Local supermarkets have pulled a flavor of Stonyfield Farm yogurt from their shelves, after the company received complaints of glass or plastic beads in the yogurts. Company officials are not commenting on how the beads ended up in the food.

Stonyfield, based in Londonderry, announced the voluntary recall Friday, in response to customers who reported finding beads of 1 to 3 millimeters, about the size of mustard seeds, in their yogurt.

The recall affects 6-ounce cups of Stonyfield organic fat-free blueberry yogurt, product code 0-52159-00044-8, with these dates printed along the cups' bottoms: April 13, 2008; April 14, 2008; April 15, 2008; April 25, 2008; and April 26, 2008.

Carmelle Druchniak, a spokeswoman for Stonyfield Farm, said the company was not releasing the number of complaints or what geographic area they came from. She would not say whether any complaints had originated in New Hampshire.

Druchniak also would not say how the beads got into the yogurt. "We're still looking at the information we have and investigating," she said.

The recall was national and affected both natural food stores and major grocery chains, Druchniak said, but she would not say how much yogurt had been recalled. The company said there have been no injuries reported, and the problem is not believed to be widespread. The Food and Drug Administration posted the information on its website as a recall by the company, not by the FDA.

Locally, the recalled brand of blueberry yogurt was sold at Shaw's, Hannaford and Market Basket stores in Concord and surrounding areas, according to Stonyfield Farm's website.

None of the Concord stores reported any incidents. Spokesmen for Hannaford and Market Basket confirmed that their New Hampshire stores stock that type of yogurt and said that all of it had been removed. Neither knew how much yogurt had been pulled from the stores or whether any had been sold.

Spokesmen for the two Shaw's stores in Concord said that at the time of the recall, none of the yogurt had been in stock.

At Concord Cooperative Market, grocery manager Nick Schneider said the market sells that type of yogurt but did not have yogurt on the shelves from any of the particular batches that were recalled. He did not know if any was sold.

Gary Hirshberg, Stonyfield Farm president and CEO, said in a written release that consumer welfare is the company's top priority.

"While we continue to investigate these complaints and believe that the risk of injury is extremely remote, we feel that this voluntary measure is the prudent and responsible step," he said.

Consumers who have bought any of the recalled yogurt can return open or closed containers to stores for a full refund.

Anyone with questions should contact Stonyfield Farm at 800-PRO-COWS.