A recent CBC Marketplace investigation revealed that some Canadian supermarkets are using unethical techniques to sell consumers old food. These tactics include changing best-before dates on fresh or frozen bakery items such as cheesecakes, muffins and pastries that are weeks or months past their best-before date.

Often, that best-before date is the only indication consumers have about whether something is still safe to eat.

But Kate Parizeau, an assistant professor at the University of Guelph, says our reliance on best-before dates as a measure of food safety is misplaced, and it's contributing to a huge environmental problem.

The full interview is available in the audio player above. The following portions have been edited for clarity and length.

What's wrong with Canada's system of best-before date labels on food?

The problem with best-before dates is that they're an indicator of quality, but most people think that they are actually an expiry date and that they should throw food out once it reaches that best before date. It's contributing to a huge food waste problem that we have in this country. In Canada, expiry dates are only used for special diet foods, so things like meal replacements that somebody who's ill might need to use, or for baby formula.

What kind of science goes in to determining these dates?

There's actually a lot of wiggle room here. There was some work that was done by CBC that discovered that for most manufacturers, they actually do a good old sniff test to tell when the quality of the food is starting to deteriorate. Then they reduce that time by about 20 per cent in order to be extra safe. It's not an indicator of bacteria content, and it appears that there isn't a whole lot of science that goes into it. As far as I know, there are rules in place to ensure that manufacturers are using the labelling system, but there's not a consistent standard for how it is applied.

We waste an incredible amount of food in this country and in this world. How much do you estimate is wasted because of that disconnect between what a best-before date actually means, and what people think it means?

We know that about 31 billion dollars' worth of food is wasted in Canada, which is about 30 per cent of what we produce nationally. What we find in our research in southwestern Ontario is that about 80 per cent of people use the best before date as one indicator of whether or not they should be throwing food out. Some work in the United Kingdom estimates that if the best before date was extended by even just one day, that they could reduce food waste at the household level by five per cent. We need to value our food more. We need to appreciate all of the work into it. We need to have a better appreciation of how uneaten food that then ends up rotting contributes to climate change.

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