Food safety expert Marion Nestle confesses that the oldest spices in her pantry likely date to when she first moved into her apartment — about 20 years ago. While they’re not going to be unsafe to eat, she does add with a chuckle that it’s probably time to throw them out. With the start of a new year, now is a good time to shuffle through pantries and refrigerators to purge old and expired items.

“If you open [a spice] up and you sniff it, and it doesn’t smell like anything, you know, it’s really time to get rid of it,” said Nestle, who is the author of "Safe Foods: The Politics of Food Safety."

When considering refrigerated items, vinegar-based foods are generally safe to keep for a longer amount of time. Nestle hesitates to specify whether “a long time” means a matter of weeks, months or years, however, but says to use good judgement.

“It is fungible because you can’t really tell,” she explained. “It’s very, very unlikely that a high-vinegar product is going to get contaminated with anything that’s going to hurt you.”

That’s because the high level of acid in those foods usually kill most harmful bacteria. But if those pickles are long past expired, and starting to look grungy, then it’s time to toss them.

“You can be a little flexible about high-acid products, but, yeah, [the sell by date] is a pretty good indication that you might want to say, ‘Do I really need this?’” said Nestle.

On the other hand, milk is one item where expiration dates are serious deadlines. In New York City, much milk will often have two dates listed on it.

“The second date is usually shorter, and it’s because if you live in New York, the chances are that milk has been sitting out at room temperature some place between cow and grocery store and it goes bad faster,” said Nestle.

Pre-wrapped foods such as processed cheeses and lunch meats are also some of the first foods that need to be thrown out. That’s because they can harbor dangerous listeria, which is the bacteria that contaminated cantaloupe this past fall, killing 30 people.

“Listeria is the one bacteria that I can think of that is perfectly happy to grow in the refrigerator,” Nestle said.

Leftovers generally keep longer, since cooking brings food to 160 degrees or higher. That makes the food and container in which it was cooked sterile. Nestle also weighs in on the debate on whether food should cool on the counter before being refrigerated.

“It depends on what [the leftovers] are, but I think straight into the refrigerator is always the best idea because that will eventually bring the temperature down a little faster,” she said. “The Department of Agriculture is very strict about what you can do and it advises you to throw away leftovers after three to five days. That seems optimistic to me.”

Nestle admits that she sometimes pushes those limits.

“I think the Department of Agriculture guidelines are very conservative,” she said. “If you follow those guidelines, you won’t make yourself sick from the food. And most food-borne illness doesn’t come from what people do at home anyway. It’s in the food before it gets to you.”

Cutting Board Etiquette

The news about cutting boards, said Nestle, is that it doesn’t really make a difference whether you use wood or plastic. What is important is to keep separate ones for meats and raw foods.

“Cutting boards are only a problem if you’re cutting un-sterile things on them,” she noted. “So the rule about cutting boards is you have to keep kosher: You have one for vegetables and one for meat. And you make sure you that never do raw and cooked foods on the same cutting boards. And you’re supposed to wash them frequently with hot soapy water.”

Also, once cutting boards start to look grungy, it’s probably time to replace them. Of course, “grungy” is relative, so go with your instinct.