Storing and Reheating Leftovers: Sorting the Evidence From the Noise

Key takeaways

• Refrigerate within: 2 hours of cooking, or 1 hour if the room or outdoors is above 90°F (32°C)
• Use refrigerated leftovers within: 3 to 4 days
• Most useful single change: Divide large amounts into shallow containers so they cool quickly in the refrigerator.
• Commonest mistake: Leaving food out to cool on the counter for hours before refrigerating it.
• See a doctor if any of the signs under "When to speak to a doctor" below apply to you.

What it is

How to cool, store and reheat cooked food so bacteria do not have time to multiply. It sits within Food Safety. What follows are the published numbers, not the ones that get passed around.

The numbers, in one place

What helps

You do not have to do all of it, and you do not have to start today.

• Divide large amounts into shallow containers so they cool quickly in the refrigerator
• Label containers with the date you cooked the food
• Thaw frozen leftovers in the refrigerator or microwave and reheat them right away
• Cover food when microwaving and stir halfway through so it heats evenly

What to avoid

Things that seem reasonable and are not.

• Leaving food out to cool on the counter for hours before refrigerating it
• Smelling or tasting food to decide if it is safe; most germs that cause illness do not change taste or smell
• Keeping takeout or party food that sat out longer than 2 hours

In depth

Leftovers become risky not because they are old in themselves but because of what happens while they cool and sit. Bacteria that survive cooking, or that reach food afterward from hands and utensils, can multiply quickly in the danger zone between 40°F and 140°F (4°C to 60°C). The longer food stays in that range, the more bacteria there are, and some types produce toxins along the way. The goal of safe storage is to move food through that zone quickly and keep it out.

Certain germs are particularly associated with leftovers. Clostridium perfringens thrives in large pots of stews, chili, gravy and roasts that cool slowly, and it is one of the most common causes of foodborne illness in the US. Bacillus cereus is linked to cooked rice and pasta left at room temperature. Staphylococcus aureus can spread from hands to food. Toxins from Staphylococcus and some Bacillus cereus strains are not destroyed by reheating, which is why reheating cannot rescue food that was left out too long.

Refrigeration slows bacterial growth but does not stop it entirely, and a few germs such as Listeria can grow slowly even in the cold. That is the reasoning behind the 3 to 4 day limit for refrigerated leftovers. Freezing at 0°F (-18°C) stops growth altogether, so frozen food stays safe indefinitely, although its texture and flavor decline over time. Neither the refrigerator nor the freezer kills germs already present, so food must still be reheated thoroughly.

Signs and symptoms

• Nausea and vomiting starting within a few hours of eating, typical of toxins from Staphylococcus or Bacillus cereus
• Stomach cramps and diarrhea starting 6 to 24 hours later, typical of Clostridium perfringens
• Several people falling ill after a party or buffet
• Fever and diarrhea a day or more later from other bacteria
• Weakness or dizziness from fluid loss

Causes and risk factors

• Cooling large, deep pots of food slowly on the stove or counter
• Leaving buffets, takeout or party food out for hours
• Keeping leftovers longer than 3 to 4 days in the refrigerator
• Reheating food only until warm instead of to 165°F (74°C)
• Refrigerators set above 40°F (4°C) or overpacked so cold air cannot circulate
• Reheating leftovers in a slow cooker, which warms food too slowly

How it is checked

Illness from leftovers is usually short and diagnosed from the pattern of symptoms and timing. Toxin-related illness from Staphylococcus or Bacillus cereus typically causes sudden vomiting within hours and clears within a day or so. Your doctor may not test for these, since they usually resolve on their own.

Testing is more likely if symptoms are severe, include blood or a high fever, or last more than a few days. If several people became ill after the same event, tell your doctor, and consider contacting your local health department, which may investigate and may be able to test leftover food that was kept.

Treatment and support options

Cool food quickly

Divide large amounts of hot food into smaller portions in shallow containers so heat can escape. Cut roasts into smaller pieces and remove meat from the bone. It is fine to put hot food straight into the refrigerator; modern refrigerators can handle it, and waiting for food to cool on the counter keeps it in the danger zone longer. Leave space around containers so cold air can circulate.

Reheat thoroughly

Reheat leftovers to 165°F (74°C), checking the center with a food thermometer. In the microwave, cover the food, add a little liquid if needed, stir or rotate partway through and let it stand before checking, because microwaves leave cold spots. Bring soups, sauces and gravies to a rolling boil. Use the stovetop, oven or microwave rather than a slow cooker or chafing dish for reheating.

Freeze for longer storage

If you will not eat leftovers within 3 to 4 days, freeze them soon after cooking rather than at the end of that window. Use airtight containers or freezer bags with the air pressed out to reduce freezer burn. Thaw in the refrigerator, in cold water or in the microwave, and reheat right away. Food thawed in the refrigerator can be refrozen, although quality may suffer.

Plan portions

Cooking amounts closer to what you will eat, and portioning extras into single meals before serving, cuts down on food that sits out on the table or gets reheated repeatedly. Reheat only what you will eat at that meal, and if food is reheated and not finished, it is safest to throw it out rather than chill and reheat it again.

Prevention

• Set a timer or reminder to put food away within 2 hours of serving
• Keep an appliance thermometer in the refrigerator and freezer
• Use a marker or labels to date every container of leftovers
• Move food from opened cans into storage containers before refrigerating
• Clean out the refrigerator once a week and discard anything past 3 to 4 days

Day to day

Leftovers are a practical way to save money and time, and a few routines make them safe without much effort. Many families pick one evening a week, often the night before trash collection, to check the refrigerator and use or discard older food. Storing leftovers at eye level, in clear containers, makes them easier to see and less likely to be forgotten at the back of a shelf.

Takeout and restaurant food count as leftovers from the time they were cooked, not from the time you got home. If you are traveling home a long way, or the food sat in a hot car, it may already have used up much of its safe time. For packed lunches, use an insulated bag with a cold pack, and refrigerate the lunch when you arrive if a refrigerator is available.

For specific groups

Pregnancy

Because Listeria can grow in the refrigerator, pregnant people are advised to eat leftovers well within the 3 to 4 day window and reheat them until steaming hot. Ready-to-eat foods such as deli salads deserve particular care.

Older adults living alone

Cooking for one often means more leftovers and a fuller refrigerator. Labeling dates clearly, freezing single portions and checking that the refrigerator stays at 40°F (4°C) or below help, especially if sense of smell has weakened.

Families with young children

Do not save food a baby has eaten from directly, because saliva introduces bacteria. Serve baby food into a separate dish and refrigerate the unused portion from the jar promptly.

Questions to ask your doctor

• Could my symptoms be a toxin-related illness that will pass quickly?
• How do I know if I am getting dehydrated?
• When should I be tested rather than waiting it out?
• Is there anything I should avoid eating while I recover?
• Does my condition or medicine mean I should be stricter about leftovers?

More questions, answered

Is it safe to put hot food straight in the refrigerator?

Yes. USDA advises refrigerating food promptly rather than letting it cool on the counter. Splitting large amounts into shallow containers helps food cool quickly without warming up other items in the refrigerator.

Can I reheat leftovers more than once?

Food reheated to 165°F (74°C) is safe, but each round of cooling and reheating adds time in the danger zone and lowers quality. It is better to reheat only the portion you plan to eat and leave the rest in the refrigerator.

Why is reheated rice sometimes mentioned as a risk?

Cooked rice can carry spores of Bacillus cereus, which survive cooking. If rice sits at room temperature, the spores can grow and produce toxins that reheating does not destroy. Cool rice quickly, refrigerate it within 2 hours and use it within a few days.

Is pizza left out overnight safe to eat?

No. Pizza with cheese, meat or vegetables is perishable, and food left at room temperature for more than 2 hours should be thrown out. Reheating it does not reliably make it safe, because some bacterial toxins survive heat.

Does freezing kill bacteria?

No. Freezing at 0°F (-18°C) stops bacteria from growing, but most survive and become active again as food thaws. Thaw food safely and cook or reheat it thoroughly.

If leftovers smell fine, are they safe?

Not necessarily. Spoilage bacteria cause bad smells and slime, but most bacteria that make people ill do not change how food looks, smells or tastes. Go by how long food has been stored and how it was handled, not by smell.

Related topics

• What the Guidance Really Says About Meal Planning (Nutrition)
• Batch Cooking: Sorting the Evidence From the Noise (Healthy Recipes)
• Food and Water Safety Abroad: Sorting the Evidence From the Noise (Travel Health)
• Storing Medicines: What Published Guidance Supports (Medicines Safety)

Where to go next

• Storing and Reheating Leftovers: Common Questions Answered
• Storing and Reheating Leftovers: Just the Figures
• Storing and Reheating Leftovers — the reference entry
• Food Safety: The Complete Guide
• Food Recalls: Sorting the Evidence From the Noise
• Raw Milk: Sorting the Evidence From the Noise

When to speak to a doctor

See your doctor if vomiting or diarrhea lasts more than a few days, comes with a high fever or blood, or affects someone who is pregnant, very young, older or has a weakened immune system. Call 911 for severe dehydration, confusion or fainting.

Where this comes from

• USDA — Leftovers and Food Safety
• CDC — Four Steps to Food Safety

How this page was put together

Every figure, recommendation and warning above is taken from the guidance named in Where this comes from. Nothing on this page is inferred, summarized or generalized beyond what those bodies publish: where they give a number, it is their number, and where they are silent, so are we. Pages are rebuilt whenever the underlying record changes. Sign-off by a named clinician, where it has happened, is shown at the top of the page along with the date.

Medical disclaimer

This article is general information, not medical advice. It cannot account for your own history, medication or circumstances. Always speak to your doctor, pharmacist or another qualified health professional before making changes that affect your treatment, and never delay seeking medical advice because of something you have read here. In an emergency, call 911.