is probably still ok to eat—it might not be at its absolute best, but the difference in quality is likely to be quite small.  You might not want to pay money for “old” food, especially if you plan to store it at home, but eating food past the “sell by” date has probably not caused disease.

We should use common sense in deciding what to eat.  Things that smell, look or taste bad, should not be eaten.  But, if the box of cereal is dated last month, it’s most likely fine to eat.  At worst, it might be a bit soggy!   


1.  How do we tell when food is spoiled?

2.  Is it true that Twinkies never spoil?

3.  What about McDonald’s hamburgers? 

4.  Is it true that stores can sell things past the date stamped on the package?

5.  What about dairy products—don’t dates matter for them?

6. Can we investigate food spoiling at home?