Between the time you pack a lunchbox in the morning, and the moment your kid opens it up in the cafeteria, several hours have passed. Perishable foods shouldn’t be in the “danger zone” for more than two hours, so it’s worth paying attention to time and temperature as you’re packing that meal.
The “danger zone” is 40 to 140°F. In other words, perishable foods are safe when they are in the fridge (under 40 degrees) or while they’re being cooked (a simmering soup will easily be over 140). But bacteria can grow, potentially making food unsafe to eat, after a few hours at middling temperatures. A lunchbox in a school coatroom would be the perfect example of that—depending on how you pack it.
Some foods will last longer than others in the danger zone; for example, cheese isn’t likely to kill you after a few hours out of the fridge, but it may not look or taste very good. If your kid is a picky eater, and their lunches tend to come back only half-eaten, this may be why.
Which foods need an ice pack
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Fortunately, there’s an easy way to keep cold foods cold: Use a soft-sided insulated lunchbox, as the USDA recommends, and include at least one cold pack. (The USDA actually recommends two—for example, a gel pack and a frozen water bottle.)
Insulated lunchboxes really are your best bet, and fortunately they are the most common type you’ll see for sale next to the school supplies. Old-fashioned metal lunchboxes, or even the classic brown paper bag, won’t keep a lunch cold very long. (You can still use them for shelf-stable foods, which we’ll mention below.)
Foods that should be kept cold, with an ice pack or a frozen water bottle, include:
- Deli meats (and sandwiches made with them)
- Fruit that has been cut up
- Dairy products like yogurt and milk
- Cooked vegetables
- Most cooked foods (like leftovers from dinner)
- Hard-boiled eggs
- Canned or other shelf-stable food that has been opened
You can even freeze some of these items. A frozen GoGurt can act as a cold pack, for example, and will usually be soft enough to eat by lunchtime.
What to pack if you can’t keep food cold
Even though a lot of foods need an ice pack to stay fresh, there are plenty that don’t. You can skip the ice pack for things on this list:
- Whole fruits, like an apple or orange
- Raw vegetables, like baby carrots or sliced peppers
- Crackers, cookies, bread, muffins, and other baked goods
- Peanut butter and jelly sandwiches (or similar sandwiches made with nut butters or seed butters)
- Tuna pouches or cans (sealed)
- Dried fruit, like raisins
- Nuts or trail mix
- Anything that is sold on unrefrigerated shelves and that is still sealed (like fruit cups or applesauce pouches)
- Juice boxes or ultra-high-temp pasteurized milk that is still sealed in its container
As a rule of thumb, if you keep it in a cabinet at home, it doesn’t need an ice pack. If you normally keep it in the fridge, it does.
How to safely pack hot foods
There is, of course, another way to keep foods out of the danger zone: Keep them hot. With a Thermos or an insulated food jar, you can keep soups or mac and cheese hot for hours.
While you’re getting the hot food ready, fill the empty insulated container with boiling water. Then pour out the water immediately before filling the container with piping hot food. (This is a hack that I thought I invented, but it turns out the USDA recommends it on their page about lunchbox food safety.)
If you’re not sure whether your food jar is keeping its contents hot enough, do a test run and check the internal temperature after the jar has been sitting around a while. If the food stays over 140° for a few hours, you’re good. You still have two hours after the temperature begins to drop before it’s considered unsafe to eat, so if the kid eats at noon, you want something that will stay over 140 until 10 or 11 a.m.