Amidst a massive recall of flour due to possible E. coli contamination, Health Canada is reminding Canadians that it's not safe to eat raw dough, batter or any other product containing uncooked flour.

"Flour is a raw ingredient intended to be consumed cooked," the agency said in an alert issued Tuesday, and consuming even a small amount of contaminated raw flour can make you sick.

Flour can be tainted if grain growing in fields comes into contact and becomes contaminated with E. coli bacteria from soil, water or animal waste.

Baking or cooking will kill any bacteria that may be present, Health Canada said.

Parents of young children should also be aware that many recipes for homemade "clay" or play dough contain raw flour.

Common symptoms of E. coli infection can appear within one to 10 days after contact with the bacteria, and include severe stomach cramps, watery or bloody diarrhea, vomiting, nausea and headache.

Most people get better in about a week, but others can become seriously ill and even require hospitalization. Some people don't get sick at all but can still spread the infection to others.

Hundreds of products recalled

Officials began recalling various Robin Hood brand flour in March, and the list has been growing to include hundreds of flour products including tart shells and pizza dough.

The recalls were triggered by the Canadian Food Inspection Agency (CFIA) as part of its investigation into an E. coli outbreak.

So far, there have been 30 reported illnesses across the country, inclding two-year-old Brian Hermsen of Grand Forks, B.C., who spent four weeks in hospital after eating raw cookie dough made with Robin Hood flour.

Parents of young children should be aware that many recipes for homemade “clay” or play dough contain raw flour. (studio2sim/Shutterstock)

Seven other individuals were hospitalized, the CFIA said. No deaths were reported.

The CFIA said on June 2 that no new cases of illness had been reported since April and it was closing its investigation.

One food safety expert is puzzled by that move.

"What we've failed to do ... is verify the actual source of the E. coli," said Keith Warriner, a food microbiologist at the University of Guelph in Ontario. "If you don't know the source, how can you control it in the future?"

Flour has a shelf life of three years, Warriner said, and it's unclear how much of the tainted flour got into the food system and might be sitting in people's cupboards right now.

He suggests pasteurizing the flour before using it by spreading it out on a flat tray and heating it for about 30 minutes at 375 F.

Pasteurizing flour is also what some companies do in the manufacturing of cookie dough ice cream, although there is no law compelling them to do so.

But if you don't know, Warriner said, "It's not worth the risk."