Program: Should you cut or chuck mouldy food?

Norman Swan: Tegan, you've got young kids at home. Does food ever lie around long enough to get mouldy?

Tegan Taylor: Yeah, we're bandits in our house for buying bread and then forgetting about it, and then a couple of days later realising that it's bright blue. So I guess…

Norman Swan: That could be penicillin, it could be really good. Do you cut it off?

Tegan Taylor: I feel like we are on the verge of a new scientific discovery. Normally I chuck it out; the privilege of living in a community where we have enough food to go around. But no, I've often looked at, you know, when there's one spot of mould and you're like, oh, surely that's okay.

Norman Swan: You think so? But anyway, this week's What's That Rash? is from a live show that we did at the World Science Festival earlier on this year where we were asking just this question; should you cut mould off food? And What's That Rash? is the podcast…

Tegan Taylor: …where we answer the health questions everyone's asking. This question came from Tilly, which one of our audience members read out for us.

Audience member: Hi Norman, hi Tegan. The question is mould on food. If it's a little bit of fuzz on the outside of cheese, or it's an apple with a fungi forest on the core, is it okay to cut out the affected parts and still eat the food? Or, if this is happening regularly, am I putting myself at risk?

Tegan Taylor: Thank you very much, Tilly, for the question. Before we give you any evidence, what I would like to do is a vibe check. We're going to play a game, it's called 'Cut or Chuck'. Now, I'm going to show you some images…

Norman Swan: 'Chuck' is not vomit, it's actually 'throw it out'.

Tegan Taylor: Well, you haven't seen the pictures yet. I'm going to show you a picture, I'm going to describe what it is, and then I'm going to ask you Cut or Chuck, and you're going to yell out 'cut' or 'chuck'. Let's go. A bit of mould on the edge of a piece of bread. Are we Cut or Chuck? 

Audience: [unclear]

Tegan Taylor: Risk averse. Fuzzy strawberries, Cut or Chuck?

Audience: Chuck!

Tegan Taylor: Same. Mouldy cheese, but not in a good way. Mouldy cheese, but not in a good way?

Audience: Chuck!

Tegan Taylor: Chuck, fair enough. Okay, so we're chucking everything out in the fridge, Norman, nothing's safe. I guess it would be fun to start with just a little bit of…I guess it's biology. Why does food get mouldy?

Norman Swan: Well, first of all, what is a mould? Mould is fungus, and not all fungi create mould. So mould is this sort of powdery, fibrinous growth of the fungal spores on food or in the general environment. So not all fungi produce mould, but there are lots of fungi which do. And some moulds are okay, such as the ones you put in your cheese, Danish blue or whatever you eat. But a lot of moulds (as indeed do many bacteria) produce toxins, or, let's say they produce chemicals, and the question is whether they're toxins or not. That's part of this reaction that we're getting there. And so there's a long history here to mouldy food and trying to preserve it and stop mould occurring on it.

Tegan Taylor: So the thing that gets me about food…so obviously, all that stuff that we just saw was yuck, but there's so many foods that we eat that are delicacies that are covered with mould, like certain types of blue cheese, salami, even the fact that we ferment food to make…I know it's not mould, but fermentation of food…

Norman Swan: Aged beef has mould on the outside.

Tegan Taylor: Right, exactly. And it just makes me think about our really, really hungry ancestor, who was like, 'You know what? I'm gonna risk it.' And then they were like, 'Oh, that's actually really good. We should do that on purpose.' So yeah, we have a long, long history with mould. 

Norman Swan: We do, and kind of a nefarious history too. Do you want to talk about the Mary Celeste?

Tegan Taylor: I am busting to hear this story from you. So, okay, we're talking about mould, we're talking about mycotoxins, so toxins produced by mould, and a particular type of mycotoxin that we call… 

Norman Swan: So this is from a common mould that can grow on rye, and it's called ergot, and in fact ergot has been used clinically. It used to be used to stop bleeding, in fact to induce contractions in labour, it's been used to stop migraine. So it's been used medically. But in an uncontrolled way in contaminated rye, it can actually be taken in such doses that it interferes with the blood supply in your legs, to your skin, causing great pain, and one name for that is St Anthony's fire.

Tegan Taylor: Okay, because people kind of can't keep their feet…

Norman Swan: They're just in agony, and they dance around to get…this is the typical story of St Anthony's fire. So during the plague years, people were starving, they would eat contaminated rye and get St Anthony's fire. So it was a recognised medical problem. And if indeed the story of the Mary Celeste is true, one of the theories for it is that they ate contaminated rye, got ergot poisoning, couldn't stand it, and to douse the pain they jumped overboard.

Tegan Taylor: And that's where this ghost ship was found floating alone.

Norman Swan: So, St Anthony's fire with ergot. Then there's a pervasive toxin called aflatoxin in peanuts, but you also get it in a lot of other crops, and it's a very difficult toxin to control, but we've managed to control it pretty well in rich countries. In poorer countries, not so much. And aflatoxin produces a mycotoxin, which is a carcinogen, as indeed some…there are quite a few carcinogens associated with moulds, and so aflatoxin is one, and liver cancer is one cancer that is associated with aflatoxin, and there may well be other cancers which we're not entirely sure about from other toxins. 

So the problem here (coming back to the question) is if you look at the bread, is that when you see visible mould in soft foods, the tentacles are often going into the food itself. So there have been some studies which suggest that…let's say you've got a package of sliced bread and the first two slices are mouldy, and then you go down, so it's rather than cutting off that, you go down and you will find eventually bread that's mould free, and that's probably okay, there have been some research along those lines. But if you've got a mouldy slice, it's quite likely that the mould is into the bread itself. Whereas those of you who wanted to chuck out the cheese, hard cheese, you can probably safely cut the mould off hard cheese down to what looks as if there's no mould, and there's very unlikely to be mould there, because it's hard and not spreading.

Tegan Taylor: So we're hearing a lot about bad things about mould, but I think we all know that there have been some good things about mould in the past. Any famous moulds that anyone can think of? Penicillin. You think you know the story but I'm going to tell you a chapter that you might not have heard before. So who discovered penicillin? Come on nerds, say it loudly please.

Norman Swan: It wasn't Florey, it was Alexander Fleming. Florey turned it into a drug. 

Tegan Taylor: Okay, so this is it. Alexander Fleming, Scottish microbiologist, we love a Scotsman, a famously messy workplace. And as the story goes (who knows if this is actually true or not), he went on holidays for two weeks, didn't bother cleaning before he went, came back, the place is disgusting, crawling with all sorts of colonies, including mould and bacteria. But when he looked more closely, he realised that the bacterial colonies wouldn't touch the mould. There was like a halo around them. Something that the mould was doing was staving off the bacteria. So he thought there must be some sort of antibiotic substance happening here, and because the mould in question was called Penicillium, he called it penicillin. 

That could have been where the story ended, if it hadn't been for our fave, Howard Florey. We love an Aussie. And so Florey was the one that took Alexander Fleming's discovery of penicillin and started to make something of it. He worked with a biochemist called Ernst Chain to produce penicillin and actually test it. And so they were basically juicing mould. I'm not going to go into how you do that. I imagine it has teats. But they were getting the mould juice, and then they could distil it down and create penicillin.

Norman Swan: In these huge jars.

Tegan Taylor: Huge jars of it. And what was the claim to fame of Florey and Chain, Norman? There was a police officer…

Norman Swan: No, I don't know the story.

Tegan Taylor: Yes, you do, you've told me this story before. Anyway, there was a police officer whose surname was also Alexander. He had nicked himself on a rosebush…

Norman Swan: Oh right, right, right, this is a terrible story.

Tegan Taylor: It is. It's actually a really sad story. He was having an incredible systemic infection. He was on the brink of death. The biologists thought, can we use this as a test to see if our antibiotic works? And it did, and they saved his life for five days, and then they ran out of penicillin, and the man sadly died. And so what this threw up was a question about how to make enough of it. It was war time. Soldiers were dying of war wounds. They were also dying of venereal disease, also treatable by antibiotics. 

And so the part of the story that I suspect you may not have heard of before is the story of Mary Hunt, who is so important to this story, because the problem was that you needed gallons and gallons of penicillin, of mould juice, to yield milligrams of penicillin, what they needed was a more productive strain of mould. So Mary went hunting for a more generous strain of mould, and started scouring shops in her hometown in Illinois for anything with a bloom of mould on it.

Norman Swan: We should explain that in order to make industrial quantities, Florey moved to America.

Tegan Taylor: Exactly, so she was part of this lab. She went to a fruit shop and spotted a mouldy grapefruit and started asking the shopkeeper about it and he was like, 'Shut up, I don't want people thinking…' and she's like, 'Show me where all the mould is.' And he's like, 'There's none here.' Anyway, he did eventually let her into the back room where all of the mouldy food was sequestered, and she found a very slightly mouldy rockmelon. Do you say rockmelon or cantaloupe?

Norman Swan: I say rockmelon. You say tomato…

Tegan Taylor: I say rockmelon too. I don't know why Mary knew that this rockmelon was the one. There was just a faint wisp of mould around the stem of the melon, but she took it back, she cultured that mould, and then she sliced up the rockmelon and fed it to her colleagues for lunch, and they all agreed that it was delicious, but the mould that she collected from the rockmelon was 200 times more penicillin-full than the one that Fleming was using. And so they were able to tweak that strain even more, and that became the strain that went on and helped make penicillin into the factory powerhouse that it is today. Fleming, Florey and Chain shared the Nobel Prize in 1945 for the discovery of penicillin, and Mouldy Mary was lost to history. There you go. So, all hail Mary Hunt.

Norman Swan: Not the first time that that happened, not the last.

Tegan Taylor: Not the last. A forgotten icon of antibiotics. 

Norman Swan: There's an interesting thing about mould as well, which is that it's visible, and when I was in medical school we were always taught you've got to watch for the visible food spoilage, but it's the invisible stuff that can get you as well, such as staphylococcal food poisoning, or salmonella and so on. But nonetheless, the mould is really important, and it triggers a very ancient thing in our brains.

Tegan Taylor: This disgust response, and you see it in animals, they'll have certain hygiene habits, they will avoid certain things. You know, you see animals in a farm yard, and they won't eat the grass where they poo, or cats are super fastidious about being hygienic. Humans are as well, but it always seems more cultural. I'm really interested to know how much of our disgust is something that we've been taught, like, 'yuck, yuck, don't touch that, that's yucky' when we're little, or whether there is something innate to humans about disgust.

Norman Swan: Darwin studied disgust, and he thought it was an evolutionary mechanism that was innate to different animal species, including humans. And there are neurological mechanisms that have been shown. There's a researcher called Paul Rozin who has studied this. So it's innate, and there seems to be commonalities to it. 

So there's a psychologist in Western Australia, Rob Donovan, who's into health promotion and designing health campaigns, and people have used fear a lot in health campaigns, and fear doesn't work that well, but his theory was that disgust works really well. And he was trying to put kids off smoking, so he developed these ads, and what he discovered was there was a commonality about disgust. So one of the ads was a young person smoking, but they pick the cigarette out of the toilet bowl to light, and the kids…you know, blech! And then the other one was somebody smoking, and the cigarette turns into a cockroach. 

Tegan Taylor: Oh!

Norman Swan: It works. 

Tegan Taylor: It's visceral, it comes from deep.

Norman Swan: And none of us pat cockroaches. You know, none of us go, 'What a nice little cockroach there.' 

Tegan Taylor: If I remember correctly, you brushed your teeth with a toothbrush that had a cockroach crawling over it.

Norman Swan: I did, I did, but it wasn't on the toothbrush at that moment. So there are common things that we will react to. Maybe I'm just unusual that filing nails is my area of disgust. I'm not sure what evolutionary protection that gives me, maybe having my eyes scratched out or something, I don't know.

Tegan Taylor: That's disgusting. So I guess to come back to the question, cutting mould off food versus chucking it out entirely, and the sort of risks associated with it, what should our rule of thumb be?

Norman Swan: Soft or hard? Although the compromise with bread would be can you get to a point where it's clean and you've got a reasonable margin between where it's mouldy, that's probably okay. But soft, essentially chuck it. And with hard foods, then you can cut the mould off.

Tegan Taylor: Good stuff. Well, I'm happy that my cheese is safe…ish. Thank you so much for answering these questions. Give Norman a round of applause.

Norman Swan: And Tegan.

Tegan Taylor: So we also answered some live questions at our live show.

Audience member: Going back to the penicillin and antibiotics, is it a rumour or is it true that if you go on them, particularly as a young child, you can feel worse after a week or two? You know, there's an understanding that it's not a good thing to give to children at a younger age, or if you're on them for a prolonged period of time, your health actually declines shortly after. 

Norman Swan: The whole thing about antibiotics is that you should only take them when you need them. And there are still a lot of people taking antibiotics when they've got a viral infection and they don't actually need them. So if you need them and a child needs them, then they should have them. What you're alluding to is that some antibiotics can change the microbiome. And there are some worrying long-term effects perhaps from antibiotic use. 

By the way, antibiotic use has also been associated with improved outcomes from cancer, and that's thought to be not the antibiotic but the infection. So infection seems to improve outcomes from cancer, and that's where they got the clue that the immune system might actually be able to be harnessed to fight cancer. So you wouldn't want an infection to run riot. It was more a sign that infection had triggered the immune system and helped to treat it. Now they've got drugs to do that. So the fact of the matter is some people might not feel that great after some antibiotics, which would be the microbiome, in which case you should be taking some natural yoghurt to replace the bugs that you've lost.

Tegan Taylor: Some keen beans in the middle over here at the back. 

Audience member: Thank you. So we were talking about the potential health effects of eating mould before, but one of the main places that I see mould in our house is actually in our coffee grounds, because they get mouldy really, really quickly when you, like, chuck them into a knock box. And so whenever we see the mould in there, we try to throw them in the bin, get rid of them as quickly as possible. But because we're not actually eating them, I tend to be a little bit less rigorous about it if I see it, I don't deal with it straight away sometimes because it's not full and I can't be bothered to throw it in the bin yet. Would there potentially be health risks associated with just having that hanging around in the kitchen in general? Or if you're not eating it and it's not particularly severe, is it not as much of a big deal? 

Norman Swan: Well, if your coffee grounds are anything like mine, they're damp, which implies that you're not really necessarily going to get the spores running around the room. But I must say, I'm pretty religious about getting rid of the coffee grounds. The bigger question with mould in the home is more mould in wood, mould in walls and so on, on that surface, and there is pretty good evidence that that kind of mould does cause respiratory disease, a risk of asthma, and perhaps some infections and so on. And there are some fungal infections…fungal infections are becoming a really, seriously problematic part of the health system. We're finding fungi that are resistant to anti-fungal agents and can devastate you when you're immune deficient. It's not the coffee ground problem, it can be environmental fungi, and when they're in a hospital environment it's a nightmare. But get rid of it. But I am comforted by the fact that when I fill my little stove-top up and put steam through it at high temperature, I'm assuming that I'm killing the spores, but maybe not.

Tegan Taylor: Thank you all for your questions. Thank you for coming along today and just thanks and well done everyone.

Norman Swan: So that's it for our live shows from the World Science Festival in Brisbane. We'll have our others linked in the show notes, on carnivore diet and cracking knuckles, and next year we'll have even more for you, but we'll let you know when we're out and live.

Tegan Taylor: And, as always, you can email us for live shows or not live shows, our address is the same, thatrash@abc.net.au.

Norman Swan: See you next week.

Tegan Taylor: See you then.