Getting a mouthful of sour milk when you were craving an ice-cold glass of creamy, fresh goodness is gross, to say the least. And yet, sour cream on a potato? Yum! The whole idea of dairy going bad is subtle and even subjective. When cheddar goes mouldy, we think it's gone bad, while Brie is completely covered in a very tasty, totally edible mould.

In Canada, unless you seek raw milk out from an independent farm, all dairy products are pasteurized, which eliminates the worst pathogens from the product. However, there are a few guidelines that have more to do with flavour and visual appeal. We checked in with our expert, Karen Jull, senior product developer for Loblaw Brands: "I use my sensory discretion; if it's sweet smelling, it's fine. If the container smells mouldy, then transfer the contents to a clean container to confirm -- it might be fine!"

Yogurt, sour cream, crème fraîche, kefir
These products are teeming with life (think gut-friendly probiotics) and are quite long lived, if stored properly. Even so, double-dipping a spoon or dunking a carrot stick right into the sour cream can introduce bad bacteria -- that's cross-contamination -- and the product can spoil.

When any of these products are past their best-before date, employ your senses. Look for mould. Is it all over? Toss it. Just a spot or two? Carefully spoon it out, then with a fresh spoon, taste a tiny bit. Your nose should tell you what your tastebuds can expect. If you don't like the taste, toss it.

Cheese (hard, aged, soft, fresh)
Cheese, especially aged styles, are pretty durable foods. Folks have been enjoying many varieties since well before refrigeration. A little mould on the side was more than likely caused by cross-contamination and can easily be fixed; just slice it off and give the inside cheese a taste. Jull isn't squeamish about mould on cheese: "When there's a slight mould on the outside, you can just cut it off."

Presliced cheeses, deli-counter cheeses
This is where you can run into dairy that goes bad more quickly due to excess handling. Don't buy more than you can consume within a couple of days, keep your cheese well chilled and respect the best-before date. And if you can see bits of deli meat on the cheese you've just been handed, pass it back and look for a deli that has two slicers: one for meat and one for cheese.

Milk and cream
Sniff first, then sip. Sour milk or cream can be used in some recipes. If it's gone so far as to separate and develop lumps, toss it.

Butter, ghee
Butter, as with any fatty product, such as almond butter, can go rancid over time if exposed to oxygen and heat. Salted butter, if kept in the fridge, will most likely not go rancid. If you like it spreadable and keep it on the counter, it may become cultured with bacteria and taste "cheesy" -- a delicacy in parts of Europe. It can be used for frying, if you don't mind the taste. If you don't like the cultured flavour, toss it. Or better yet, melt it down, add wild birdseed, refrigerate to set and put it outside for our fair-feathered friends.

Where dairy products are concerned, let your senses be your guide.