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Saving seconds: the science of food preservation

This article appeared in the November 25, 2012 edition of the Davis Enterprise.

By Lisa Justice
Special to the Enterprise

A typical Thanksgiving celebration involves preparing large amounts of food.  This results in lots of food left over days or even weeks later.

To keep that food fresh and safe to eat, many people wrap it in air tight packaging like a zipper lock plastic bag or plastic box with a snap on lid, and place it in the freezer.  Putting your leftover turkey in the freezer means you can take it out weeks later and it’s still good to eat.

Freezers help preserve some foods better than leaving food out on the table, or even putting it in the refrigerator.  The colder temperature of the freezer prevents more bacteria from growing on our food making it gross or dangerous to eat.

There are two types of bacteria that grow on food:  harmful bacteria that can give us food poisoning and make us sick, and spoilage bacteria that can make our food look and smell bad.  Refrigerators are cold enough to prevent most harmful bacteria for a few days, but don’t always prevent spoilage bacteria.

Freezers on the other hand are set to much lower temperatures (usually at or below 0ºF) and can better prevent both types of bacteria for longer periods of time.

You can experiment with how long certain foods survive in your refrigerator and freezer.  For this experiment you will need: a refrigerator and freezer, different types of leftover food, air tight storage containers, and a marker.

First, seal a small amount of food in each container.  Let’s test some turkey and some lettuce.  So put a bite of turkey in two containers and a leaf of lettuce in two more containers.

Label each container with the contents and today’s date.  We are going to use this food only for our science experiment; you don’t want to accidentally eat it later.

Place one container of each food in the refrigerator and the freezer.  Make sure your containers are air tight in case the food develops a bad smell.

Check on your food every day to observe any changes.  How long does the turkey in the refrigerator last before developing mold, a smell, or other signs of spoilage bacteria?  Does the turkey in the freezer last longer?  Why?

What about the lettuce?  What happens to the lettuce in the freezer?  Do you think you could thaw it and eat it like the turkey?

Lettuce has lots of water in it, and when the water freezes it expands.  This expansion breaks the lettuce’s cellular walls, so when you thaw the lettuce it has lost its crispy leaf structure.

After a day or two in the freezer, take the lettuce container out and warm it up to room temperature.  Observe the texture of your lettuce.  Is it different from when it was fresh?

Do you think the freezer will do the same thing to the turkey?  Why or why not?  In a week or so, thaw your turkey and see if you notice similar changes to the lettuce.


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