Dan Charles of National Public Radio reports those “sell-by” dates on food are there to protect the reputation of the food. They have very little to do with food safety. If you’re worried whether food is still OK to eat, just smell it.

One of the places that knows most about the shelf life of food is a scientific establishment in Livermore, Calif., called the National Food Lab. At the NFL, they put food on shelves for days, or weeks, or even years, to see how it holds up.

Sometimes, they’ll try to accelerate the process with 90-degree heat and high humidity.

And then, from time to time, they’ll take some of the food — whether it’s bagged salad greens, breakfast cereal, or fruit juice — off the shelf and place it in front of a highly trained panel of experts who check the taste and smell and texture.

The experts give the food grades, in numbers. The numbers go down as the food gets older. Bread gets stale. Salad dressings can start to taste rancid.

John Ruff, president of the Institute of Food Technologists in Chicago, says the companies that sell this food take a look at those grades and decide where they will draw the line, to protect the reputation of their products.

“If the product was designed, let’s say, to be a 7 when it was fresh, you may choose that at 6.2, it’s gotten to the point where [you] don’t want it to be on the market any more,” he says.

“If it’s 6.0, would most people still find it reasonably good? Absolutely,” he says. “But companies want people to taste their products as best they can at the optimum, because that’s how they maintain their business and their market shares.”

This is all organized and carried out by food companies; there’s no federal law that requires dates on any food except for infant formula, although some states do require sell-by dates on milk or meat.

“In 40 years, in eight countries, if I think of major product recalls and food poisoning outbreaks, I can’t think of [one] that was driven by a shelf-life issue,” Ruff says.