A KIRO 7 Consumer Investigation exposes meat you don't want to eat.

We first got interested in "sell by" dates of meat back in May, when we were going through people's refrigerators to check food freshness.

After discovering a 5-month-old ham, which had just been purchased at a local supermarket, KIRO 7 Consumer Investigator Bebe Emerman began an undercover quest to see how many other stores are selling old meat.

What she found is troubling.

More Information From The Food Safety And Inspection Service: Call USDA's Hotline at: Listeriosis And Food Safety Tips Color Of Meat And Poultry Food Product Dating Safe Food Handling Practices

When the food in your fridge gets too old, you throw it out. But, as our hidden camera investigation reveals, a surprising number of grocery stores in our area are in no hurry to ditch old meat that's weeks, even months beyond the expiration date.

American food markets are among the most abundant in the world.

We rely on stores to tell us how fresh their meat products are. That's where that tiny "sell by" date comes in. There are many opinions about what it means.

"That means it's the last date the store can have it in the store to sell," said one consumer.

"That it should be consumed by that date," said another.

"If it's kept properly, the meat is still good for a week or so," said a third.

According to the Agriculture Department, this date is about quality, not safety. The meat will simply taste best if eaten before this date.

But how many stores are stocking meat that's past its prime? We went shopping with a hidden camera.

We visited 20 supermarkets all over the Puget Sound region, checking the sell-by dates on a variety of meat products.

Of the 20 stores we visited, nine sold us meat past the sell-by date.

In some cases it was only a few days, like this bratwurst.

This chicken and apple sausage was a bit older, 16 days.

But we were shocked to find these products. They were all purchased on July 9.

Check the "sell by" date on this turkey ham: June 11.

This pickle and pimento loaf? May 27.

And these Ball Park franks: April 21. That's more than 2 and a half months past the last date it was supposed to be sold.

Gayle Allemon is a food safety expert with Washington State University's Cooperative Extension Service.

She says eating old lunchmeat like this might be risky.

"There can be enough listeria in there before the sell by date to cause someone to be sick," Allemon said. "The older it is with these lunch meats, the higher the risk."

Amazingly, though, no laws have been broken here. The dating of meat is voluntary and, according to the USDA, it's just a guideline to tell you when to freeze meat or when to throw it away.

As long as meat remains "wholesome and unadulterated" it's OK to be sold.

"As long as they clearly identify it to the consumer that the product is past the pull date," said Leonard Wonchester of Public Health -- Seattle & King County.

In King County, it needs to be labeled. But in other counties a simple display is all it takes.

So, if dating meat is voluntary, and stores can sell it past -- sometimes way past -- the "sell by" date, who's looking out for you?

"You are, the consumer is," Allemon said. "Be careful, look for those then follow them."

"I think there ought to be a safety date, as opposed to simply an expiration date. How are we supposed to know? We're experts in other areas, not in the safety of meat after a particular date."

Allemon says if you have any doubts about the safety of your luncheon meat, or if you there's someone in the family with a compromised immune system, steam it first before putting it in your sandwich.

And even though the "sell by" date is about quality, food safety experts say if your meat is past it, toss it out.