A new label on some of the steaks in your grocery store highlights a production process you may never have heard of: mechanical tenderizing.

This means the beef has been punctured with blades or needles to break down the muscle fibers and make it easier to chew. But it also means the meat has a greater chance of being contaminated and making you sick.

The labels are a requirement from the U.S. Department of Agriculture that went into effect this week.

"Blade tenderized," that label might read, followed by safe cooking instructions: "Cook until steak reaches an internal temperature of 145 F as measured by a food thermometer and allow to rest for three minutes." (Other labels might simply recommend cooking to 160 degrees, which doesn't require a three-minute rest time.)

Why do you need to be so careful about how you cook tenderized meat?

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If pathogens like E. coli or salmonella happen to be on the surface of the steak, tenderizing can transfer those bacteria from the surface to the inside. Since the inside takes longer to cook and is more likely to be undercooked, bacteria have a higher chance for survival there.

And without a label, you can't tell if you need to be especially careful with your steak.

Before labeling became a requirement, the grocery giant Costco voluntarily began labeling its mechanically tenderized beef in 2012, after an E. coli outbreak in Canada was linked to its blade-tenderized steaks. (Lydia Zuraw/KHN for NPR )

"It doesn't look any different," says a spokesman for USDA's Food Safety and Inspection Service. "It's not filled with [visible] holes from the needle piercings."

Mechanical tenderizing is not uncommon: Approximately 2.7 billion pounds, or about 11 percent, of the beef labeled for sale has been mechanically tenderized, according to FSIS. The new labels will affect an estimated 6.2 billion servings of steaks and roasts every year.

And it's not unheard of for tenderized beef to be linked to food poisoning: The U.S. Centers for Disease Control and Prevention has tracked six outbreaks of foodborne illness since 2000 that were linked to mechanically tenderized beef products prepared in restaurants and consumers' homes.

In 2009, 21 people in 16 states were infected with the most common strain of dangerous E. coli, called O157. Nine had to be hospitalized, and one victim developed hemolytic uremic syndrome, a potentially fatal kidney disease. USDA food safety officials connected the illnesses to blade-tenderized steaks from National Steak and Poultry, and the company recalled 248,000 pounds of beef products.

"We need to improve how we tell consumers and the food service workers about the particular risks that would be involved in cooking it so that they can reduce the risk of illness," says Patricia Buck, co-founder and executive director of the Center for Foodborne Illness Research & Prevention, a nonprofit advocacy group.

Buck, who has been pushing for the labeling rule since 2009, says she's "very excited" to see it happening. "I think it's an important step in the direction we need to go."

Even before the label became a requirement, Costco had been voluntarily labeling its meat. According to Consumer Reports, the grocery giant began labeling its mechanically tenderized beef in 2012 after an E. coli outbreak in Canada was linked to its blade-tenderized steaks.

Consumer advocate Buck lost her toddler grandson to an E. coli O157 infection in 2001. "I don't like scaring people," she says, "but on the other hand, people don't really know that these can be really deadly pathogens."

Kaiser Health News is an editorially independent news service that is part of the nonpartisan Henry J. Kaiser Family Foundation.

Copyright 2016 Kaiser Health News.

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