Spoiler Alert! When Does Food Actually Go Bad?

27:51 minutes

A woman checking if her food is expired. Credit: goodluz, via Shutterstock.

How many times has this happened to you? You’re standing in front of an open freezer, wondering what type of mystery meat has been left in there, when you purchased it, and if it’s still safe to eat? If you’re puzzled by sell-by dates, freezer burn, and just how long food can remain edible, you’re not alone. Studies show that more than 80% of Americans misinterpret date labels and throw food away prematurely to protect their families’ health. That adds up to $218 billion worth of food each year.

Janell Goodwin, with the USDA’s Food Safety and Inspection Service, and Francisco Diez-Gonzalez, professor and director of the Center for Food Safety at the University of Georgia, join Ira for a master class in food microbiology and safety. Then, Roni Neff of Johns Hopkins University Bloomberg School of Public Health explains how confusion over date labeling is worsening food waste and climate change.

And while the USDA states that food that has been frozen is safe indefinitely, your frozen food might not taste as fresh after a few months. Here’s the ideal time you should be freezing your meals:

Frozen Food Tastes Best Within…
Bacon and sausage 1 to 2 months
Casseroles 2 to 3 months
Egg whites or egg substitutes 12 months
Frozen dinners and entrees 3 to 4 months
Gravy, meat, or poultry 2 to 3 months
Ham, hot dogs, and lunch meats 1 to 2 months
Uncooked meat roasts 4 to 12 months
Uncooked steaks or chops 4 to 12 months
Uncooked ground meat 3 to 4 months
Cooked meat 2 to 3 months
Uncooked whole poultry 12 months
Uncooked poultry parts 9 months
Uncooked giblets 3 to 4 months
Cooked poultry 4 months
Soups and stews 2 to 3 months
Uncooked wild game 8 to 12 months

Source: U.S. Department of Agriculture

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Segment Guests

Janell Goodwin

Janell Goodwin is a Technical Information Specialist at the USDA Food, Safety and Inspection Service in Washington D.C..

Francisco Diez-Gonzalez

Francisco Diez-Gonzalez is a professor and Director of the Center for Food Safety at the University of Georgia in Griffin, Georgia.

Roni Neff

Roni Neff is the Program Director for Food System Sustainability and Public Health and an assistant professor at the Johns Hopkins Bloomberg School of Public Health in Baltimore, Maryland.

Segment Transcript

IRA FLATOW: This is Science Friday. I am Ira Flatow. 


AJ: Yeah? 

KATIE: Can you come here and look through what’s in the freezer with me, please? We need to figure out what we’re going to grill. 

IRA FLATOW: How many of you were like Katie and AJ last weekend, rummaging through the freezer to see what’s good to grill, only to come across packages of long-forgotten frozen food and wondering, is this stuff still good to eat? 

AJ: I don’t remember this at all. 

KATIE: What are they? 

AJ: They’re steaks. 

KATIE: What does it say? 

AJ: September 5, 2018. 

KATIE: Would you eat this if we defrosted them? 

AJ: Probably not. 

KATIE: Why not? 

AJ: Because they’re pretty old. And I don’t know how long they were in the fridge. 

KATIE: Oh, wait. Here’s some hamburger. Oh, this is from the last time we had hamburgers– two leftover hamburger patties. 

AJ: Oh, OK. Yeah. 

KATIE: Would you eat those? 

AJ: So that’s like a month or two ago. Yeah, that’s fine. Would you eat those? 

KATIE: Probably not, because they have a little freezer burn on them. 


They don’t look great. It’s like we definitely unpacked them and then put them in this plastic bag, so they don’t look like they would come out looking really great. But that’s more based on taste, not in the fact that I think that these would– 

AJ: Kill you. 

KATIE: –kill me. 

AJ: Yeah. Well, I think they probably just want to make me puke, but yeah. 

KATIE: OK, I guess we’ll put new hamburgers on the grocery list for today’s barbecue. 

AJ: Man, that’s you. That’s not me. 

KATIE: I just think that they looked a little freezer burned, but maybe we’ll check out these steaks. 

AJ: No. You know what? No, I’m not going to. No. Now that you’ve actually tried to get me to eat them, no. 

KATIE: Why? What about them? 

AJ: Their sell-by date was last September. Also, I don’t remember buying them or what they were for. 

KATIE: We got them at Whole Foods. When would we have gone to Whole Foods for that? 

AJ: I mean, I don’t know. Yeah, expensive– really losing. 

KATIE: $17. Wow. Not only are we– is it food waste, but it’s also money. 

IRA FLATOW: Sound a little familiar, huh? If you’re puzzled by sell-by dates, freezer burn, and just how long frozen food can remain edible, you are not alone. Studies show that more than 80% of Americans misinterpret date labels and throw food away prematurely in order to protect their family’s health. 

That adds up to $218 billion worth of wasted food each year. And, yes, it also contributes greatly to greenhouse gas emissions. We’ll get into that a little bit later. But first, we’re going to unpack. See what I did there? The myths of spoiled food– when it goes bad and why. But more importantly, when it doesn’t. 

Here to bring us a different kind of spoiler alert are my guests– Janell Goodwin, technical information specialist with the USDA’s Food Safety and Inspection Service and Francisco Diez-Gonzalez, professor and director of the Center for Food Safety at the University of Georgia. Welcome to Science Friday 

JANELL GOODWIN: Hi, thank you for having us. 

IRA FLATOW: Nice to have you. 




IRA FLATOW: Nice to have you. Janell, you work with the USDA, which inspects meat, poultry, and eggs. You heard our little intro there. Did that sound familiar? 

JANELL GOODWIN: Oh, for sure. I mean, I talk to maybe hundreds of people a year. And that is, by far, one of the most common questions we get. 

IRA FLATOW: So we’ve got to clear up this issue of food in your freezer. First, let’s talk about it. Does it ever go bad if it’s in the freezer? 

JANELL GOODWIN: So it doesn’t. Frozen foods are actually safe indefinitely. And that’s obviously given that they were safe when you put them in there. I mean, you don’t want to freeze molded food and come back and expect it to be perfectly fine once you thaw it. That’s just not going to happen. 

IRA FLATOW: Does it have to be in a deep freeze? Is there a prime temperature you want to hit? 

JANELL GOODWIN: As long as your freezer is set to 0 degrees Fahrenheit or below, it would keep your food safe indefinitely. 

IRA FLATOW: Wow, that’s 32 degrees below freezing. That’s by Fahrenheit. 


So we’ve got that. OK, OK. Dr. Diez, you’re a food microbiologist. So why is the food considered safe if it stays in the freezer? 

FRANCISCO DIEZ-GONZALEZ: Because microorganisms are not going to be able to grow. 

IRA FLATOW: They’re not? Never? They’re just going to stay dormant forever? 

FRANCISCO DIEZ-GONZALEZ: Yes. Well, some of them may die during freezing, but the majority of them will remain dormant and just sitting there. And as long as it continues to be frozen, the microorganisms are not going to grow, and nothing is going to happen to the food. 

IRA FLATOW: As a microbiologist, tell me the difference between food spoilage and food safety. 

FRANCISCO DIEZ-GONZALEZ: Well, that’s a great question. I’m glad that you’re addressing the issue, because there’s a big confusion between spoilage and safety. But the main difference is– just to illustrate, you could have a perfectly edible food that has not been spoiled that could make you sick. So that’s food safety. 

And on the other extreme, you could have a perfectly spoiled food that if you consume, you may not get sick at all. It will depend. The kind of organisms that spoil food may be different from the kind of organisms that make people sick. Sometimes they are the same. In some rare occasions, you’re going to have the same pathogenic organisms that actually spoil the food, but the majority of the cases, you could have completely different organisms. 

IRA FLATOW: Why is it that if we defrost something that’s frozen, we tell you not to refreeze it again? 

FRANCISCO DIEZ-GONZALEZ: Well, I guess because of that possible risk. Once you defrost the food item, then you will open up the possibility for microorganisms to grow. And it depends on the handling of the food. Then by the time you freeze it, as Janell mentioned, they could have gone– already grown and may get to a level that could make people sick. 

IRA FLATOW: Especially, they say if you’ve cooked it, don’t ever refreeze it, right? Janell, what do you– 



IRA FLATOW: What is– with that? 

JANELL GOODWIN: –yeah, I’ll go ahead and chime in here. So basically, like he said, it has to do with the way that you handle the product while it’s obviously thawed and while you cook it. If you handle it safely, we recommend to use leftovers, which is any cooked product, within three to four days. 

Or you can freeze it within three to four days. That would be perfectly safe. And again, that’s if you’re following the four steps to food safety– clean, separate, cook, chill, being very cognizant of how you’re handling your food. That’s very important. And that’s going to be the biggest factor in whether it will be safe or not. 

IRA FLATOW: Our number– 844-724-8255. Let’s get the first question right at the top to Robert in Cleveland. Hi, welcome to Science Friday. 

ROBERT: Hello. 

IRA FLATOW: Hi, there. Go ahead. 

ROBERT: Yeah, I’ve got one for you on canned food. I’ve got several cases of canned turkey that’s about seven years old. What do you think [INAUDIBLE]? 

IRA FLATOW: Yeah, that’s a good question. Janell, how long do canned products– do they last indefinitely? 

JANELL GOODWIN: So they do. And that’s obviously with any food safety rule as long as you’re handling it safely. Now, with cans, you’re like, how can I handle this safely? The best way is to control the environment that it’s in. Here at the USDA, we say, yes, a can that is 10 or more years old– just being a bit exaggerating here, but that is still good. 

If it’s in good condition, it’s technically safe to eat. There are several factors that may limit the shelf life or quality of canned foods. And that’s, of course, extreme temperatures, corrosion, dents, rust, crushed cans. All of that impact how long cans remain safe and at best quality. If your cans are bulging, rusted, leaking, or deeply dented, you don’t want to use them. And they would not last indefinitely. As long as they look OK, they would be safe. 

IRA FLATOW: Yeah, you don’t want to open up a bulging can. 


IRA FLATOW: That has really bad stuff in it. 



IRA FLATOW: Let’s talk about– Diez, what is the exact microorganism that spoils food? Is there one kind of organism? 

FRANCISCO DIEZ-GONZALEZ: No. We have wide, diverse kinds of organism that can spoil food. You talk about any kind of food. You could have bacteria. You could have molds. You could have yeasts. Those are the three major organisms that can spoil food. Yeah. 

IRA FLATOW: Let’s go to phones. More questions. Sara in Columbia, Missouri. Hi, Sara. 

SARA: Hi, my question is about raw onions. A while back, I caught some clickbait article that said once you cut into an onion, that you need to consume it quickly. Because it can even go so far as to make people sick if it’s raw and uncooked, which seemed so weird to me. And I didn’t believe it. But every third time I cut into an onion, I wonder if that’s true. 

IRA FLATOW: OK, onion question. Francisco, you taking it– 


IRA FLATOW: –if you can? 

FRANCISCO DIEZ-GONZALEZ: –I’ll be happy to take it. Yeah, onions are actually one– some of the– among all the fresh vegetables, onions are the kind that is rarely associated with foodborne disease– fresh onions. Now, what you’re describing is whether you cut the onion. And if you let it sit, let’s say, four hours or overnight at the countertop, probably may not be a good idea to come back to it. Because there could be some organisms capable of growing. 

But for the most part, cutting the onion– if you can leave it out there for maybe less than three hours. And nothing is going to happen. You can put it in the fridge. And, yeah, onions– there have been some studies that actually onions have some anti-microbials. That explains why they may not actually be very often– but rarely to learn that there is any case of foodborne poisoning with onions. So I’ll use that. I would say it is definitely– they are fairly safe. 

IRA FLATOW: Cut away on those onions. What about dried food products like flour, and wheat, and things like that, that stay in a container all the time and don’t seem to ever go bad? Is there any possibility they could go bad? 

FRANCISCO DIEZ-GONZALEZ: For the most part, no. They can remain. As you know, you can have your flour in your cupboard for years. You could pick it up. And you can use it fairly well. So in terms of spoilage, dry foods are some of the most stable foods that there are. Of course, if you have high-fat foods such as some nuts, they may go rancid. 

And there’s not going to be much of a safety issue, but a quality issue. But, yeah, the low water protects all of the dry foods. But on the other hand, we’ve been learning recently there are cases of outbreaks with, for example, wheat flour with some type of lower dry foods of bacteria– are capable of surviving for a very long time during storage. 

IRA FLATOW: Wow, that’s quite interesting. Let’s go to the phone to Kathy in Minneapolis. Hi, Kathy. 

KATHY: Hi, thanks for my call. And our local public radio station, Minnesota Public Radio, did a topic on food spoilage about a week ago. And my question is, what is the best way to thaw food? Now, it’s in the summertime. Should– and does it depend on the kind of food, meat versus vegetables, so in the fridge, on the counter, use the microwave? 

And then the other point I was going to make is I went to a wedding potluck– wedding reception a number of years ago. And between the time that the people drove to the church, the ceremony at the church, drove to the park for the potluck, our food was sitting in our hot cars in July for probably three or four hours. 

So my point is that remember the time from when it leaves your kitchen to the time you sit down and eat. Whether you’re at a wedding or a sports game, it’s going to be a long time. And keep your food cold. But anyway, my question was about the thawing, so [INAUDIBLE]. 

IRA FLATOW: OK, let me get– look at Janell who is booing or oohing at that one. 

JANELL GOODWIN: Yeah. I mean, that, again, sounds so familiar, especially in this hot weather as we’re approaching the summer months. So to answer your first question, never, never, never thaw meat, poultry, produce. Whatever has been frozen– we absolutely do not recommend to thaw on the counter. 

That is just not a controlled environment. You run the risk of foodborne pathogens just growing and multiplying rapidly. The best way that we say is to thaw it in the refrigerator. And that’s always because if you decide that something comes up, you can’t make an event, whatever the case may be, you can safely refreeze those products. 

So always thaw it in the refrigerator. If you have time, plan ahead. If you don’t have time, you’re running tight, go ahead and put it in– you can absolutely cook from the frozen state. Let me see that. If you don’t want to do that, you can use the cold water method, which is where you submerge the product in cold water. 

You make sure that you change the water every 30 minutes. That’s a very good, quick, rapid way to thaw products. Or you can thaw in the microwave. I know a lot of folks don’t like that, just because of the quality that comes out with thawing food in the microwave. You’re actually beginning the cooking process. So that answers that question. 

IRA FLATOW: Let me just jump in before you get to the second question to remind everybody that I’m Ira Flatow, and this is Science Friday from WNYC Studios. You can finish, Janell. 


JANELL GOODWIN: Well, thank you. OK, so the second question has to do with the first one as well. Here at the USDA, we have this zone that is called the danger zone. You all have probably heard of it. It’s the range of temperatures or the zone of temperatures between 40 degrees Fahrenheit and 140 degrees Fahrenheit where bacteria grow and multiply rapidly. You want to avoid this. 

You don’t want to keep your food in this zone for more than two hours. And then like you mentioned, if it’s a hot summer day where the outside temperature is more than 90 degrees Fahrenheit, that time reduces to just one hour. And you do want to account for the time of travel time, the prep time. All of that counts in that two-hour rule. So you want to be very conscious of this, especially if you have traveling plans. 

IRA FLATOW: Oh, yeah. We got that. That’s a very good point. Let’s see if I can get a question from Scott in McGregor, Iowa. Hi, Scott. 

SCOTT: Hi, how are you guys today? 

IRA FLATOW: Hi, there. 

SCOTT: I had a question regarding high-sugar foods that tend not to spoil. And I’m thinking of honey, sorghum, molasses. And I’m just really curious as to why their sugar content can be so high with such a liquid environment and not have serious bacteria growth in them. 

IRA FLATOW: Dr. Diez? 

FRANCISCO DIEZ-GONZALEZ: Yeah. Well, sugars are chemical compounds that are capable of dissolving in water at relatively high levels. This is what we call in chemistry the saturation point. So, yeah, you could have perfectly a liquid with a high content of sugar or molasses. And, yeah, you got it right. Exactly. 

The high level of sugars that those products have– they decrease what we food scientists call the water activity. The water content is still pretty high. You would think maybe 30 or 40% of water. But because of the sugar, that water will not be– or microorganisms are not going to be able to use that water for growth. 

So they will be inhibited. And they will remain for– at least stable. Things like honey. You still have plenty of water. If you had that kind of water in other kinds of foods, they may spoil. But in the case of honey, it won’t spoil. Because the food is– the water is not available for the organisms to grow. 

IRA FLATOW: Interesting. We’re going to take a break and take more of your questions. 844-724-8255 is our number. We’re talking with Janell Goodwin and Francisco Diez-Gonzalez. And we’re going to bring on another public health official to talk about food spoilage with us. And so all kinds of questions. You can also tweet us @scifri. 

We’ll be right back after the break. This is Science Friday. I’m Ira Flatow. This hour we are unpacking the myths of spoiled food with my guest, Janell Goodwin, technical information specialist with the USDA’s Food Safety and Inspection Service, Francisco Diez-Gonzalez, professor and director of the Center for Food Safety, University of Georgia. 

And I want to bring on another guest now, who is looking at the connection between date labeling and food waste and how it’s impacting climate change. Roni Neff is program director for Food System Sustainability and Public Health at Johns Hopkins Bloomberg School of Public Health. Dr. Neff, welcome to Science Friday. 

RONI NEFF: Thank you. I’m pleased to be here. 

IRA FLATOW: Yeah, you’re welcome. So what are consumers most confused by when it comes to date labeling? 

RONI NEFF: So there are a lot of things that confuse people. I think previously we had found that the number one and number two reasons why people are throwing away food is concern about food safety and food quality. And often, they are perceiving the data label as an indicator of food safety. And up until recently, that had not been the case. But now, there is a date label that does indicate safety, so that’s a really important step forward. 

IRA FLATOW: So let’s talk about that. Are there certain groups of people more likely to misinterpret these labels? 

RONI NEFF: Yes. We just recently completed a national survey. And overall, there are about 84% of the overall population that are throwing out food based on labels. But the group that is aged 18 to 34 may be most likely to rely on the date labels to discard food. 

IRA FLATOW: So the labels don’t really tell you about the quality of the food. What do they tell you about– why are the labels there? 

RONI NEFF: Oh, they do. They tell you. That’s exactly what they’re telling you is about the quality. 

IRA FLATOW: I guess I meant to say on safety of the food. 

RONI NEFF: Sorry if I spoke wrong. 

IRA FLATOW: No, no. So it’s safe to eat them, but they may not taste as good. 

RONI NEFF: And they may. So often, the labels are set at a point. They’re set at a point before that quality would start to decline. And so even after the date label, there may be– most people couldn’t detect a difference. Or it may be a very small difference in quality. But let me tell you about the new system of date labels, because this is a really positive advance. 

Basically, they’ve set up so that a small number of foods that would be most likely to become unsafe over time, based solely on the time factor, would get a label called “use by.” And then all the other foods would get a label that says “best if used by.” And this is a new industry standard that’s been put out since 2017. And it’s on more and more foods. 

And what this means is that if you see a label that says “best if used by,” you can use your judgment about whether to eat that. You don’t have to throw it out. And that’s on most foods. Most foods are not going to become unsafe before they become quite unpalatable. 

IRA FLATOW: That’s interesting. How is this confusion contributing to food waste? I mentioned how much food waste is out there. 

RONI NEFF: Yeah. And the amount of waste of food is just staggering as you mentioned. And so we tested six different labels. And across all of them, the people who perceived them as having something to do with safety were much more likely to say that they were discarding food based on the labels. 

IRA FLATOW: Wow. And is there a link to climate change here if you have all that wasted food? 

RONI NEFF: Yes, indeed. So globally speaking, the amount of wasted food is so great that if it was a country, it would be the number three greenhouse gas emitter. It’s vast. And in the United States, the amount of greenhouse gas emissions coming out of food that is discarded could be said to be equivalent to about 37 million passenger vehicles– 


RONI NEFF: –worth of greenhouse gas emissions. 

IRA FLATOW: Wow. So why is the labeling system so inconsistent from state to state? 

RONI NEFF: Well, it evolved kind of as a free for all. And so manufacturers could put any label that they wanted onto those food products. But over time, there’s been a real recognition of how problematic that has been and how it’s kind of undermined the basic purpose of these labels, which is to provide information to consumers. 

But if the labels are misleading us, then– and we’re thinking they’re telling us to throw out food when we don’t need to. Then that’s a real problem. There’s also a problem in the other direction, I should say, which is that if you trust that label to keep you safe and you disregard other evidence like, oh, yeah, but that sat out on the counter for overnight, that could also put you at risk. 

So recognizing how problematic this was, there’s been more and more of a push. And there have been several federal policies put out that didn’t yet pass to do this at the federal level. So when industry came together and said, we’re going to put this forward as an industry standard, that’s a really– that’s great. 

Just this week the FDA endorsed the “best if used by” label as well. They didn’t go so far as to talk about the “use by” label for the foods where it’s a safety risk. But at least they’re on board with that. All the same language, so that we can– once we know what that language means, we can use it and as a guide. 

IRA FLATOW: So it’s getting– it’s moving along, is what you’re saying? 

RONI NEFF: Mm-hmm. 

IRA FLATOW: So what do you recommend that people do to check if their food is spoiled? 

RONI NEFF: So the standard things like look at it, smell it, use your senses, basically. And use your knowledge of how it was stored. Was it stored properly? And one of the things I’d say is that when I mentioned that younger consumers may be more likely to misunderstand the date labels, I think it’s even broader than that, that that kind of basic food safety education hasn’t been given out as much in more recent years. 

Home economics classes no longer exist for the most part. And so there’s a need, also, for a kind of cultural shift, and more education, and more communication, and more thinking about the benefits of eating food that may be past that label if it’s a “best if used by” label. Save money, set a good example for the kids, and improve the environment, and have that food. 

IRA FLATOW: Have the food. Speaking of food, we have a lot of tweets coming in about stuff we haven’t covered yet. Well, let me get to those. Pattie tweets, how about yogurt? Always wondered about those dates on the container. As long as it looks OK, is it OK? Who wants to tackle that one? Janell? 

JANELL GOODWIN: So I can. It has to do with the type of organisms and pathogens that are in yogurt. If this was a call that came into the meat and poultry hot line– we get them so often– I would say, for yogurt, if you are a part of an at-risk population, I would not use it past the “best if used by” date. And that’s for just things such as Listeria that can survive in refrigerator temperatures. 

That can make you very sick, especially if you’re a pregnant woman or a young child. So yogurt– you have to be very cautious with. Things like dairy– you definitely want to be cautious with. But if it looks OK and smells OK, typically if you’re a perfectly normal, healthy being, it would be safe. 

IRA FLATOW: Let’s go to the phones– 844-724-8255. Mosha in Newton, Mass. Hi, Mosha. 

MOSHA: Hi, thank you for returning my call. I plan to install a system of a few containers in my kitchen and to drain the container of air and in one case to fill the container with nitrogen. In another case, just to keep the container in vacuum. And I would like to know if the food pathogen would reproduce in such an environment. 

IRA FLATOW: OK, last question. What about his efforts there? 

FRANCISCO DIEZ-GONZALEZ: All right. Let me take this one. 

IRA FLATOW: Go ahead. 

FRANCISCO DIEZ-GONZALEZ: Yes. Well, I’m not sure. So let me see if I understand what you’re trying to design. So you’re trying to have some sort of container that will create what we would call an anaerobic environment. You store food there. Is that– 

IRA FLATOW: Yes. Yes. 

FRANCISCO DIEZ-GONZALEZ: So, OK. Yeah, anaerobic environments. We have pathogens that we are concerned. There are a number of organisms that are actually favored by low-oxygen environments, like eliminating completely– air. We have Clostridium botulinum. Another organism is Clostridium perfringens. 

It would depend on the kind of food that you’re going to be putting there. But those are going to be your two major concerns. And one of the reasons why, for example, canned foods are very safe is because the environment is so tightly anaerobic. But at the same time, they have treated at temperatures to kill Clostridium botulinum. Because otherwise, in the old days– 

IRA FLATOW: It’ll kill– 


–stuff. Yeah. We’ve run out of time. I want to thank my guests– Francisco Diez-Gonzalez, professor and director of the Center for Food Safety, University of Georgia, Janell Goodwin, technical information specialist with the USDA, and Roni Neff, program director for Food System Sustainability and Public Health at Johns Hopkins. Thank you all for taking time to be with us today. 


FRANCISCO DIEZ-GONZALEZ: Thank you very much. 

JANELL GOODWIN: Have a great one.

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Ira Flatow is the host and executive producer of Science FridayHis green thumb has revived many an office plant at death’s door.

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