Can I Eat This? Cornell Decodes Food Shelf Life

By Mike Howie

Ever wonder how accurate the dates on packaged foods are? The myriad ways in which they’re phrased don’t help: “best by,” “enjoy by,” “sell by,” “use by.” — there are almost too many to count. But how are these dates determined? What do they really mean? And what might happen if we eat the food after the printed date?

“The dates you see on packages, the vast majority of them, have nothing to do with safety,” said Dr. Martin Wiedmann, the Gellert Family Professor in Food Safety at Cornell University. His research group predominantly works in microbial food safety, studying how the bacteria that can cause food-borne illnesses are introduced into foods at different stages of production — from the farm to the store — and how to reduce the risk of getting sick from the food we eat. Now they’re working to make expiration dates clearer and more meaningful to consumers.

Bringing Data to the Masses

As Dr. Wiedmann explained, most of the dates we see on food only reflect the way the food tastes. After the expiration date, or “best by” date, or however the manufacturer prefers to phrase it, the food simply has a higher chance of not tasting the way it was intended to taste. Some dates reflect food safety — like those on deli meat sliced in the grocery store — but the vast majority of dates on packaged foods are an indicator of quality. If something is past the printed date, it’s not necessarily unsafe to eat — though it can be. There’s just a better chance that you won’t like the way it tastes, or that it’s “spoiled.”

So how are these dates defined, and how do we know if they’re meaningful?

It depends on the food and the manufacturer, but in general, those dates are set conservatively. If a manufacturer thinks a product might last for about 21 days in a refrigerator, they’ll test it. Does it taste good on day 21? What about on day 25? If it tastes all right on both of those days, a 21-day shelf life is reasonable. Perhaps the manufacturer will remove a few days just to be safe, but by considering possible storage temperatures, bacteria that could be present, and other factors, they can calculate a date when customers can still open a product, eat it, and have a good experience.

But a lot can happen over 21 days to affect the shelf life of food. Perhaps it was shipped on a hot summer day in a truck that wasn’t properly insulated, so the inside temperature was closer to 50 degrees Fahrenheit instead of the ideal 40. Perhaps you accidentally left milk on the counter for a few hours before remembering to put it back in the fridge. These things happen, and you can only know so much about how the food you purchase has been stored. “When you open your refrigerator and take that food out,” Dr. Wiedmann said, “you tend to have no idea what happened to it until it got there.”

"The dates you see on packages, the vast majority of them, have nothing to do with safety."

Dr. Wiedmann and his team are trying to change that. They’re working to develop the science and data to dynamically predict shelf life and provide better estimates of when people should eat the food they bought. By adding a time temperature indicator to food packaging, they can roughly track the temperatures at which a product has been stored. That information can then be combined with knowledge of the supply chain to produce a more accurate expiration date — one that reflects the conditions a product was subject to from the time it was harvested on a farm to when the consumer removed it from their refrigerator. The consumer can then access the expiration date by scanning a QR code. And so cleaning out the kitchen can become less of a guessing game and more of a process informed by actual, quantifiable data.

Plus, the smarter QR code labels will help retailers just as much as they help consumers. With better data, grocery stores can make better decisions about how to manage inventory. They could even price their products dynamically based on remaining shelf life. Most of us will move aside the gallon of milk with an expiration date two days in the future because surely there’s one with five or six days of life hiding in the back. But what if that expiring milk were a bit cheaper? It’s still safe to drink, and maybe the customer is planning to use it in two days anyway. Now they have an economic incentive to purchase a product at the end of its shelf life. By providing more data, the labels can help customers save money while simultaneously helping reduce food waste.

Spoiled, Safe, and the Difference Between the Two

Food can spoil for a variety of reasons. For example, the flavor of food will change as microbes begin to break it down. Perhaps it becomes acidic, fruity, rancid, or rotten. That’s natural, and it doesn’t mean that the food is unsafe to eat.

Environmental factors can also spoil food. Perhaps you leave a few beers in clear glass bottles in the sunlight for a day. They’re still fine to drink, but the flavor might be off. That’s why so many people add a lime wedge to their drink — it masks the “skunked” flavor — and why so many beers are bottled in dark glass.

“The problem with food spoilage,” Dr. Wiedmann said, “is sometimes and in many cases it’s in the eye of the beholder.” What tastes great to one person might taste awful to someone else. A delicacy in one country might clear everyone out of a restaurant in another. Food spoilage, as it turns out, is largely subjective, and it’s tricky to define. The sniff test can help you decide if something is spoiled, but it won’t help you determine if something is unsafe to eat.

Food is unsafe when there’s something in it that will make you sick, either mildly with an upset stomach or more seriously, requiring medical attention. This, unfortunately, is where we can become our own worst enemies.

"The problem with food spoilage is sometimes and in many cases it’s in the eye of the beholder."

The best way to keep food safe is to do what we’ve always been told: Follow the storage instructions. Keep cold food cold and hot food hot. Make sure your refrigerator and freezer are running at the right temperatures. Cook your chicken to an internal temperature of 165 degrees Fahrenheit. Don’t eat moldy bread. Simple, right?

But we also have to make sure that we’re handling our food properly. For example, you shouldn’t rinse your Thanksgiving turkey because you’ll increase the risk to every other dish while not actually making the turkey any safer: When you move it from the sink to the roasting pan, you’re likely to drip bacteria-filled water onto cutting boards and utensils you’ll use to prepare ingredients for other dishes — potentially even the veggies you’re planning to chop up and serve raw as an appetizer. It’s mistakes like this that can make it easier to get food poisoning at home than in a restaurant.

While spoiled food is tricky because it’s hard to define, unsafe food is tricky because it’s hard to detect. Unsafe food might taste and smell fine — it could even be freshly picked — but it will still make you sick.

Experts like Dr. Wiedmann and his colleagues can already look at the food in their homes and easily make the right decision about what to do with it. But we’re not all so well versed in food safety. “Now we’re trying to give everyone the same tools and the same knowledge that the experts have,” he said. “That’s really our big-picture goal, and that’s what we’re doing one step at a time.”