Asian family carrying cooler to picnic.

How to Keep the Food in Your Cooler Safe to Eat

June 21, 2024

Few things beat the heat like a picnic at the beach or barbeque at a local park. But are the burgers that have been sitting in the cooler for hours still safe to eat? And is the leftover potato salad okay to take home?

We asked microbiologist Daniel Green, MD, associate professor of pathology and cell biology at Columbia, to talk about the bacteria found in coolers and share tips for reducing the risk of foodborne illnesses.  

What kind of bacteria can grow in a cooler full of food?

Any kind can grow, especially when the temperature gets warmer.

When we're talking about food, we're talking about pathogenic bacteria (which cause foodborne illness) and spoilage bacteria (which cause food to deteriorate and develop bad smells, tastes, and textures).

How and why do these bacteria grow?

Like all organisms, bacteria want to grow and reproduce. This growth can accelerate if food is left at the wrong temperature for too long—especially within certain temperature ranges.

Pathogenic bacteria grow rapidly when food is between 40 and 140 °F, which is called the "danger zone." This type of bacteria is tricky because they usually don't change the taste, smell, or look of food. A certain number of pathogenic bacteria is required to cause infection, so when food is left at higher temperatures, the quantity of bacteria increases, making it more likely to cross the threshold amount that could make you sick.

Spoilage bacteria also grow faster above 40 °F, like in a refrigerator or cooler. This type of bacteria is easier to spot because it changes how food tastes, smells, and looks.

Why are bacteria bad for health?

First, not all bacteria are bad for your health. There are bacteria living in our stomachs and intestines that help us digest food and protect us from disease.

But there are some bacteria, like Salmonella, that enter the body, reproduce, and release toxins, causing sickness after hours or days.

Other types of bacteria enter your body with pre-formed toxins that grew at room temperature, causing immediate sickness, like vomiting.

What should everyone know about coolers and their health?

The ideal cooler is simply one that keeps food chilled for the longest amount of time. You don't need a fancy, expensive cooler, but you do need one that closes tightly.

The biggest risk when using a cooler is raw meat. Don't let it get warm, and don't let it leak into other things.

How to Pack Your Cooler

For more information on the best ways to store food in a cooler, the FDA and New York State Department of Health have detailed food safety guidelines. If you only remember one thing, it's this:

Bacteria thrive in that "danger zone" of 40°F to 140°F. As long as the temperature inside the cooler stays under 40 °F and the food itself has not expired, food packed in a cooler with ice is safe to eat.

If the temperature inside the cooler goes over 40 °F, the food is only safe to eat for two hours. Then, it must be discarded. If you can't tell what the temperature is in the cooler, and the food feels warm, discard perishable items, including meats and mayonnaise-based salads.

In addition, these easy packing tips will lower your chances of breeding bacteria at the beach:

  • Keep your cooler cool: Make sure your cooler is always in the coldest place available, like a basement before you fill it, or in a shady spot after it's full.
  • Use something colder than your freezer ice: When possible, use frozen ice packs or buy ice from supermarkets or a local bodega. Ice from your home refrigerator is not as cold as commercial ice. 
  • Line the bottom of the cooler with ice or ice packs: You could also fill empty milk cartons with water to make blocks of ice beforehand.
  • Be careful with raw meat: Because raw meat is the biggest cooler risk, pack all raw meat in a different cooler. If you only have one cooler, pack raw meat on the bottom to minimize the chance of any leaks seeping into other foods. 
  • Put food in air-tight bags or sealable containers: This reduces the chance of cross-contamination.
  • Separate food and drink: Pack drinks on one side of the cooler and food on the other, so you can quickly find what you want without leaving the cooler open. Or pack drinks and food in two different coolers; food usually stays colder for longer this way because people reach for drinks more.
  • Freeze some drinks to use as "ice:" They can thaw during the day.
  • Use as much ice as you can: Ideally, pack twice as much ice or ice packs as food and drinks. Fill empty spaces between foods with ice. A full cooler stays cold longer than a cooler that has empty space.
  • Observe the two-hour mark: Do not re-pack food that has been out of the cooler for more than two hours in warm weather; it is not safe to eat and should be discarded.
  • Wash up: After using your cooler, wash it with warm, soapy water. Spray with a water-vinegar solution, which helps to kill bacteria and prevent future growth. Air dry with the lid open.


Daniel Green, MD, is an associate professor of pathology and cell biology, and co-director of clinical microbiology at Columbia.