A string of flour product recalls this spring has cost the milling sector millions of dollars and costly research may still be needed to find the source of the contamination, say grain industry officials.The outbreak of E.coli 0121 is so mysterious that few people connected to the investigation are willing to discuss it on the record.Fred Jamieson of the Office of Food Safety and Recall at the Canadian Food Inspection Agency “we're working back through the grain supply system to find the answer. We're looking at all sorts of different possibilities.”Among them is the contaminated wheat comes from a particular region of the country or that it's the result of a weather anomaly, he said. He couldn't estimate how long it would take to solve the mystery.CFIA has issued 22 product recall notices covering bags of baking flour, various unbaked pie and tart shells and cookie dough. No deaths have been reported in connection with the recall but the agency said 26 people were initially infected with E. coli and at least six required hospital care. One of the ill people told investigators he still had a bag of flour. It was tested and found to be contaminated with E.coli 0121.The latest recalls were on June 24 and 25 involving tart shells for meat pieces and flour distributed by Ontario firms. The industry hopes the recalls are finished. While a number of small food companies have been hit with recalls, Robin Hood and its supplier Ardent Mills of Brampton appear to have suffered the most.The first outbreak of E.coli in flour occurred in the United States last year leading to a major investigation by the Center for Disease Control. CFIA has inspected all the flour mills in Canada and found nothing wrong in their operations, which makes wheat the main suspect.The mystery deepens when it comes to how the wheat could be contaminated with bacteria most consumers would think of terms of undercooked ground meat.While CFIA says all recalled products should be thrown out or returned to the store, properly cooked bakery products show no trace of the E.coli.Even though little is known of the outbreak, there are reports that a class-action lawsuit is being considered.One theory suggests the E.coli may come from the feces of infected animals or rodents that passed through in the field. But how that would get into the wheat kernals is the subject of considerable speculation.The focus is clearly on raw product and how consumers would ingest it. It could be during cross contamination of food prepared of kitchen surfaces already covered in dough. Another is the use of flour in playdough.All of which points to greater consumer education about being cautious using flour, industry officials say.Cam Dahl, President of Cereals Canada, said, “At this time there is no evidence of the origin of the e. coil. There are a number of source possibilities which do of course include wheat. “There have been a couple of incidences in the U.S. in the past, but this is a rare event,” he said. There's no evidence of any systemic problems.The Public Health Agency of Canada, CFIA and provincial public health partners have worked on the outbreak. “Given that no new cases of illness have been reported since April 2017, the outbreak appears to be over, and the outbreak investigation has been closed,” PHAC says. However it said, “It is not safe to taste or eat raw dough or batter, regardless of the type of flour used as raw flour can be contaminated with harmful bacteria such as E. coli.”coli bacteria “live naturally in the intestines of cattle, poultry, other animals, and humans. Most E. coliare harmless to humans. However, there are many different strains of E. coli,and some varieties can cause serious illness. Although anyone can get an E.coli infection, pregnant women, those with compromised immune systems, young children and older adults are most at risk for developing serious complications.Of the 30 reported illness, 22 were in Western Canada and one in Ontario.As a precaution, people should “not taste raw dough, batter or any other product containing uncooked flour. Eating a small amount could make you sick. Bake or cook items made with raw dough or batter before eating them.”In a report on its investigation of the outbreak in the United States, the Center for Disease Control said the flour that caused the outbreak was produced at a General Mills facility in Kansas City. It did not say what contaminated the wheat. It said consumers should remember “that is it not safe to taste or eat raw dough or batter, whether made from recalled flour or any other flour. Flour or other ingredients used to make raw dough or batter can be contaminated with E.coli and other germs that can make people sick.”Alex Binkley is a freelance journalist and writes for domestic and international publications about agriculture, food and transportation issues. He's also the author of two science fiction novels with more in the works.