The temperature in my freezer is set at zero degrees Fahrenheit. Is that setting too low? Should I bump it up a few degrees? After all, water freezes at 32. Wouldn’t 15 degrees be a good setting? Or 20?

Absolutely not. Zero degrees is the ideal temperature for frozen food. To understand why, let’s consider how food spoils. The major factors are microorganisms, enzymes, air, light, and temperature.

Microorganisms, including bacteria, mold, and yeast, can be grouped into three categories: beneficial, spoilage, and pathogenic. Beneficial microbes, such as those in certain yogurts, do our guts good when we ingest them. Spoilage microbes don’t harm us, but make food taste bad. Pathogenic microbes can make us ill or kill us.

Enzymes, which are naturally present in foods, are responsible for the ripening process in fruits and vegetables. They cause not just ripening, but over-ripening as well.

When air reacts with components in food, a chemical process called oxidation can produce changes in color, flavor, and nutritional content.

Exposure to light makes some foods change color and can also cause the loss of vitamin content.

When food it stored in airtight containers in a dark freezer at zero degrees, all of the above factors are slowed to a near standstill. At temperatures between zero and 32, the processes are slowed, but not stopped. Yes, water freezes at 32 degrees, but a lot of bacteria and enzymes don’t care. They carry on growing and spoiling. Same for 20 or 15 or even five degrees. At zero, though, they are forced to go dormant.

If zero degrees is good, wouldn’t -10 or -22 be better? Not really. What zero degrees does to bacteria and enzymes isn’t intensified at lower temps. Setting your freezer lower than zero uses more energy, but doesn’t provide extra benefit.

Bacteria grow best between 40 and 140 degrees. At 40 and below, bacterial growth is slowed enough that food will keep for a week or so in the fridge. Above 140, bacteria suffer from the heat. In between, they are free to go crazy. So the ideal temperature settings are zero for freezers and a few degrees below 40 for fridges.

If there is a power outage and your frozen stuff thaws but stays below 40 degrees, it’s usually okay to refreeze it back to zero when the power comes on.

The idea that you can’t refreeze food is, in part, a myth. If it is thawed properly in the fridge, stays below 40 degrees, doesn’t sit in there for days, and isn’t spoiled, it can be safely refrozen. Even meat and fish. (I leave this decision, however, entirely up to you.)

Food should not be thawed in water (running or not), in a microwave, or at room temperature. You’re begging for dysentery. Or worse. And food thawed in these ways should not be refrozen.

Here’s a poetic recap. Say it with me: “Freezer at zero, you’re a hero. Fridge at 38, food keeps great. Wrongful thawing, ambulance calling.”

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