While many people closely check the best before date on food, in CBC News Calgary’s final installment of our series "Food for Thought" reporter Karen Moxley found those dates are more of a guide than a hard and fast rule.

It’s easy to find best before dates on nearly every item in the supermarket, but experts say science doesn’t play much of role in determining when food will go bad.

"Normally best before dates don't relate to the safety of the food product, it's all about quality," said Lynn McMullen, a food scientist at the University of Alberta.


CBC News Calgary examines best before dates as part of its "Food for Thought" series. (CBC)

"So for the most part it doesn't mean someone will get sick past the best before date."

Mcmullen says manufacturers usually choose best before dates through sensory testing — the old fashion sniff or taste test.

For example, when producers see changes in the product quality 100 days past the manufacture date they would normally put a shorter best before date on it. Typically, the rule of thumb is at least 20 per cent shorter.

But often when consumers have a product that has passed the posted date, it is thrown out and a new product is purchased.

Expiry dates

Of course some products will go bad if left in the back of your deli drawer. Take cheese for example — turns out cutting that piece of mould of a block of cheddar may not be the best practice.

"The best advice for moulds on cheese is to throw the product out — don't cut it off eat it," said McMullen. "One thing with mould is that they can produce mycotoxins, they are potent carcinogens, and actually get into the product itself."

Perishable products like cheese are required by law to have an expiry date, but something like a can of beans, sleeve of crackers or a box of cereal doesn't need to be dated.

"Best before dates and expiry dates are two different animals all together," said Tony Marshall, an organic foods producer in High River.

"Technically if a best before date has passed, probably the worst you are going to see is that the product doesn’t taste as fresh as it did when it was first manufactured or packaged…. It’s more that there could be a loss of nutrients, specifically Vitamin C which is the big one that deteriorates over time."

Marshall said products with mandatory expiry dates, like milk or meat, will have a noticeable rancidity. But he says for most products live by the old saying, "When in doubt, throw it out."

He said the goal of best before dates is to give customers the best possible experience when buying that product.

"All of our products have durable shelf life of over 90 days, so legally by the regulations we're not required to do it," he said. "However, on some of our products we choose to do it because they do over time become stale."

Consumer habits can vary

Lauren Campbell is a strict follower of best before dates. 

"I've drank milk before when it was past, and it was a little bit sour — it was disgusting," she said. "I'm going to end up trusting ... the manufacturer."

She is quick to toss anything in her fridge that's even close to the expiry date.

"When I think of best before date or expiry date ... I think of while after that date it's going to be decomposing, there's going to be mould growing, and for me that just kind of mentally disturbs me."

But the truth is gulping back a glass of milk the day after its expiry date isn't likely to make you ill.

"I think they're a good guide, but it doesn't mean that if today is the expiry date, you can't consume the product tomorrow," said McMullen.