Cheerios will no longer be labelled "gluten free" in Canada, CBC News has learned.

Manufacturer General Mills has confirmed it will voluntarily remove the labels from the cereal boxes sold in Canadian stores "as soon as possible," even though it says the product contains less than 20 parts per million of gluten, which meets the regulatory standard for gluten-free designation.

Boxes of Cheerios currently bearing the gluten-free label aren't being pulled from store shelves. Instead, the Cheerios will continue to be sold and replaced with the new label-free boxes when stores restock, General Mills spokesperson Mike Siemienas said in an email to CBC News.

"The change we are making is simply to remove the gluten-free label from future boxes," Siemienas said. "There is not any health risk with the products currently on the shelf."

But the Canadian Celiac Association has been warning people with celiac disease or gluten sensitivity not to consume Cheerios ever since they were first labelled gluten free in August 2016, expressing concern that General Mills had not disclosed enough detail about its testing procedure to assure the association it was sufficiently guarding against potential gluten contamination.

Gluten 'hot spots'

The disagreement over whether Cheerios can be safely labelled as gluten free highlights the complexities of gluten testing and how to avoid cross-contamination between grains.

Cheerios are made of oats, which are naturally gluten free. However, the grain is at high risk for contamination from gluten-filled wheat, barley or rye unless a strict protocol to ensure the oats are pure is followed — from the farmer's field right through the manufacturing process, said Sue Newell, manager of education for the Canadian Celiac Association.

For example, if a farmer rotates crops between oats and wheat — or farm machinery isn't properly cleaned — oats can become contaminated with gluten before they even get to the cereal manufacturing plant.

An information sheet published by General Mills about Cheerios "going gluten free" says its manufacturing process removes any trace amounts of wheat, rye and barley that may have entered its oat supply at the farm level. But the Canadian Celiac Association said the company uses a mechanical sorting system, and was not confident that it catches "hot spots" of high contamination, where the gluten is not evenly spread throughout the batch.

That means that a sampling test on a batch of oats could show an acceptable result of less than 20 parts per million of gluten, but miss a "hot spot" where the gluten content is higher, said Newell. Those contaminated oats could end up in cereal boxes, putting people with celiac disease at risk of illness if they happened to buy one of the affected boxes.

"The CCA's concern is that sampling program used by General Mills may not be sufficient to detect enough hot spots, given what they have publicly made available about that process," Newell said.

But General Mills stands by its testing process and said Cheerios sold in the U.S. will continue to carry the gluten-free label.

In an emailed statement to CBC News, the Canadian Food Inspection Agency confirmed that the move by General Mills to remove the gluten-free label was voluntary, and said the company had "informed" the agency of its plans in August.

"This was a business decision made by the company and not a directive from the CFIA," the statement said.

Disagreement over gluten testing?

Comments made by both General Mills and the CFIA suggest the decision to remove the gluten-free labels from Cheerios stem from an issue around how products containing oats are tested for gluten in Canada.

Siemienas said the company was waiting for "Health Canada and The Canadian Food Inspection Agency (CFIA) [to] publish a consistent testing protocol for products containing oats."

"We look forward to labelling the Cheerios products as gluten-free once consensus is reached on a consistent testing protocol."

When asked for a response by CBC News, the CFIA said its laboratories "use testing techniques for gluten that are internationally accepted and approved. We are working with GM [General Mills] to better understand their concerns regarding the interpretation of our test results."

Finding the most effective way to test oats for gluten is no easy task, and is still a topic of discussion internationally, said Newell, of the Canadian Celiac Association.

"The challenge is to come up with a sampling procedure that gives you a reasonable likelihood of finding any [gluten] hot spots," Newell said. "There are no hard and fast rules on how to do this."