U.S. food giant General Mills has announced a voluntary recall of millions of boxes of Cheerios and Honey Nut Cheerios marked "gluten free" because they may contain wheat.
The recall was prompted by the discovery that gluten-containing wheat flour was inadvertently introduced into a gluten-free flour system at a General Mills plant in Lodi, Calif.
Several days of production of the affected boxes occurred in July, with the products distributed nationally before the error was discovered, company officials say.
"Our Lodi production facility lost rail service for a time and our gluten-free oat flour was being off-loaded from rail cars to trucks for delivery to our facility on the dates in question," Jim Murphy, president of the General Mills cereal division, said in a statement.
"In an isolated incident involving purely human error, wheat flour was inadvertently introduced into our gluten-free oat flour system at Lodi."
The gluten could present health risks to people with wheat allergies, gluten intolerance or celiac disease.
General Mills said such people should not consume the Cheerios products involved in the recall.
Consumers can identify Cheerios boxes involved in the recall by looking for a "better if used by" date of July 14, 15, 16 or 17 of 2016 and an LD plant code.
For Honey Nut Cheerios, the dates would be July 12 through 25, with an LD plant code.
The company says it is removing affected products from store shelves and its warehouses.
Customers who purchased affected boxes can contact General Mills at (800) 775-8370 for a refund or a replacement box.
Cheerios and Honey Nut Cheerios produced at other General Mills plants, or products from the Lodi plant marked with dates other than those listed as being recalled, are not affected, the company says.
No other of its cereal brands have been affected, it says.
With gluten-free products becoming more attractive to consumers, General Mills says it is re-organizing its production facilities to make five varieties of the cereal — Cheerios, Honey Nut Cheerios, Apple Cinnamon Cheerios, Frosted Cheerios and MultiGrain Cheerios — gluten free.
