The process of pasteurisation gets rid of harmful bacteria in milk, but bacteria can still grow, especially if the milk is kept out the fridge for too long. The 'Best-Before', 'Use-Before' or 'Sell-By' dates on milk aren't much of a guide – if it starts to smell or taste sour, that's when to stop drinking it. A sip or two of sour milk, while disgusting, is unlikely to make you ill.

Mould is the only thing to check for when deciding if berries are safe or not (any date on the pack is immaterial). The USDA says to discard soft fruits once they have any mould growth as their high moisture content means they can be contaminated with bugs you can't see. 

Homemade whipped cream should be eaten quickly, not because it could make you sick but because it will lose its texture and no longer be fresh. After being kept in the fridge for a day it will lose its form and become a runny liquid with little flavour. Unwhipped, heavy cream should last around 10 days in the fridge according to the USDA's FoodKeeper App.

Pre-made bagged salads may be pre-washed multiple times, but because they’re handled so frequently they are still prone to getting bacteria, which can include listeria, salmonella and E. coli at the very worst. If you're unlucky enough to have picked up a salad with these in, you can reduce the risk of the bacteria multiplying to levels that will make you ill by using the salad as soon as possible after opening and always throwing away leaves that are past their expiry. 

The USDA's FoodKeeper App says 1-2 days is the maximum recommended time to keep raw chicken in the fridge before cooking. That said, in the USA there is currently no legal requirement for chicken to carry a Sell-By or Use-Before date, stores may add one voluntarily. So if it smells and looks fine and isn't slimy, cooking chicken a little after the date on the packaging is usually OK, as long as you adhere to safe cooking times. Always take care when handling the chicken however, as elevated bacteria levels from the raw meat can still pose a risk of illness if they're spread around the fridge or onto kitchen surfaces.

Fish that isn't fresh or hasn't been subject to proper storage and handling can cause food poisoning. 1-2 days is the maximum amount of time fish should be kept in the fridge before cooking or freezing. Where the packaging suggests a Use-By date, stick to what it says. 

Ground beef is much more likely to cause food poisoning than a lump of steak, as bacteria like E. coli, salmonella or staphylococcus aureus on the outside can get mixed all the way through when the beef is minced. Good refrigeration and consuming with 1-2 days will mean bacterial numbers don't get out of hand so do take note of the Use-By date. But most critical is cooking until no pink bits remain.

Eggs will be safe if refrigerated (or kept constantly below 18°C/ 64°F) and cooked by the date on the pack. Up to 90% of British eggs are produced under the Lion Quality scheme, which means the chicken flocks are vaccinated, so salmonella in the eggs is no longer a problem. Have eggs that are out of date? Egg industry website egginfo.co.uk, says the best before date can be ignored if the egg sinks to the bottom of a glass of water. However, if it floats, it's stale.

Use Before dates on spinach leaves are a good guide, but once they start to wilt don't eat them uncooked. Wilted leaves are okay cooked, but once they are brown or slimy the rule is to not eat them at all. To prolong their lifespan spinach leaves should only be rinsed and dried just before they’re used.

Soft cheese is a prime breeding ground for listeria, so soft cheeses shouldn't be consumed beyond their Use By date. Consume undated soft cheeses from the deli section within 1-2 weeks. Throw away any soft cheese that grows mould at any stage. This also applies to blue cheese and cheeses like brie with a white mould on the outside. The USDA says any mould that is not part of the manufacturing process can be dangerous.

Just as with ground beef, ground pork’s expiry date should be adhered to as it can be the perfect breeding ground for various types of bacteria if not eaten within its expiration. The USDA's FoodKeeper App recommends only keeping it in the fridge for one to two days before eating. Burgers made with ground pork should be cooked thoroughly to 71°C (160°F) to avoid food poisoning. 

You can keep bread until you see any mould growing on the surface, but then it's time to throw it out. You may just be tempted to cut out the mould out, but as bread is a porous food it may be contaminated below the surface with bacteria you can't see.

As painful as it is to throw away something when you haven’t even opened it, especially when it’s pricey, you should always throw away raw, cold-pressed juices if they’ve expired. Fresh juices, including homemade, should only be consumed two to five days after they’ve been made. Raw, cold-pressed juices are unpasteurized and far more prone to contamination by bacteria and yeast.

The curled, edible shoots of the ostrich fern fiddleheads are a Canadian and US delicacy that can cause food poisoning if they’re not stored, prepared and cooked properly. The thoroughly washed fiddleheads can be refrigerated for up to a week, but it's essential to cook them well in boiling water, and not serve raw or undercooked.

As with mussels, oysters should be served as fresh as possible and be alive up until the moment they are shucked. At home don't be tempted to keep them longer than two days after purchase (unless you're freezing). Eating out? Ask to see the “shellfish tag”, which every restaurant or retailer is required to have for each bag of oysters that they purchase. If the date on the tag indicates they were harvested longer than a few days ago, avoid. Plus it's recommended that older people, pregnant women and very young children shouldn't eat raw or lightly cooked shellfish.

In one famous study, scientists opened a 40-year-old can of corn and found that the vegetable looked and smelled perfectly fresh, with nutrition values little changed. While really old cans are probably fine, a rule of thumb is not to stretch beyond 18 months for high-acid canned goods, like tomatoes and grapefruit, or five years for low-acid canned goods (pretty much everything else). Never eat from a can that’s bulging, badly dented or leaky.

The USDA says these firmer vegetables can still be good even with a spot or two of mould on – as long as you cut at least one inch around and below the mould, keeping the knife out of the mould itself to prevent cross-contaminating other parts of the produce. The denser texture of these veggies makes it harder for mould to penetrate.

You can eat peanuts beyond the expiration date if they aren’t soft or rancid. But if there’s the slightest hint of mould, or if the peanuts are discoloured, shrivelled, or the shell is broken, throw them away. That’s because peanuts, especially those grown in Africa and Asia can harbour the fungus Aspergillus flavus, which produces a toxin that causes liver cancer. Imported peanuts must pass inspections so you should be OK, but it still pays to be on the look out for substandard nuts and check the packaging for dates. 

There are no expiry dates to go on with leftovers, but the USDA says leftover pizza slices are good for 3-4 days. That’s as long as you put the slices you can't manage in the fridge (covered) within two hours of them coming out the oven.

Read more: 29 essential things to know about reheating food

Sliced salami, ham and other deli meats are good for three to five days after opening according to the USDA. Whole chorizo and salami can keep much longer if they aren’t cut into (any "Best If Used By" information on these is only a guide). Nor do you have to worry about white mould on the surface of salami – this is a traditional feature and nothing to worry about.

Read more: 38 foods that should never be kept in the fridge

With hard cheese there’s little to worry about ­– the USDA says it can keep unopened in the fridge for six months and three to four weeks after unwrapping. Mould spots on hard cheeses like Cheddar aren’t able to penetrate far into the cheese – both the USDA and Food Standards Agency in the UK say you can cut out a mould spot and re-cover the cheese in fresh wrap.

Read more: Simple things you can do to waste less food