Leftover food: Reheat and live to tell the tale

The statistics are truly shocking: About 17% of the total amount of food produced in the world is wasted — that's more than 930 million tons of food according to a UN Environment Programme Food Waste Index report from 2021 — and 61% of that waste happens in our homes.

At the same time, 3.1 billion people on the planet cannot afford to buy or cook food for a healthy diet for themselves and their families.

Wasted food is also a matter of wasting global resources — water, land and electricity, for instance — used in the production of food.

Holidays are notorious for overindulgence and lots of leftovers. Much of those end up in the refrigerator, forgotten until spoiled by bacteria and mold, after which they land in the garbage.

But, with a few simple tips, you can enjoy your festive food while reducing waste — and without getting food poisoning in the process.

What is food waste?

Food waste happens at all stages of the food chain — "from farm to fork" — but most of it happens in households: Over 54% of food is wasted by you and me, 7% at wholesale and retail, and 9% in restaurants and food service.

All together, that's equivalent to 131 kilograms (288 pounds) per person, per year.

How can I reduce my food waste?

The UN Food and Agriculture Organization has a 15-point list of tips on how to avoid wasting food. Here are a few useful ideas:

Buy only what you need: Takes a bit of planning, but it's worth it.

Understand the difference between "best before" and "use by": If food has passed the use-by date, don't eat it — or, put another way, if you buy something that's close to its use-by date, make sure you can consume it while it's still safe. And if your milk has passed its best-before date, smell it to determine whether it's off.

Store leftovers: Use airtight containers to keep unwrapped foods fresh in the fridge and ensure that packets are closed to keep food fresher for longer and to stop insects from getting in.

Eat leftovers, but safely: Leftovers can be frozen or "remixed" in a dish for the next day. Just make sure that when you do this, to reheat leftover food so it is hot enough to kill bacteria. If you reheat a dish but still don't finish it, trash the rest. You should only reheat food once.

Food donations: Sharing is caring — donate food to friends or neighbors.

How can I store food safely?

Leftover food is a common cause of food poisoning. It's important to observe the so-called four Cs when storing and eating leftover food to avoid getting an upset stomach:

Cleaning: Keep your hands, work surfaces, utensils, chopping boards and kitchen cloths clean. It's common to "wash" raw meat under a running tap before cooking, but research shows that this actually increases the risk of cross-contamination around the kitchen. So wipe surfaces down and replace or wash cloths and tea towels regularly.

Chilling: Store food in appropriate containers. Glass is good for meats — it's easy to wash well and less likely to scratch than plastic, leaving crevices where food remnants and bacteria can get stuck and grow.

Cooking: There are many different things to observe when cooking, especially meats. Use a cooking thermometer to check meat is cooked through and use your eyes — if it looks raw, then it probably is (and therefore inedible). If you're cooking poultry, if there's any blood near the bone, it needs more time to cook.

Cross-contamination: Keep different types of foods — meat, fish, dairy, vegetables — separate to avoid bacterial growth spreading. And clean out your fridge regularly too for the same reason.

How can I safely reuse leftover food?

Cooking leftovers is the best way to kill any fungi or bacteria that could cause foodborne illnesses.

The US Department of Health and Human Services has a useful chart that lists how long you can store food in a refrigerator and in a freezer. The time limits vary from product to product.

When it comes to cooked food, the general advice is that leftovers should be used within three to four days.

Refrigeration does not stop bacterial and fungal growth, it only slows it down. 

There are two kinds of organisms that cause food to go off: Pathogenic bacteria that cause food poisoning, and spoilage bacteria and other organisms that cause food to develop bad smells, tastes and textures.  

Foodborne, pathogenic bacteria include E.coli, listeria and salmonella.

Spoilage organisms include yeasts, molds, fungi and bacteria.

As with any foods, raw or cooked, first use your eyes and senses of smell and touch to check whether the food in your fridge is still safe to eat.

No matter whether it's the first time you're cooking a dish or you're reheating leftovers, always cook your food well. There's no need to burn it, just cook it until it's piping hot and you see steam rise from it for at least a few minutes.

Keep turning or stirring the food as it heats or reheats to make sure it is cooked evenly and all the way through.     

Then sit down and enjoy!

Edited by: Fred Schwaller