I can be a little paranoid about food safety, but I'm slowly learning the ropes.

I used to be the kind of person who would throw out a whole bag of grated cheese if one piece turned moldy.

Since then, I've learned that expiration dates are more like suggestions, and even food that "went bad" may still be safe to eat.

If you even wondered whether your groceries are still edible, study these tips for 22 staple foods:

1. Sliced meat

Most people don't realize this, but deli meat from the grocery store should only be eaten fresh.

Sliced meat can turn bad in less than a week, even when it's stored in the fridge. Look out for when the pieces turn hard or slimy.

2. Vegetables

Even when vegetables look worse for wear, they're usually safe to eat.

Veggies will lose their bright colors, get soft, and grow mold as they go stale.

But if they're just wilted or a little soft, you can slice off the bad parts. The same goes for green shoots or potato eyes.

Soak the rest of the vegetables in cold water for a few minutes to bring them back to life.

Potatoes are especially tricky: their peels will look nasty, but the spud inside is perfectly healthy. Peel one to be sure before cutting up the rest.

3. Milk

After sitting in the fridge for too long, milk begins to separate and turn rancid. But trust your senses, not the expiry date.

A sharp, sour smell from the carton is a sign that harmful bacteria has moved in.

What you should really be concerned about are lumpy bits floating in the milk. That means it's broken down and not safe to drink.

4. Yogurt

This dairy treat is a lot like milk, and the signs that it has gone bad are very similar.

It can last for weeks in the fridge because of the live bacteria inside, but when it smells bad the whole container is probably spoiled.

When you see a layer of water over your yogurt, it has started to separate and turn bad. Greek yogurt is an exception: it looks like that normally.

5. Seafood

Here's the tricky rule about seafood: it should not smell fishy.

Smelly seafood is rotten, while fresh fish is odorless. Only buy chilled seafood, and prepare it within 36 hours of shopping.

If you're making shellfish, buy them live, and make sure any shells are closed until you cook them (when they open naturally).

Fish with a slippery coating and strong smell is definitely bad.

6. Butter

Do you keep your butter in the fridge or on the counter? Both are safe, but people have strong opinions about which is best.

Either way, keep your butter in a crock or the small enclosure in your fridge door. Too much light will make the cream inside turn rancid.

Of course, salted butter lasts much longer than the regular kind, but after a few months they will both go bad.

The easiest way to spot bad butter is from the smell and taste.

7. Rice

Uncooked rice of all sorts will last for months, especially if you keep it in the fridge or freezer.

Throw out your old rice packages when it starts to get smelly or crunchy.

Leftover rice, however, is a serious health risk. You should only keep it for a few days, and be very careful to heat leftovers thoroughly.

Rice is prone to developing a very dangerous bacteria that can sometimes survive being reheated.

8. Chicken

Poultry is tricky, because the same cut of meat can look very different based on the bird's breed and how it was raised.

Shades of dark, pink, and red meat are all considered normal, but a nasty smell isn't.

Also any chicken that feels slimy or tacky is definitely past its prime.

9. Jams and jellies

Some people worry that a change of color is a sign that their jam has gone bad.

In fact, this is nothing to worry about.

You should be concerned when you spot mold on top of the jar. The whole container should be thrown out, because the entire thing is penetrated with tiny mold spores.

Products with higher amounts of sugar will last longer in the fridge. But leave sugary jam for too long and it can ferment like alcohol, which is also unsafe.

Any time you notice a change in taste, buy new jam.

10. Pasta

It's actually difficult to tell when dry pasta has gone bad. This is one product where you should follow the expiry date.

Even though the pasta usually won't grow mold, it does lose its flavor.

Leftover pasta isn't so hearty: when it changes color, or has sat in the fridge for a few days, toss it.

11. Eggs

You probably heard that if an egg floats, it's not safe to eat. Or maybe you heard that was a myth.

The truth is actually somewhere in between.

Older eggs float because air has seeped into the shell, making a tiny air pocket inside.

Floating eggs aren't always unsafe, but they are definitely stale. You can crack and smell a floating egg to check if it has really gone bad.

12. Red meat

You shouldn't be concerned by a change of appearance, like when meat turns brown or looks shiny.

This is a normal process as red meat reacts to oxygen, and the shine comes from iron and fat reflecting light.

But when meat begins to feel slimy or sticky, you should throw it out. Dark-looking meat is also a red flag.

13. Hummus

Like dairy products, hummus will begin to separate as it ages, with a watery layer forming on top.

It might still be safe to eat. But you should avoid any hummus with a sour taste, which is a sign the ingredients are going bad.

14. Bread

No, you can't "rescue" a loaf with one moldy piece.

Because bread is soft, the tiny spores from one "bad" piece can soak through the entire loaf. Even if you don't see the mold, it's there.

Meanwhile, hard and stale bread is perfectly safe to eat. You can save money by recycling stale pieces in recipes, as toast, or for eating with spreads.

15. Fruit

Every fruit is a little different, so consult the experts about a specific kind.

But for the most part, you can follow your sense of touch. Fruit may be soft, but it should never be mushy.

Fruit skin that is beginning to peel, or feels grainy, is also a very bad sign.

Strange colors and gross smells are also warnings that your fruit is not safe to eat.

But you can cut off bruised segments, and even remove moldy grapes or berries from a bunch. Just make sure to wash the other pieces before you eat them.

16. Non-dairy milks

A lot of families have switched to soy, almond, or other milks that don't use dairy, either because of allergies or for health reasons.

Most non-dairy milks have a very long shelf life before they're opened, but start to curdle in about a week after that.

You'll notice the carton "bloating" as the milk breaks down and gas is released. When you see tiny clumps forming, it's time to get rid of the milk.

But unlike regular milk, if you notice soy milk is just starting to separate, you can shake up the carton and keep drinking.

17. Cheese

This dairy product is very tricky, and it all depends on which kind you buy.

Cheese will start to grow mold as it absorbs moisture, but some cheese will still be safe to eat.

You can cut off the spoiled parts of hard cheeses, like cheddar, and eat the rest. But when soft cheese turns bad, you have to toss the whole container.

Any cheese with a taste like sour milk is also past its prime - even if you don't see mold.

18. Olive oil

First, make sure the olive oil you buy is the real deal, because there are plenty of phony brands out there.

Fresh olive oil should smell like the olives it's made from, light and fruity.

When the oil spoils, it starts to smell sharp and sugary, like glue or oil.

But even if it's separating, the oil can be safe to use. Sometime, you can even pour off the top layer and keep the fresh oil underneath.

19. Peanut butter

When I was growing up, it was normal to keep taking spoonfuls from the same peanut butter jar for years.

In fact, the mixture of oil and fat in peanut butter does keep it fresh, but not forever.

After a few months, you need to get a new jar. When the butter starts to smell and taste different, it's expired.

20. Condiments

Here's another staple that can hang around in your fridge for years.

Sauces like ketchup should actually be switched for a new bottle every six months.

Mustard is a little heartier and can survive up to a year in your fridge.

And for my fellow cheapskates: yes, those condiment packages from restaurants will stay fresh in your cupboard - for a year or two.

If you can't remember when or where you got them, throw them out.

21. Canned food

Yes, canned food can go bad.

To keep food fresh for years, the can needs a perfect seal. Dented, rusty or corroded cans should all be thrown away. They just can't guarantee freshness.

This applies to store-bought food and your homemade canning.

Also: acidic foods like canned fruit or tomatoes will go bad even inside a can (while non-acidic foods like soup don't).

22. Mushrooms

Only keep mushrooms for two weeks before preparing them, and store them in a cool, dark space the entire time.

When these fungi develop wrinkles and dark spots, or change colors, they're not safe to eat any more.