It’s no secret that I browse reddit a lot. On the cooking-related subreddits I frequent, food safety questions are common. I see a lot of “I left x out for y hours, can I still eat it?” and “How long will my meal prepped food last in the fridge?” posts. I also see a frightening amount of people suggesting reusing marinades, or suggesting that rice lasts for a week in the fridge. Yikes!

Unfortunately, these things are not taught in school, and unless you grew up with a parent who cooked, and learned from them, it can feel daunting to cook for yourself. I’ve known a few friends my age who avoid cooking meat, or worse, avoid cooking altogether because they don’t trust themselves to do it safely. I hope this post will increase your confidence in the kitchen.

I have been cooking for a long time and if you know me well, you know I’m a germaphobe. I also learned about microbiology and chemistry at university. So you can trust me on this stuff. Here’s everything you need to know about food handling, storage, and safety for total beginners.

Important Concepts

What Makes a Food Perishable?

Why is it that some foods, like dried fruits, can be kept out at room temperature without going bad, while others need to be kept in the fridge?

Bacteria need certain conditions in order to grow. These include a particular temperature, an appropriate pH level (acidity), moisture, and oxygen (for some bacteria). Vinegar is acidic, so despite meeting the other conditions, it can be kept on the counter. The dried fruit we mentioned above has all the conditions except for moisture levels, which is why drying is one of the original food preservation methods.

As for oxygen, many spoilage bacteria are aerobic, meaning they require oxygen to thrive. This is the logic behind vacuum sealing foods. That being said, a vacuum can be the perfect environment for the highly toxic C. botulinum bacteria to grow (yes, the one that causes botulism), so vacuum sealed foods that meet the other conditions must be vigilantly stored at cold temperatures.

If you want to get into any food preservation techniques like dehydration or canning, you need to keep these four conditions in mind, as well as the characteristics of anaerobic bacteria.

The Danger Zone / Bacterial Growth Zone

The reason we keep perishable foods in the fridge is because bacteria grow slowly at refrigerator temperatures, and this preserves the food.

The underlying concept behind this tactic is called the danger zone, or the bacterial growth zone. When perishable foods are kept between 4-60C, or 39-140F, bacteria grow rapidly and food will quickly spoil.

A general rule of thumb is to avoid keeping items in this temperature range for more than 2 hours. After 4 hours, it’s garbage.

The only times perishable foods should be in this zone are during cooking and cool-down (or if you’re intentionally fermenting something or making kefir). Otherwise, stick them in the fridge or “hot-hold” them, keeping them above 60C/140F by using the keep warm function on a slow cooker or instant pot, or simmering on low on the stove.

Of course, if you’re packing a lunch your food will be in this range. But the growth zone gets more and more dangerous the closer to the higher end of the range the temperature gets (bacteria like the warmer temperatures best).

So if your food was kept in the fridge, it will spend some time warming up before sitting at room temperature. Most people are okay with food that’s kept at room temperature for under 4 hours. I know plenty of people willing to keep cooked food out for longer, too, but that’s where things start to get risky.

You can mitigate any risk by packing a cold pack with perishable items, but it’s okay to not be too obsessive about the ol’ brown bagged lunch.

When you really have to worry about this stuff is when food is cooling down to room temperature, as opposed to coming up to it. Some examples are leaving food out at room temperature for serving, and when cooling it off before storage.

Again, keep the 2 hour rule in mind and set a timer for when to put away your food. You can put it away as soon as it stops steaming, but I like to let it cool a little more so it doesn’t make my fridge work too hard.

Do toss any perishables you accidentally leave out on the counter overnight: would you rather the cash value of the food or a fun-filled day of diarrhea? Yeah.

Bacteria vs. Bacterial Waste Products

Some people think that if you microwave something that smells a little off and cook it really hot, it will kill all the bacteria. This fact is true, but the bacteria themselves are not the only thing that can make you sick.

Bacteria release metabolic waste products (basically poop) when growing and multiplying, which can contain toxins. These are not inactivated by cooking. If you consume enough of these toxins, you will become ill.

A common folk rule for identifying when a food has undergone enough bacterial growth to be toxic is whether it smells or not. I have read that the whiff test is not perfect, because some harmful bacteria don’t produce a smell, but they do tend to correlate. What I’ve gathered is that a smell is sufficient for the food being bad, but not necessary.

The way to manage the bacterial waste product issue is to simply avoid eating food that’s more than a few days old, or anything that’s been in the danger zone for too long. And you can use the whiff test as back-up.

Another rule of thumb is that 1 hour out on the counter is equal to a day in the fridge. But I have no idea how accurate this is!

Relatedly, this is the reason you can’t reuse marinades on a new piece of raw meat. They hold on to bacteria from the meat and can quickly reach high levels of bacterial waste products, even stored in the fridge. You can, however, convert the marinade you used for a piece of meat into a sauce or glaze for immediate use by boiling it, as long as you’re not storing it for long after it’s had raw meat in it.

Cross-contamination

Most people have probably heard of cross-contamination before, but don’t know the practical steps to avoiding it.

Cross-contamination occurs when bacteria from one source make their way to another food product, via infected hands, dish rags, cutting boards, or other surfaces.

It’s important to understand that bacteria are everywhere, but the majority of bacteria are not harmful unless they grow enough to produce appreciable levels of toxins.

Still, it is important to avoid cross-contamination. If you eat cross-contaminated food cold or not warm enough, you could ingest harmful bacteria like E. coli or Salmonella.

The best practices for avoiding cross-contamination are as follows.

Prepare raw meats and other perishables separately, using separate knives and cutting boards (or wash them in between uses). Place the meat packaging or eggshells directly in the garbage after moving the food to the prep surface or cooking pan. Clean all surfaces thoroughly after use. Never re-use a cutting board or knife after using it on these items.

I like to prep my veggies first. I’m not too careful if I know I’m going to be cooking them thoroughly — I’ll share a cutting board without a second thought. But if something’s going to be eaten raw it’s a good idea to rinse off the knife and cutting board in between vegetables.

Try to keep track of what’s touched what, and don’t touch anything raw to anything else that isn’t going to be immediately brought up to a safe cooking temperature. It quickly becomes second nature.

Wash your hands frequently. This means after opening the pack of meat and touching anything that could contaminate another surface. On a big cooking day I might wash my hands 15-20 times!

Safe Cooking Temperature

If you don’t have a meat thermometer, go and get one right now. They’re useful for a number of purposes other than just cooking meat, too. Make sure it’s an instant-read, digital thermometer. Waterproof is nice too. Something like this one. The analog ones are, in my opinion, inaccurate and result in over-cooking.

Make sure to check it in a few places, and check pieces in different parts of the pan to ensure they all cooked evenly.

Health authorities have developed a range of safe cooking temperatures for different perishable food products, which I’m pretty sure is based on what bacteria are most likely to be present on that kind of item. For example, salmonella is found in chicken, so chicken needs to be cooked at a temperature that would kill that particular bacteria.

If you don’t care to memorize a bunch of different temperatures, and don’t mind your pork chop being a little overcooked, you only need one magic number: 165F/74C. If you get a reading of 165F/74C when measuring the thickest part of the meat in the centre, it’s done.

This is the highest minimum recommended temperature for cooking, and it is recommended that riskier meats like chicken and ground beef be cooked to this temperature. Ground beef must be cooked thoroughly because it is ground, and could potentially have bacteria throughout. So rare burgers aren’t a good idea unless you know the meat is good quality and has been recently ground, and even then, ehhhhh.

Of course, you can and should eat red meat steaks rare! As long as the outsides are cooked thoroughly, a rare steak is safe to eat. This is because bacteria cannot penetrate the structure of red meat.

By contrast, bacteria can be anywhere in chicken so chicken cannot be cooked rare and must always be cooked all the way through.

The temperatures on the chart are instant-kill temperatures. It means that if the food hits that temperature for even 1 second, the bacteria are safely killed off. However, you can hold food at slightly lower temperatures for longer to achieve the same effect. This is irrelevant to most home cooks, but it’s why you can cook chicken breast by holding at 150F in sous-vide cooking. Some older slow cookers were also developed to exploit this principle, but nowadays, they all heat the food over 165F.

Is it Still Good?

Knowing whether a food is still safe to eat involves knowledge and intuition, but you can get by with just the knowledge part.

I have eaten some questionable items in my life, but as conscientiousness increases with age, I find myself being a little more discriminating. I think 4 days for cooked foods is definitely reasonable, and I’ve pushed that to about 7 days before, but I’d recommend just eating stuff within a few days or freezing it.

If I’m ever unsure how long something lasts, I use stilltasty.com. I find it’s pretty accurate. As a side note, eatbydate.com is not accurate. It says chicken is good for 3-5 days after the best before date, which is not true… it’s just good for 3-5 days, period. Just avoid that website, as it can trick you into thinking best before dates are all nonsense.

In reality, best before dates are a useful approximation. If you follow them dogmatically you’ll do just fine. But you can definitely still eat some stuff past its date. I have a good friend who always says, “it’s best before, not toxic after!”.

Unopened things are often good a little longer, and milk and yogurt are definitely good for a while past the date. But don’t risk it too much, and look for signs of spoilage.

General signs of spoilage include a slimey texture, an off odor, mold, wilting, or any unusual change in how a food normally appears to the senses. You can always google “how to tell if x is bad”.

How to Clean your Kitchen

Cooking and cleaning go hand in hand. If you want to avoid cross-contamination, you’ll need to clean up along the way.

You’re going to want to do the dishes. I recommend doing them as you go but if you have a dishwasher you can just load them in there. If you’ve prepped meat, make sure to do a thorough job washing whatever touched the meat. Regular dish soap and hot water will remove the bacteria effectively.

Afterward you should clean and sanitize your sink, but I don’t always do this. I only use my sink for dirty dishes that get washed with hot soapy water, so it’s not too terrible.

When I do sanitize the sink, I like to use bleach, especially if I’ve prepped a lot of meat or have reason to believe my sink and counters need a good cleaning. I just fill the sink with water and add a capful of bleach. That’s all you need to kill everything! You can dip your dishes in the solution as well, but don’t mix bleach with any other chemicals, especially vinegar (and while we’re on the topic, toilet cleaner).

Vinegar is another reasonable choice as it kills most bacteria and it’s generally mild. Lysol is a heavy duty product that kills as well as bleach but has a strong scent. And some people simply wash their sinks and counters with hot soapy water; this is effective as well.

As a side note, your sponge can be a source of cross-contamination. As a rule of thumb, it shouldn’t smell bad. If it starts to smell, either throw it out and get a new one, or refresh it by soaking it in boiling water, microwaving it wet until hot, or soaking it in a diluted bleach solution.

Common Myths

Myth: boiling kills all germs

Boiling does kill all live bacteria. But importantly, it doesn’t kill the spores, from which they can grow back, and there is bacteria everywhere in the environment.

I have had someone tell me that cooked food lasts forever because it has no more bacteria due to being boiled. Um, nope.

When you put cooked food into a container, the container has bacteria on it. Usually they’re harmless, but they still produce toxins over time. Even if you sanitize a container before use, there is bacteria in the air. It’s nearly impossible to prevent bacterial contamination of perishable food, and this is why we keep it in the fridge.

If you’re really interested in this, you may be wondering how canned foods are preserved. There are a few important things to know here. Boiling kills all live bacteria, but it cannot kill the spores from which they grow. Botulism grows well in anaerobic conditions, like in a can, so it’s important that canned food be heated to at least 120C to kill both bacteria and spores during preservation.

Water boils at 100C, and a stovetop cannot increase the temperature beyond this under normal conditions. That’s where a pressure cooker comes in. A pressurized environment allows water to reach much higher temperatures, enabling the safe preservation of canned goods. It also cooks things faster, which is why I own one.

But, you may be thinking, didn’t grandma always make her jams in a hot water bath? Certain recipes are safe for home canning at boiling temperatures because they achieve a pH where botulism growth is impossible. Still, you need to follow specific canning recipes as they’re designed to achieve a certain pH for this reason.

It all comes back to those 4 conditions bacteria need to grow.

Myth: you don’t have to worry about vegetarian food

Some people think vegetarian food can never grow bacteria because it doesn’t have any meat. This isn’t true. If it gets cross-contaminated it can make you just as sick as any meat dish. Ever heard of listeria contamination in spinach? Yeah, that happens.

Stick to the rules, even if the food doesn’t contain meat. Bacteria can definitely thrive in vegetarian food!

Relatedly, properly stored and cooked meat is perfectly safe to eat. Food safety is not a good reason to miss out on a great source of protein and iron.

Myth: rice stays good for a week

Okay, I am guilty of this one. I used to meal prep rice dishes and keep them in the fridge for a week. But then I heard of rice poisoning, so I try to freeze rice now if I’m not going to eat it within a few days.

Here’s the deal: rice contains bacterial spores that are not inactivated through cooking, even if you boil it (see myth: boiling kills all germs). These spores can spawn a bacteria called B. cereus which produces toxins that make people ill in sufficiently high quantities.

The bacteria grows in the growth zone, but importantly it also grows slowly in the fridge. So leaving rice in the fridge for a while can cause B. cereus to grow. The creepy thing is, B. cereus doesn’t make a smell. So you can eat those 3 day old takeout leftovers without noticing a thing, until you don’t feel so great.

It’s not a huge risk or anything, but why risk it at all? Now that you’re aware you may as well treat your rice right.

If you pressure cook your rice using a stovetop pressure cooker (higher pressure than an electric one like the instant pot), you can inactivate B. cereus spores. But for the rest of us, avoid leaving rice at room temperature, and keep it in the fridge for 2-3 days, otherwise freeze it.

Myth: you can slow cook kidney beans

Well, you can slow cook kidney beans, but you need to boil them for 10 minutes first. Raw kidney beans contain a toxin called phytohaemagglutinin which is actually made more potent by slow cooking temperatures! If you make this mistake, you could end up very sick and very sorry. Boiling for 10 minutes inactivates the toxin so you can safely slow cook the beans.

Myth: you should rinse raw chicken

Some recipes add in a totally unnecessary step where you rinse your chicken before cooking it. While it may help remove some excess bacteria, it’s also going to dirty your sink and increase your chances of cross contamination.

There isn’t much net benefit to rinsing chicken (unless it’s smelly, I believe, but I would just throw it out in that case), because the bacteria that would be removed by rinsing will be killed by proper cooking.

If you must rinse your chicken, clean out your sink after.

Conclusion

A seasoned cook will have all this knowledge stored intuitively in their head, and the whole process becomes second nature.

You prep your veggies and meats separately, wash your hands frequently, clean up well, take the temperature of your foods, and make sure you don’t leave them out too long. You know when leftovers are good, and you know when to toss something!

You might think all this is a little neurotic, or a lot neurotic. I fully admit my feelings of kinship with the friends character Monica Geller. But it’s really not that hard and it can save you a lot of hardship, and ultimately save you money if you store and prep your food right.

You don’t always need to apply these food handling rules dogmatically. The human body is quite resillient! But having a good understanding should keep you safe and healthy.

Hopefully this increases your confidence in the kitchen. I would love to hear from you below. Let me know if I missed anything or if there’s anything you’d like me to discuss in more detail in a future post.