Many of us have full fridges and freezers right now, part of how we’ve prepared for the COVID-19 pandemic and shutdown.

But then the power goes out. Recent power outages caused by storms have brought plenty of safety questions when it comes to food and how long it can be kept.

Here is what you need to know.

How long is my food safe in an outage?

According to the U.S. Department of Agriculture, a fridge will keep food safely cool for about four hours if it is unopened during an outage.

So the first rule: Do not open your fridge or freezer.

A full freezer will hold the temperature for approximately 48 hours (24 hours if it is half full) if the door stays closed.

(Your fridge should be kept at or below 40 degrees Fahrenheit and your freezer should be at or below zero degrees).

And you should stick to the USDA guidelines very strictly, says Susan Adams, assistant professor of nutrition in the School of Nursing and Health Science at La Salle University.

She has one warning for people who want to see if their food is still good: “You can’t taste the food to see if it is OK,” she said. “You may not be able to taste and see a problem.”

If you can get the food to a cooler, do it. But it has to stay cooler than 40 degrees to be safe.

You can also cook what’s in your refrigerator right away. “This isn’t time to cook from a can on your shelf,” Adams said. “If the power comes back on quickly, you can freeze the prepared food. But if it doesn’t, you need to be prepared to throw it out.”

A basic rule: Food shouldn’t be out of the fridge for more than two hours. “Once the temperature goes above 40 degrees, you only have two hours before you have to throw the majority of your food out,” Adams said.

“You can’t have food in the danger zone — which is between 40 and 140 degrees Fahrenheit — after two hours.”

What food do I have to throw out?

Basically, the answer is most of it.

Maribel Alonso, the technical information specialist for the USDA, says that any open food in a refrigerator that has lost power for more than four hours should be thrown out.

“Also meat, poultry and seafood products, if they had soft cheeses or shredded cheeses, any dairy items such as milk, cream cheese, yogurt, they all have to get thrown away,” she said.

“Any open baby formula, egg products, and fruits and vegetables that have been cut have to go.”

What can I keep?

There are some things that will still be safe. Any fruits or vegetables that have not been cut and bread are a few examples.

Foodsafety.gov, an official website of the U.S. Government, lists the foods that should be discarded if the refrigerator or freezer outages are past the recommended time.

Things you can keep include: hard cheeses, like cheddar, Colby, Swiss, provolone, Parmesan, Romano (grated Parmesan or Romano are also fine), and processed cheese; butter and margarine; open fruit juice; peanut butter; and some dressings and condiments (ditch the fish sauce, mayo and creamy dressings, as well as pasta sauce).

How can I tell if food in my freezer has gone bad?

“You may have had some thawing a little bit, and when it refreezes it is going to be crystalized, so you are going to see crystals maybe on the outside of the package,” Adams says.

Alonso adds: If there is a big layer of frozen juice at the bottom of a package, that means the item completely thawed and refroze,” she said. “That has to get thrown out.”

Nobody likes to throw out food, “it breaks your heart throwing out food, but it would be horrific to have foodborne illness,” Adams says.

Can dry ice help?

“Yes,” said Alonso. “You can get a block of dry ice and keep the refrigerator and freezer as cold as possible.”

Alonso says that if a major storm is forecast, it might be prudent to get dry ice and be prepared for it.

Of course most people don’t need it until after there is an outage, and then it is difficult to acquire.

“Dry ice could help, but the problem is that during a power outage, it is hard to come by,” said John Williams of Continental Carbonic Products Inc., the Folcroft company that provides the product in eastern Pennsylvania, central and southern New Jersey, and Delaware. Williams said he ran out on Thursday.

Call around: Walmart and other major retailers may have some in stock.

Can I bring my food to a friend’s who has power?

Yes, but both Alonso and Adams say that a person has a two-hour window to transport food.

“Even if you go to the grocery store, you should not go food shopping and then do other errands and leave food out like that," Adams said. "There is a two-hour window.”