Mold can cause plenty of health problems. Some major. Some minor. It’s much like yeast, but far worse. With a few cheesy exceptions there’s no real benefit to mold. It produces toxins that make us sick. And if live spores set up camp in or on your body – you’ve got trouble. This article is specifically about how to stop mold, yeast and bacteria from growing on leftover foods. Mold itself is a big subject and covers a lot more than leftover roast beef.

There’s the mold that often arrives on basic ingredients you purchase at the store (which aren’t as basic as you may have thought). And then there’s mold in your environment (especially your kitchen, where it can end up floating onto your food). Mold is a big problem. And it can be more than one species. Molds produce toxins that make you ill. They can even live inside your body, consuming nutrients in your food and spitting out even more toxins. The symptoms range from fatigue, to headaches, to muscle pain, to fogginess, to outright food poisoning and death.

But let’s start with the mold found in most leftovers –you’d be surprised how much mold you may be eating in this form. And by leftovers I just don’t mean cooked leftovers. Raw leftovers can often be more of a problem as you’ll soon see.

Why Moldy Food is Such a Problem

Now along with mold growing on food, you can almost always guarantee its close cousin, yeast, will also be present. Along with mold and wild yeast expect a range of microscopic bacteria. Ingesting mold, bacteria and yeast is just part of life. A little bit even keeps your immune system strong and healthy by giving it something to defend against. But most people are getting far more than they should be and leftover foods are one of the most problematic areas.

The toxic residue and the threat of them taking up residence in your body are the main problems with mold and bacteria. The other lesser issue is that they suck nutrients out of your food. It’s one of the reasons leftovers have less nutritional value the next day – they’ve been partially consumed by mold.

What Exactly is Mold?

Mold, under a microscope, looks like skinny mushrooms. Its thread-like roots grow deep into the food it is living on. At the end of each stalk, spores form that allow the mold to spread through air and water.

What Mold, Yeast and Bacteria Need to Thrive

The good news is that – like most life forms on planet Earth – mold, yeast and bacteria need a certain set of conditions in order to thrive…and you can learn to manipulate these conditions.

  • Moisture: They “drink” water. Not much. Leftover al dente pasta will do fine. This is why dry foods (like dried fruits, jerky, grains, etc.) don’t spoil as easily. No moisture, less problems.
  • Nutrients: Mold, yeast and bacteria need nutrients. Which is why a lot of heavily processed foods don’t spoil easily either. Put out some processed snacks and the ants won’t even touch them.
  • pH Balance: They need a good pH balance. They like, more or less, what we like in the way of an alkaline-rich diet. So, they are your competition (living in your environment).
  • Room Temperature: They like room temperature. More or less what we like. 21oC or 70oF. That’s why cooking at high temperatures will kill them, cold refrigerators will retard them, and freezers will make them inert.
  • Oxygen: They need oxygen. Hence, air-tight containers and vacuum sealing is so popular. If they can’t breathe, they can’t eat, drink and be merry. And they can’t hold their breath!

More or less, they need what we need. So that’s part of the reason we are at war with mold. And like human beings, after they eat, mold and bacteria defecate (more or less). And like human defecation it’s not very healthy to eat. In fact, it’s even more toxic.

Now, obviously, mold can only survive on the outside of food – where there is oxygen. But don’t let that fool you. Their fine roots can reach one inch into your food. So, yes, if you think skimming off the green fuzz on the top of the week old spaghetti sauce is sufficient – make sure you skim at least one inch deep (though, you should probably just toss out the whole batch!).

How Does the Mold Get on the Food?

Good question. Quite easily, really. There’s mold everywhere. Spores fly through the air. They are in our water. They are on our hands. Of course, cooking food or washing food will kill or clean away the mold, yeast and bacteria.

But more is always on its way.

For now, suffice to say, that if you’re trying to avoid mold, you need to wash everything really well. Not just produce, but also  grains, meat, nuts and seeds. You can rinse all these foods with 5-10 drops of grapefruit seed extract in a bowl or sink full of water.

The Problem with Leftovers

Once you’ve prepared a dish (whether you cooked it or not) it’s going to start growing mold, feeding bacteria and fermenting yeast. If it was cooked, it’ll have to wait until it’s cooled down to below 43oC, or 109 oF, before this all begins. That’s why buffets keep their food heated and why in medieval times stew would stay simmering over the fire for a day or two.

On that note, you should make a point of keeping your food warm while you are waiting to serve it. If you make soup, keep it on a low heat. Even better is to keep it in a crock pot or in the oven where it will have heat surrounding it. You don’t just want only the bottom to be kept hot enough to render microbes inactive. A higher temperature and stirring will help make the whole dish safe. But the big issue with leftovers is when they hit the fridge. The cool temperature is not ideal for mold. But they still flourish. Just more slowly. You only need to leave something way in the back for long enough to see some blue-green proof of that.

And this is true just as much for raw food as cooked food. Of course, raw whole food is fine. As long as it has a skin that isn’t punctured. Fruit should do fine in or out of the fridge (for a reasonable amount of time). Why? Because no oxygen is getting to the fruit. Its skin protects it. That’s why as soon as you bruise or cut the skin the fruit begins to spoil. Especially moist fruit. The same is true for vegetables, more or less. They also have a lower moisture content which helps. Still, you need to make sure you clean them very well.

The problem, however, with raw dishes is that they make lousy leftovers. They are usually very difficult to clean after they are prepared. You make a fruit salad or raw apple crisp and store it in the fridge. Mold, bacteria and yeast grow while you are off doing other things. When you get to it again, there’s no way to clean it up. And since you can’t cook a salad (which will kill the invaders) you don’t have many options.

The Best Advice

Now, admittedly, the best advice– purely from a healthy eating standpoint – is to  not eat leftovers. Especially raw leftovers. At least with cooked leftovers you can reheat the dish and kill off any mold, yeast and bacteria. You can’t do this with most raw dishes.

So, as far as raw goes, I’d recommend you just prepare what you need and no more. Of course, you can take some anti-fungal herbal remedies like grapefruit seed extract when you eat raw leftovers and see how that works. Or, you can make raw dishes with antifungal ingredients like garlic, turmeric and onions. This will help. Or, you can check to see if that particular raw food will freeze well. Don’t bother with salad! Whether any of these options are enough will depend on the individual.

With cooked food you have a little less of an issue, as long as you REHEAT the leftovers. You need to essentially cook them again. This will kill the bacteria, mold and yeast. It will not, however, get rid of any toxins they left behind. Nor will it replenish any nutrients they suck out of the food. Nor will it “get rid of them.” You’ll still be ingesting them. And, suffice to say, reheating your food will further remove nutrients. As well, nutrients will be lost by the oxidation process of letting food sit for a time in your fridge.

So, the best advice I can give you is to limit or completely avoid eating leftover foods. This may not be as convenient but it certainly is healthier (and tastier!). Who really likes leftovers anyways? You’re better off either…

  1. Learning to love cooking (treat it like an artful service to your family).
  2. Learn to cook simply.
  3. Hire a chef or invest in a meal delivery service

You may find avoiding leftovers gives your health, your digestion, your skin tone, your sinuses, your sex life, your mental capacity a major boost. Many people find the health and wellbeing they gain from eating fresh food well worth the time it takes  to prepare. But you won’t know until you try it!

Leftovers are a Modern Invention

Yes, keep in mind… leftovers are a modern invention. Before refrigerators came along, man simply was not able to store prepared food without it spoiling. In northern climates, people such as the Inuit could easily freeze food in the winter. Otherwise the only storage method was drying. And,  even then, this was usually reserved for whole foods.

Would you eat day-old pasta that was not stored in the fridge? How about meat? Even if you do build up a strong immune system that can handle fuzzy ham – why do you want to waste your energy digesting rotting food?

Freezing Leftovers

If you are going to use leftovers there is one way that will eliminate much of the problem: Freeze them! Bacteria, mold and yeast cannot live in your freezer. It’s too cold. So instead of putting leftovers in the fridge, make sure they are stored in airtight containers and put in the freezer.

Of course, this isn’t as easy as just using your fridge. Frozen food takes time to thaw. But don’t thaw it in the fridge. And especially not on the counter. This will only create an environment for bacteria to grow on while it’s thawing. Particularly since the outside will thaw first. It’s best to just put take a freezer and oven-safe dish from the freezer and put it directly into the oven and reheat. If you’re reheating something like soup, then just put the container in hot water to thaw quickly enough to loosen it up and put it directly in a pot on the stove.

Ideally you want to freeze leftovers in glass jars or in actual baking dishes (so you don’t need to bother transferring, which is tricky). You can probably find little baking dishes that you can wrap well in plastic wrap. This way you can remove the plastic and just place the whole frozen entrée directly into an oven or toaster oven. The big advantage to the freezer is that you can come back to leftovers weeks or even months down the road. Generally, anytime within the next year is fine. Just make sure they are airtight.

Storing Leftovers in the Fridge

If you do store your leftovers in the fridge, make sure your fridge is set to just above freezing. You don’t want your food freezing rock solid, but you don’t want it getting too warm. Around 3oC to 4 oC is ideal. Check the temperature gauge and ensure it’s set properly.

Also, make sure you cover anything you put in the fridge. The less air that gets to the food the less oxygen available for the mold to grow. Also, the less airborne mold that can get to it in the first place. So, use a snap lid or plastic wrap. Just don’t put an open bowl or plate in the fridge – that’s a recipe for moldy leftovers.

The sooner you can eat leftovers, the better. The maximum most health inspectors will allow restaurants to keep leftovers is three to four days. After that you may risk serious and life-threatening food poisoning. A simple way to keep track is to label food that goes in the fridge. Save your memory for more important things than keeping track of meatloaf.

Have some masking tape and a marker handy in a drawer in the kitchen. Just tear off a piece of tape and stick it on the container. Either write the date on the tape or just give the container an ID number. Then on a piece of paper on your fridge door write the ID number followed by the date stored, the due date and the contents. This way you don’t have to rummage through your fridge but just glance at a simple list on the door to know what’s in there and when it needs to be eaten. (This will also save electricity and reduce your electric bill because you aren’t standing there,  with the door open, shopping for dinner).

Reheating Leftovers

This is crucial. After it comes out of the fridge you need to reheat it. If it’s soup, bring it to a boil. Other dishes you can put in the oven or a toaster oven. I’m not keen on cooking with a microwave (it’s where I store my cookbooks) but if you have no other options, it’s better to reheat in a microwave then to eat it cold with live mold. Heating will kill all the mold, bacteria and yeast that has grown on the food since it was made. Again, it won’t destroy the toxins they left behind. Freezing is the only way to prevent that.

Life Without Leftovers

Ideally you want to limit or avoid leftovers altogether. You may be using them already quite a bit for the sake of convenience. I challenge you to try a week without eating any leftovers and see if you feel stronger, healthier and even wiser. You may be surprised how much of a drain they were on your energy. And they probably weren’t as a big of time-saver as you thought. It still takes time to reheat them and wash their storage containers.

In the end, eating freshly prepared is always better – not just nutritionally but taste-wise. Of course, if avoiding leftovers is just not possible for you or too big of inconvenience, then follow the other suggestions to keep them as healthy as possible.

Make it Happen

  1. Avoid leftovers whenever you can. Make enough for one meal and no more.
  2. Freeze leftovers in preference to refrigerating them.
  3. If you do use the fridge makes sure it is as cold as it can be without freezing your food.
  4. Make sure all leftovers are airtight.
  5. Do not eat leftover raw dishes unless you are using a lot of antifungal ingredients like garlic, turmeric or onions.
  6. Reheat cooked leftovers thoroughly before eating.

Questions & Answers

I’d rather not waste food. Isn’t eating leftovers better than throwing food away?

Best is just to make as much food as you need to eat. Don’t fret if you’re just throwing away a little serving. Just make enough for everybody. Leftovers can be fed to animals or put in the compost pile. Don’t treat your stomach like a garbage pit.