Have you ever taken a big ol’ whiff of rotten milk? It probably smelled like dirty socks or stinky garbage. Blech! But why does food go bad, and how can we be sure that something is fresh and safe to eat?

Join Molly and co-host Rachel as they explore the world of food expiration dates — those little numbers and dates on food packages that help us figure out how old food is! Together, they’ll find out why food goes bad, listen to a rotten egg sing about the power of the sniff test, and learn about the history of expiration dates from Forever Ago host Joy Dolo! All that plus a treat for your ears — an all-new mystery sound!

Check out this food safety chart for more information on how long different types of foods typically stay fresh in the fridge or freezer.

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SUBJECT 1: You're listening to Brains On! Where we're serious about being curious.

SUBJECT 2: Brains On! Is supported in part by a grant from the National Science Foundation.

MOLLY BLOOM: Welcome to the Brains On! Lab or kitchen. This is where we cook all sorts of fabulous foods like my all-time favorite, cottage cheese and mint jello goulash.

RACHEL: Whoa, Molly, that sounds--

GUNGADOR: Delicious!


GUNGADOR: No worry, Molly. No worry, Rachel. Just Gungador, friendly neighborhood, ultimate champion wrestling monster turned dance instructor.

MOLLY BLOOM: Oh, Gungador, you scared us. What were you doing in the pantry?

GUNGADOR: Getting ingredients for expired cereal salad.

MOLLY BLOOM: Expired cereal salad?


GUNGADOR: Gungador have mega corn cereal, thunder crisp cereal, and Gungador's favorite, ballerina bun cereal. Mixed together, the crunchy, sweet, slightly stale salad.

MOLLY BLOOM: But, Gungador, these cereals are pretty old.

RACHEL: Yeah, these ballerina buns were best by last December?

GUNGADOR: Yes. But for food and pantry, expiration date not so important. Like when people say don't wear same underwear two days in a row, it's just a suggestion. Here, have a taste.




MOLLY BLOOM: OK. I mean, I guess I'll try it. Huh, you know, it's not too bad.

RACHEL: Mm-hmm, I guess you're right.

GUNGADOR: Gungador usually right. It's still delicious like eating history.


MOLLY BLOOM: You're listening to Brains On! from APM Studios. I'm Molly Bloom. And I'm here with Rachel from Buffalo, New York. Hi, Rachel.

RACHEL: Hi, Molly.

MOLLY BLOOM: Today we're going to dip into the world of food expiration dates.

RACHEL: Have you ever seen a bunch of tiny numbers printed on the bottom of a yogurt container or maybe a month and year on a bag of bread?

MOLLY BLOOM: Sometimes these strings of numbers look like a strange code or secret message.

RACHEL: But they're not. They're expiration dates.

MOLLY BLOOM: To expire means to go bad or spoil. So the expiration date is the day or month when the food is past its prime. Some say things like sell by, best before, packed on, and June 2024.

RACHEL: And they're designed to help us figure out whether food is fresh and OK to eat.

MOLLY BLOOM: So, Rachel, you wrote in to us with a question about this, right?

RACHEL: Yeah. I wanted to know how do people choose expiration dates for food.

MOLLY BLOOM: Great question. So what made you think of it?

RACHEL: So I watched this video on TED-Ed and it said that for food in cupboards, the expiration dates didn't really matter.

MOLLY BLOOM: Hmm, just like Gungador said.


MOLLY BLOOM: So how seriously do you take expiration dates at home?

RACHEL: Um, for milk, we sniff it or look inside. And when it's rotten, we throw it out. And for like nature bars or anything, we let it slide.

MOLLY BLOOM: OK, so have you eaten food that is past the expiration date?

RACHEL: Oh, yeah. Honestly, it kind of tastes the same.

MOLLY BLOOM: So you were fine. The granola bar is like, yeah, it tastes pretty much the same.


MOLLY BLOOM: So when the milk is bad, how can you tell it's bad? So you say you sniff it. What does it smell like?

RACHEL: It smells sour. But that usually doesn't happen.

MOLLY BLOOM: OK, so it's OK until you smell that bad smell.


MOLLY BLOOM: Very good. Well, yes, those expiration dates can be a little confusing. It's hard to know which ones to listen to. So a lot of our listeners have questions about them, too.

ETHAN: Hi my name is Ethan. And I'm from Powhatan, Virginia. My question is, how do people know when to say something is expired?

ADITYA: Hi, my name is Aditya, and I live in Big Rapids, Michigan. My question is, why do foods expire?

RACHEL: Those are excellent foodie Qs.

MOLLY BLOOM: Agreed. Let's start with Aditya's question about what makes food go bad in the first place.

RACHEL: It all has to do with bacteria and fungi.

MOLLY BLOOM: Bacteria and fungi are teeny weeny living things that you can't see without a microscope, but they're everywhere. They're in the water we drink, the air we breathe, all over our bodies.

RACHEL: And lots of them are actually helpful. In fact, there's good bacteria or fungi in lots of the food we eat.

MOLLY BLOOM: Like yogurt. Yogurt is filled with good bacteria that give it that tasty tang. And when we eat them, those bacteria help keep our guts healthy.

RACHEL: Sauerkraut, kimchi, and kombucha have good bacteria, too.

MOLLY BLOOM: There's also fungi in the foods we eat, like yeast in our bread. That's fungi.

RACHEL: And don't forget mushrooms. Mushrooms are fungi, too.

MOLLY BLOOM: But there's also bad bacteria and fungi out there that could make us sick. And when this stuff gets in or on our food, that's when we call the food spoiled. This can make food mushy, sticky, smelly or covered in colorful fuzzy mold.

RACHEL: Lucky for us there are a bunch of ways to stop bad bacteria and fungi from spoiling our food.

MOLLY BLOOM: One of the best ways to keep those food rotters at bay is to keep food cold.

RACHEL: In cold temperatures, bacteria and fungi can't grow as fast. It's like they are hit with a slow-motion ray. So it takes much longer for them to spread and ruin your food. That's why we have refrigerators and freezers.

MOLLY BLOOM: Another way we can keep food from spoiling is by pickling things. Pickled foods can last years because salt and vinegar make food very acidic. Bacteria and fungi don't like acid, so pickle your produce to make it last.

RACHEL: And then there's drying.

MOLLY BLOOM: Dry foods like raisins don't spoil easily because bacteria and fungi need water to grow.

RACHEL: So if you want to keep food fresh, try drying it out, pickling it or keeping it cold.

MOLLY BLOOM: There are other ways to preserve food. But these are some of the most common. And it's important to do because spoiled food doesn't taste good and can make us sick.

RACHEL: Which is why expiration dates are important. They help keep us safe and let us know when food is at its freshest.

MOLLY BLOOM: Which brings us to Ethan's question.

ETHAN: How do people know when to say something is expired?

RACHEL: Honestly, it would be pretty handy if food could just tell us when it's gone bad.

MOLLY BLOOM: Funny you should say that, because we asked our listeners to invent alarm sounds that rotten foods might make when they're past their prime. Here's what they came up with.

MADDISON: Hi my name is Maddison, and I'm from Los Angeles. And my expiration sound is "Daddy, I am spoiled."

ELLIE: Hi my name is Ellie. I'm from Houston, Texas. And if my food went spoiled I would have a contraption that would go on the food. And if you put your hand near it, it would go like "beep." And if it's not spoiled, it would be like, "ding."

JIWOO: My name is Jiwoo. And if I had a food expiration alarm, then it would be an alarm that said, "don't eat me, don't eat me" and had an alarm sound over and over again until you turned it off.

MOLLY BLOOM: Those are some fantastic food alarms. Rachel, what sound do you think food should make when it goes bad?

RACHEL: Maybe something like a siren.

MOLLY BLOOM: OK, let me hear your siren impression.

RACHEL: Bam-bam, we're rotten and spoiled, bam-bam.

MOLLY BLOOM: Hmm, I love it. Well, food doesn't usually talk or make alarm sounds. But there are other ways foods can tell us they've gone bad.

RACHEL: Like what?

MOLLY BLOOM: When it comes to matters of food safety and the heart I like to turn to my oldest confidant, TV. Let's watch.

TV: Parents, it's dinnertime. Do you know where your foods are? They could be in your cupboard, fridge or pantry going bad. Take a listen to this little snack story to learn the signs of expired food.

BREAD: I used to be a bag of bread hanging out in the fridge alone. But now I'm a bag of bread with friends. So what if they wear leather jackets, sunglasses at night, and smell kind of stinky? They're stylish stinkers, and they're my friends. They're not just one of those bad crowds I've been warned about.

EGGS: Hey, Bread, how are you doing?

BREAD: Eggs, I'm doing great, really great. I was just here saying to myself I'm sure glad I haven't fallen in with a bad crowd.

EGGS: Us, bad? [LAUGHS]

Here's the thing, buddy boy, we're not bad, we're rotten.

BREAD: What?

EGGS: Yeah, it's hard to tell with eggs. One way to know is by putting me in water. If I sink in fresh cold water, I'm good. But if I float, I'm rotten. And let's just say [LAUGHS] these eggs haven't seen the bottom of a pool in years.


STEAK: It's not just eggs.

BREAD: Not you too, Steak.

STEAK: Yeah, I'm bad to the T-bone. You can tell because I'm sticky, tacky, and slimy.

BREAD: I just thought you had a clammy handshake. You, you've all gone bad.

EGGS: We've gone bad? [LAUGHS] You're just as bad as we are, Bread.

BREAD: Me? No. I'm fresh from the top of my crust to the bottom of my crumb.

EGGS: Really? Then what's that spot of mold doing there? [LAUGHS]

BREAD: No! How could I have missed this many signs? I mean, who wears sunglasses at night anyway?

EGGS: Yeah, or you could have just used the smell test.

BREAD: The smell test?

EGGS: Use your nose.

(SINGING) When there's a query if foods like meat or dairy are still good or too scary, take a sniff, take a sniff, take a sniff, take a big old whiff. Inhale the smell and wonder before you blunder. Take a sniff. Trust your schnoz. I know best. Better yet, I "nose" best and here's a cheesy tale to help me prove it.

Gertie got the Gouda. Greedy girlie grabbed the grubby Gouda. Gertie got the Gorgonzola. Where she got it just might fool you. And when grilled, she got moody. Took a whiff and the scent threw me because Gertie's grubby Gouda smelled like super duper booty.


Take a sniff, take a sniff, take a big old whiff. Inhale the smell and wonder before you blunder. Take a sniff.

BREAD: You're saying smelling food is one way to see if it's good or not?

EGGS: Yes, the nose knows. And my little bready buddy, you stink.

BREAD: No! Eh, whatever. Hey, rotten food, let's go stink up the back of the fridge. Last one there is a rotten-- whoops, sorry, Eggs.

TV: So there you have it. Who knew the nose was so good at identifying food spoilage.

MOLLY BLOOM: There are many signs that food has gone bad. If you smell some funk in your food, don't eat it.

RACHEL: Yeah, the nose is a powerful food funk detector.

MOLLY BLOOM: But, and this is important, sometimes food goes bad without smelling foul at all. There are certain bad bacteria that leave no smell and can make you very sick.

RACHEL: You often find these on produce like fruits and vegetables and also on meats.

MOLLY BLOOM: That's why it's important to always wash your fruits and veggies and make sure you fully cook your meat. We'll dive into more rules on food safety in a second. But first, let's switch from the nose to the ears because it's time for the--

SUBJECT 3: (WHISPERING) Mystery sound.

MOLLY BLOOM: You ready, Rachel?

RACHEL: Yes. Here it is.


MOLLY BLOOM: What do you think?

RACHEL: I think it's like plates dropping and rolling around.

MOLLY BLOOM: OK plates dropping and rolling around. What is the scenario that you're imagining? Where the plates might be dropping and rolling on a table, on the floor? What's happening?

RACHEL: Maybe bowling. They're rolling the bowls on the floor.

MOLLY BLOOM: OK, we're bowling with plates.


MOLLY BLOOM: I love that idea. Sounds potentially dangerous. It could shatter. But that's OK. It's an adventure sport.


MOLLY BLOOM: I like it. I like it. Well, we're going to hear it again. Get another chance to guess and hear the answer after the credits. So stick around.

Hi, Brains On! besties, we are composing an episode about stringed instruments and how they all make unique sounds, from ukuleles and sitars to violins and guitars. For this episode, we want you to send us your own version of the Brains On! theme song-- you know-- [HARMONIZING] You can play it on the piano, bang it on a drum, strum it, beatbox it, show us how you sing it. However you want to do it, we would love to hear it.

You don't have to play the whole thing. You can add your own flair, improvise, embellish, write lyrics. We can't wait to hear what you share. Rachel, what would your musical rendition of the Brains On! theme song be?

RACHEL: Maybe something like-- [HARMONIZING]

MOLLY BLOOM: Ooh, I love it. So you also play viola and piano.


MOLLY BLOOM: Which instrument do you think would be better suited for your cover?

RACHEL: The piano.

MOLLY BLOOM: OK, I love it, or maybe you could record yourself doing it both, the piano and then viola. An all-Rachel band, that would be great. Well, listeners, we want to hear from you. Please make a recording of the Brains On! theme song and send it to us at brainson.org/contact. While you're there, you can send us a mystery sounds, drawings, and questions.

RACHEL: Like this one.

SUBJECT 4: My question is, why do bees make a buzzing sound?

MOLLY BLOOM: Again, that's brainson.org/contact.

RACHEL: Keep listening.

SUBJECT 5: Brains, brains, brains on.

RACHEL: You're listening to Brains On! I'm Rachel.

MOLLY BLOOM: And I'm Molly. And today we're talking about food expiration dates which help us figure out if food is fresh and safe to eat.

RACHEL: Food spoils and bacteria and fungi grow like whoa.

MOLLY BLOOM: It's important to stay away from rotten food because it won't taste good and it can make you sick.

RACHEL: But luckily, there are lots of ways to tell if food has gone bad. Rotten eggs float, bread grows mold, and meat gets sticky, tacky, and slimy.

MOLLY BLOOM: And there's the sniff test. If your food smells yucky, steer clear. There's also a list of helpful guidelines from scientists for how long different types of foods typically stay fresh in the fridge or freezer. We'll put a link to it in our show notes.

RACHEL: So if there are lots of ways to tell a food has gone bad, why do we have expiration dates?

JOY DOLO: It's a long and storied story. Joy Dolo, history buff and host of Forever Ago!, the hilarious history podcast for the whole family.

RACHEL: Available wherever you listen to podcasts?

JOY DOLO: 'Tis I. Hi, Molly. Hiya, Rachel.

RACHEL: We're so glad you're here.

JOY DOLO: Me, too. I'm a big time food fan. We've done a bunch of food-themed episodes on Forever Ago. We've got episodes on the history of mac and cheese, chewing gum, ice cream flavors.

MOLLY BLOOM: And don't forget the one about sandwiches. We tasted some pretty wild historical sandwiches for that episode.

JOY DOLO: Yeah, sandwich love forever. And food expiration dates are a favorite topic of mine. Did you know expiration dates have only been around for about 50 years? My grandparents grew up without them.


JOY DOLO: Yeah. That's because for a long time throughout history, the way we got our food was really different than how most of us get it now. People lived much closer to where their food came from. Most people either grew their food themselves or got it from farms. People might have also hunted wild animals like rabbits or deer or gone to a small market. But bottom line, people often knew where their food was coming from.

MOLLY BLOOM: So they usually knew how old their food was.

JOY DOLO: Precisely. Take for example, this imaginary farmer from Ohio in 1824. This was before electricity in homes, so no refrigerators.


FARMER: Time to put some grub on the table. First stop, the root cellar for some taters from the garden.

JOY DOLO: A root cellar is like a basement room that's always cold and dark. Since refrigerators didn't exist, they helped keep foods like potatoes and carrots fresh.

FARMER: Next up, salted pork.

MOLLY BLOOM: Salting is another way to preserve food. People used to put tons of salt on there meat to make it last longer like jerky. The salting dries stuff out, which makes it hard for bacteria and fungi to grow.

FARMER: And for the finishing touches on this delectable dinner, fresh tomatoes from the garden. Let's go pluck them from the vine.

JOY DOLO: Tomatoes fresh off the vine sound divine. But as time went on, more and more people moved away from farms to cities. And they started to lose track of where their food was coming from. At the same time, refrigerators were invented and preservatives entered the picture. Preservatives are chemicals that can be added to food to keep them fresher longer. Together, refrigerators and preservatives made it possible for companies to freeze and package more types of food and make it last.

RACHEL: For the first time, food could travel across the country and even the world and stay fresh.

MOLLY BLOOM: And this made it possible for people to get their food from big grocery stores like the ones we have today.

JOY DOLO: Which brings us to the early 1970s. So in the early 1970s, bell bottoms were in and so was activism. People were protesting a lot, demanding equal rights for all people and marching to save the planet. And they were also demanding more information about their food.

MOLLY BLOOM: Like this imaginary shopper in Los Angeles in 1972.

SHOPPER: Hmm, should I have chicken for dinner? How fresh is this stuff? The meat looks a bit gray. Ugh. Or maybe some rice? Wow. This box is way back on the shelf. How long has it been sitting here?

JOY DOLO: People didn't know where their food came from or how long it had been on the shelf. So store owners and food manufacturers around the world started adding expiration dates to food packaging.

RACHEL: And things haven't changed much since.

JOY DOLO: But here's the thing about expiration dates. In the US, there aren't any laws or rules companies need to follow. That's partly why you could see all kinds of different messages from "best buy" to "use before." And get this, foods aren't even required to have expiration dates.

MOLLY BLOOM: And these dates are not always based on food safety science. The only food that's always tested to see how long it will last is baby formula.

JOY DOLO: Lots of other expiration dates are based on something called shelf life studies, where researchers test each food to figure out how long it stays good. They look at all different factors from how food smells and tastes over time to how much bacteria grows in it.

MOLLY BLOOM: But even with all of this research, it's tough to perfectly predict how long every food will stay good. So most expiration dates are just best guesses, which means we often throw perfectly good food away because we think expiration dates are always right when they're not.

RACHEL: Actually, about 20% of food waste in the US happens because people aren't sure whether to take expiration dates seriously.

JOY DOLO: So next time you go to throw away some bread or cereal because it's past its best by date, wait. Check the handy dandy food storage safety chart we've got in the show notes. And if you're still not sure, use your schnoz or take a close look because it might still be good.

RACHEL: Speaking of expired cereal, I kind of want to try gangadhar's expired cereal salad.

GUNGADOR: Did somebody say expired cereal salad?


RACHEL: Expiration dates are usually guesses that help us figure out if food is fresh and safe to eat.

MOLLY BLOOM: There aren't any official food expiration date rules, so it's good to think of them as guidelines or suggestions.

RACHEL: And they were invented because a lot of people no longer live near farms or where food is produced.

MOLLY BLOOM: So they help us determine how long items might have been sitting on a shelf or in the refrigerated section of the grocery store.

RACHEL: And remember, our senses are powerful. They can help us determine if something is still good to eat.

MOLLY BLOOM: That's it for this episode of Brains On!

RACHEL: This episode was written by Rosie duPont and Aron Woldeslassie. It was produced by Molly Bloom. Our editors are Sanden Totten and Shahla Farzan. Fact checking by Nico Gonzalez Wisler.

MOLLY BLOOM: We had engineering help from Derek Ramirez, Rich Ells, and Brian Frederick with sound design by Rachel Breeze. Original theme music by Marc Sanchez.

RACHEL: We had production help from the Brains On! universe team, Anna Goldfield, Nico Gonzalez Wisler, Ruby Guthrie, Lauren Humpert, Joshua Ray, Marc Sanchez, Charlotte Traver, Anna Weggel, and Aron Woldeslassie.

MOLLY BLOOM: Beth Pearlman is our executive producer and the executives in charge of APM Studios are Chandra Kavati and Joanne Griffith. Special thanks to Ju-yong Park and Hyung-sik Seo.

RACHEL: Brains On! is a non-profit public radio program.

MOLLY BLOOM: There are lots of ways to support the show. Subscribe to Brains On! universe on YouTube where you can watch animated versions of some of your favorite episodes or head to brainson.org.

RACHEL: While you're there, you can send us mystery sounds, drawings, and questions.

MOLLY BLOOM: OK, Rachel, are you ready to hear the mystery sound again?


MOLLY BLOOM: Let's hear it.


What do you think?

RACHEL: I think now I've kind of changed my mind. I think they're putting down the plates on a table and then maybe rolling something else.

MOLLY BLOOM: Very good. So maybe, like, setting the table.

RACHEL: Mm-hmm.

MOLLY BLOOM: Excellent. What do you think they could be rolling?

RACHEL: Maybe sauce bottles.

MOLLY BLOOM: Ooh, yeah. They're like, here, pass the soy sauce. You're like, sure, then you roll it across the table.

RACHEL: Mm-hmm. Yeah.

MOLLY BLOOM: Perfect. That seems like a very innovative way to pass a bottle of sauce. I love it. Should we hear the answer?


MOLLY BLOOM: OK, here it is.

ALLISON: Hi, my name is Allison. That was the sound of me putting plates on a table.

MOLLY BLOOM: Excellent work. You got it.


MOLLY BLOOM: How do you feel?

RACHEL: It feels good.

MOLLY BLOOM: Excellent work. Do you usually get the mystery sound right when you listen?


MOLLY BLOOM: Well, this is a special day.


Now it's time for the brains honor roll. These are the kids who keep the show going with their questions, ideas, mystery sounds, drawings, and high fives.


We'll be back next week with an episode all about Antarctica.

RACHEL: Thanks for listening.

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