In which I confront a domestic mystery

Some late nights in the lab, that vending machine chocolate bar just can’t fill the snack hole that only a truly grueling experiment can induce. You need something hot, salty and preferably dripping with fat.

It’s no surprise, then, that microwave popcorn is the scientist’s best friend. It ticks all the boxes: flat-pack construction for easy storage, non-perishable at room temp, cooks in only five minutes and – unlike sweets – doesn’t hit your stomach too hard when it’s running on empty. During graduate school, microwave popcorn undoubtedly kept me from certain starvation. Its only downside, as far as I can see, is its tendency to radiate a mouth-watering aroma all over the institute in a matter of seconds such that, by the time it’s finished popping, you might have acquired a few hopeful onlookers (typically malnourished PhD students). I find that an apologetic smile and a “Sorry, I haven’t eaten for twelve hours and this is my dinner” is enough to disband the hyenas.

I’ve been popping microwave corn for about 25 years now, probably on hundreds of different machines. I’ve popped them in cheap set-ups in the common rooms of university accommodations, in Soviet era contraptions passed from student to student in group houses, in all the various flats I’ve lived and institutes where I’ve worked in several countries. And I’ve tried all the major brands of corn. Despite the wide variation of conditions, the general recipe has remained surprisingly constant: put the bag inside, set the microwave on ‘high’ for five minutes, and press ‘start’. Sometimes between about 3.5 to 5 minutes, depending on the machine, the pops will slow to about a second apart, and then you know you’ve reached the point of diminishing returns: all of the kernels haven’t popped, but if you leave it longer, the popped corn will start to dry out and scorch. Usually you’re left with about 20 to 30 unpopped kernels after an average session.

When we moved into my new house last year, we ordered a very swanky Panasonic microwave/oven combo from John Lewis. It was easily the nicest and most expensive microwave I’ve ever had access to. We’d had it a few days and I’d used it for a few basic operations – reheating coffee, defrosting meat and the like. Nothing fancy, but everything seemed to work fine.

And then, I tried to pop some corn. The corn didn’t even start popping until after 4 minutes, and after the bell dinged at 5, only about a quarter of the kernels had popped. The bag was very hot, though. Perplexed, I put the bag back in for another 5 minutes and ended up with about 50% yield. I wrote it off as a fluke, but a few days later, I chose a bag from a new box and set the timer for ten minutes. The dynamics were similar, as was the result. The corn was a brand I’d been using for the past few years on two very different microwaves, so I knew it wasn’t likely to be the product. But the oven seemed otherwise fine, and I’d feel ridiculous taking it back for an exchange on the basis of “suboptimal popcorn performance” – the complaint was just too niche. So in true British fashion I decided to live with it.

And then one day, a few months later, I produced a perfect bag of corn after five minutes.

What had changed? I remembered that a few minutes before I’d made the corn, I’d heated up some hot water in a mug for a minute or two. Could it be that the microwave somehow had to be pre-heated or primed for optimal corn performance?

Dear reader, I did the experiment the following evening. And it seemed to work: half a mug of water for two minutes on high was enough to prime the oven to pop a bag of corn to about 80-90% of its usual yield after about 6 minutes. Not perfect, but definitely getting there.

The funny thing is, it doesn’t always work, and it fails more often than it succeeds. I think there are two important variables: exactly how much water you have in the mug, and how long after the mug run finishes before you introduce the bag of popcorn. My downfall up until now has been improper documentation, so these impressions are only anecdotal. But from now on, I’m determined to do things scientifically: to use the same mug and systematically vary amounts of water heated for the exact same amount of time; and to systematically vary the time between mug heating and bag introduction. I already know that straightaway is too quick, and five minutes is too long. So I’m hopeful to have the formula nailed over the next month or so.

In the meantime, if anyone out there can diagnose what’s wrong with my addled Panasonic based on the meager data to hand, I’d love to hear all of your theories.

About Jennifer Rohn

Scientist, novelist, rock chick
This entry was posted in Domestic bliss, Nostalgia, Scientific method, Silliness. Bookmark the permalink.

52 Responses to In which I confront a domestic mystery

  1. Cath@VWXYNot? says:

    We’re going to need graphs and a detailed statistical analysis.

    Good luck!

  2. NatC says:

    You pre-heat the microwave with a mug of water? Does it work if you pre-heat anything else?
    Could popping-efficiency somehow vary with humidity?

  3. Oh, that’s an interesting thought. I should mention I tried it with an *empty* mug and it didn’t work. But I ought to whack in a chunk of frozen meat – something with the same mass as the water but not as…er…wet.

  4. That’s funny! I did the same thing several years ago when I had to replace a microwave with an older model that my sister gave to me. When I popped a bag of popcorn, only about 1/2 of the kernels would indeed pop. It was quite frustrating. And then when I had some friends over, I decided that I’d need two bags. And after taking out the first “popped” bag, I immediately put in the second bag. And to my surprise, the whole bag (well, for the most part) had popped!

    And so I started microwaving a mug of water to “prime” the microwave, which seemed to get me pretty close to a full bag.

    It’d be interesting to find out if there is an explanation.

    I totally forgot about this – it plagued me for about six months, before I got a new microwave as a gift.

  5. Wow, what a coincidence! It makes me feel slightly less as if I’m going mad, which is a good thing.

  6. Steve Caplan says:


    Just be careful not to eat too much microwave popcorn– you don’t want to get “popcorn lung”

    Seriously, I see the same thing when heating up 2 bowls of soup serially. If the first takes 2.5 min. to heat and boil, the second one might take 30 sec. less. A good experiment would be to see how long an interval is needed so that the “priming” doesn’t work. Mechanistically, though, reviewers want to know how the priming occurs at a molecular level!

  7. ricardipus says:

    Hm… does this oven by any chance have some kind of clever temperature sensor inside it? Is it perhaps that the air inside it is warmer once something else has been heated?

    I am grasping at straws here, obviously. Also, you’ve made me hungry – good thing it’s supper time over this side of the pond. 😉

  8. Interesting dilemma, I too am a microwave popcorn aficionado and have been suffering dearly as our flat did not come with a microwave (nor is there space for one…but we’re moving house soon!).

    Another variable to consider is the temperature of the water prior to being placed in the microwave. If it is a humidity related effect, then water temp is important.

    First thought that comes to mind: perhaps for some reason there is less heat transfer from the walls/bottom of the microwave to the bag in the new microwave versus older models. Increasing the humidity increases overall transfer of energy from microwaves to the bag via the additional vaporized and/or condensed water molecules. Would probably be more important for something that has less water content than most foods heated in a microwave. You could check the temp of the walls in the new microwave versus older models. Could also use a spray bottle to wet the outside of the popcorn bag…

  9. Chris says:

    Wow. This is the best snack idea ever. It has never occurred to me… just wow.

    My first thought was also that it is probably a humidity related effect. Could just measure humidity in microwave before and after priming with water and in new vs old models? Although I’m not sure how easy you can get access to a hygrometer …

  10. Steve Caplan says:

    Intrigued, I related the story to my 9 y old son, who loves anything to do with physics (and popcorn). His explanation: the heated water evaporates and the remaining steam in the microwave conducts the heat better than the air. I think NatC, above, had the same general idea…

  11. Intriguing, testable hypotheses…keep ’em coming, folks. I’m a little skeptical that humidity could *enable* a process that drastically, and make the difference between 50% popped after 10 minutes vs 90% after 3.5 minutes. Humidity may help, but surely there is some intrinsic problem with the machine that the humidity is “rescuing”, which I’d also like to understand. I definitely need to heat up a solid, relatively non-wet mass and see what happens, although I can’t rule out, without the hygrometer, that this releases enough moisture to substitute for the lack of a hot mug of water. Anecdotally, I’ve seen no difference in popping efficiency in microwaves based in Seattle and DC (relative high humidity) and in Colorado and New Mexico (relative humidity practically non-existent). 🙂

  12. Also wondering – wouldn’t a build-up of heated air or humidity mostly disperse when the door was opened? It makes me lean towards an idea that the materials inside the oven might be what’s storing up the energy that makes the corn pop more efficiently.

    I toyed with the idea that it was the oven/microwave combo that was causing the problem, but I’ve owned several combo machines and have never had this problem.

  13. Rivka says:

    Jenny, when I was in Indiana I bought popping corn that was still on the cobs – it actually said on the instructions to boil a cup of water beforehand in the microwave. It worked very well but did not stay in the bag and when we opened the door cascades of popcorn festooned the kitchen like the magic porridge pot. Think there is photographic evidence somewhere xxx

  14. Just to say that anyone who is seriously impecunious or doesn’t like the additives you get with the packs of microwave popcorn, you can buy popping corn in health food store, shove a little bit into a large microwaveable dish with lid (preferably transparent to monitor progress) – add tiny bit of oil and salt, and cook on full power; I find in my microwave it usually is done in around 3-4 mins.
    I have no idea about why you are getting odd results with the Panasonic. I applaud the scientific spirit of enquiry, but I’d be inclined to complain to Panasonic – it still seems possible that you have an erratically dodgy microwave.

  15. Eva says:

    If it’s the humidity, rather than “priming”, you can probably test this by putting a small cup of water in *with* the popcorn. Does that make it go faster?

  16. Eva says:

    Also, I only just found non-microwavable popcorn here in the UK, so I can finally enjoy popcorn again! (Don’t have a microwave…)

  17. cromercrox says:

    Jenny – you and your commentators are missing the obvious solution. The microwave retains a memory of the water.

  18. KristiV says:

    I think cromercrox has solved the mystery! 😀

    There are inexpensive containers purpose-made for popping popcorn in the microwave, without adding oil; I bought one (I know, I know, yet another kitchen gadget to store) because I have relatives who grow popcorn, and I always have a jar of the stuff in the pantry. I also like adding various seasoning mixes from Penzey’s. But for long days at work, I keep the flatpack pre-seasoned variety on hand, and there’s significant variation in the popping completeness and tendency to burn between different microwaves around the department. For example, the microwave in my lab almost always burns a hole through the bottom of the paper flatpack, without burning the popcorn itself.

    In graduate school, a few of us used to get together frequently and make different kinds of popcorn for dinner. We usually popped it using the old-fashioned stovetop method (no microwave), and then added grated cheddar (Tillamook) or Parmesan cheese for protein. Much better than other cheap grad school food options, like ramen noodles.

  19. I adore Tillamook cheddar – what a fabulous idea.
    I’m not adverse to popping stuff on the stove, but it does dirty the only heavy-duty frying pan we have, which is sort of a pain when it comes time to make supper. I will definitely look into these mysterious containers! And would absolutely love to reproduce Rivka’s on-cob experience!

  20. It surely is the water – since it is the expansion of water (native or otherwise) that makes the popcorn pop. Your variability is presumably due not only to how much water in the mug, but how long you left the door open to let the moisture escape in between. You need to do more experiments with this too, deliberately dispelling the moisture you create, to check it out. (And yes, along with onions and carrots I’ve worked on cheesy wotsits, though not popcorn)

  21. Athene, why isn’t the native moisture in my popcorn enough for adequate performance in the absence of the hypothesized humidity priming? Just curious what you think.

  22. Try leaving it near a steaming kettle first to see if that helps. Maybe (since water is relatively heavy) they’re now selling it drier to reduce transportation costs?

  23. Heather says:

    Ack, Athene got there first. You hear it then from an independent source.

    Perhaps your Panasonic is better ventilated than your older models? Or vice-versa?

    I’m also capable of eating an entire bag of popcorn – and you’ve inspired me to get one out RIGHT NOW, although it’s not part of French lab culture in the slightest – but I am absolutely convinced that it was popcorn hulls that accumulated in my appendix and caused two bouts of sub-acute appendicitis before it eventually ruptured a decade ago (when I was a not-quite-starving postdoc). Now I figure I have nothing left to lose, since I survived that experiment.

  24. Heather says:

    DAMN. I am out of bags. Anyone want to send one over?

  25. Sorry guys, not to have been clear – the corn works on another microwave. It’s not the product.
    And multiple products don’t work on my microwave.

  26. Frank says:

    Jenny –

    Have you done a literature search yet? A quick-and-dirty search in Scopus suggests that you have identified an under-researched topic, which is to say that I couldn´t find anything on the precise question you asked. But, in best Librarian fashion, here are some tangentially-related articles that may (hoping against hope) lead you a little closer to the answer.

    Role of the Pericarp Cellulose Matrix as a Moisture Barrier in Microwaveable Popcorn
    Biomacromolecules, 2005, 6 (3), pp 1654–1660

    The effects of ingredients on popcorn popping characteristics
    International Journal of Food Science & Technology, 2004, 39(4) pp 361–370

    Effects of bag capacity, storage time and temperature, and salt on the expansion volume of microwave popcorn
    Journal of the Science of Food and Agriculture, 2001, 81(1), pp 121-125;2-E/abstract

  27. Hmm, now that’s interesting. The phrase “Role of the Pericarp Cellulose Matrix as a Moisture Barrier in Microwaveable Popcorn” suggests that moisture is a BAD thing for microwave corn. Does that shoot our humidity hypothesis in the foot?

    Meanwhile, a twinge of nostalgia for the third example – I used to preside over that particular journal. It was full of weird and wonderful topics but I think my all-time favorite was a study about optimal chapati flour to maximize curry scooping potential.

  28. PaoloV says:

    Hi Jenny,

    I’ve been thinking about this after you mentioned it at PubSci last night.

    Have you checked the power of the extraction unit? If this is a high spec microwave/oven it may have more powerful extraction than the microwaves you’ve used in the past, which may act to reduce the humidity within the cooking area. If so, it may be that there are insufficient water molecules in the air of the cooking compartment to allow the ambient temperature within the microwave to get high enough to facilitate efficient popping (or perhaps to allow transfer of heat within the popcorn – same outcome).

    Microwaving a mug of water beforehand should increase the humidity inside the machine to the point that the air is more saturated and therefore heats up due to the action of the microwaves. If this is the case, it may be that your variable results are caused by fluctuations in environmental relative humidity.

    Obviously the humidity inside the bag of popcorn should be the main factor, given how a microwave works, but I have no idea of the permeability of a popcorn bag to atmospheric moisture.

  29. ricardipus says:

    Charcoal for barbeque-ing.

    Proper kettle-boiled water for tea.

    Hot air for popcorn popping.

    I’m just sayin’.

    Also – does your microwave have a “popcorn” preset button? Have you tried that?

    *runs away

  30. rpg says:

    I’ve promised to buy Jenny a hot air popper, just to stop her worrying about this…

    And no, it doesn’t have a popcorn button.

  31. You’re right; hot-air poppers never strike me as being particularly moist environments…still not sure I buy the humidity theory unless it’s that greater humidity allows for a hotter overall temperature inside the oven (much as a wet autoclave is REALLY BLOODY HOT).

  32. Just had an image of trying to pop microwave popcorn in the autoclave…not sure the kitchen staff would approve! Although the kitchen staff at my PhD Microbiology department used to make the annual Christmas pudding in the autoclave…consumed with equal parts gusto and trepidation, it has to be said.

  33. rpg says:

    *laugh* Actually, that rings a bell–someone else told be about Christmas pudding in the autoclave. It’d be sterile, there is that.

    Anyway, I’ve had a quick google and there’s an experiment I’d like to try with the popcorn.

  34. Steve Caplan says:

    There we are, caught on type– typical chauvinistic attitude: “I’ll buy it for the lady”…

    *retreats to the shadows*

  35. rpg says:

    If you were a gentleman, I’d meet you in the car park in five minutes.

  36. Steve Caplan says:

    I’m here in the carpark, Blackberry unsheathed…

  37. rpg says:

    ‘Blackberry’? *snigger*

  38. Steve Caplan says:

    Headline: Underdog Blackberry deals Goliath Iphone stunning blow

  39. rpg says:

    You couldn’t stun your way out of a class A subnet.

  40. Steve Caplan says:

    Actually, since class A subnets have 254 unique network addresses, and therefore about 17 million unique nodes, I would use masks beginning with with the last 3 octets to address hosts on a LAN…

  41. rpg says:

    You are indeed in a maze of twisty nodes, all alike.

  42. ricardipus says:

    Are you back? I thought you and Steve were in limbo somewhere.

    Somebody (not me) once re-labeled the “popcorn”, “soup”, etc. buttons on a lab microwave where I worked as “blot wash”, “agarose gel”, and “mouse”.

    This same person (not me) once also got the dilution of ethidium bromide wrong by a factor of 1,000, ending up with litres and litres and litres of the stuff.

    He’s now an MD.

  43. rpg says:

    “Where he can no longer do any harm”?

  44. Steve Caplan says:

    What’s a few thousand-fold among friends–or patients?

  45. cromercrox says:

    The mention of autoclaves reminds me of a a true story told me by a fellow student when we were undergraduates – of nursing students caught sniggering round a textbook which declared, in all seriousness, that nothing should ever be placed in the human vagina unless it had first been autoclaved to 150 degrees Centigrade.

  46. vrk says:

    Microwave ovens use klystrons to generate the microwave radiation (incidentally a similar unit is used in radars), and klystrons can only operate in two modes: on or off. If the oven is rated at, say, 800 watts, and you select, say, 600 watt operating power, it means the klystron will be switched on 6/8 = 3/4 of the time and off 2/8 = 1/4 of the time, to get an average output of 600 watts.

    However, microwave ovens differ in how they accomplish this. The most naive algorithm is to turn the klystron on for 6/8 of the programmed time (in this example), then turn it off and let the heat diffuse through the food. More expensive models have very varied power profiles, especially if you use the preprogrammed defrosting options (“defrost 250 grams of peas” or something).

    This doesn’t directly explain why heating water first works, but it could be that the CPU (yes, these things are computers nowadays) decides, on reading the internal temperature sensor, that a different kind of a program is needed compared to an empty and cold oven. So even if you select maximum output power, the oven might decide to run the klystron only part of the time to balance things out.

    I’m not a microwave engineer, but this is not the first time my military training could be of use…

  47. Wow, what an amazing explanation. Thank you. So this is sort of the equivalent of an automatic car – the car decides when to shift the gears, even when you as a driver are gritting your teeth because you really would have gone over the 3rd gear ten seconds beforehand and have to listen to the engine struggle.

    But maybe there is a hope here: I could try to pop corn using one of the pre-sets, which might just by chance have a more favorable on/off pattern…hmmm. What is popcorn most like, on the molecular level? Pizza? Casserole? Cold pasta?

  48. rpg says:

    I can see us eating a lot of popcorn this weekend…

  49. I haven’t gone off to read the Biomacromols paper (sorry to be lazy, but it’s late, although it is a journal I often read), but the title may actually refer to the pericarp as stopping the popcorn getting ‘stale’ and ‘soggy’ before it ever gets into the microwave, thereby changing the starting material rather than the microwaving process per se.

  50. Tideliar says:


    *day late, dollar short*


  51. daedalus2u says:

    You want to heat the popcorn at the highest power setting.

    Popcorn popping is a nucleation phenomenon. The water in the kernel becomes superheated (heated above its normal boiling point) and then nucleates into steam explosively.

    Many microwave ovens do not have a uniform microwave distribution and the heating of water depends on where the standing waves of the microwaves are located. When heating something large and fluid, such as a mug of water, the non-uniformity doesn’t matter that much. In heating something like popcorn, it does.

    Popcorn pops when it reaches a certain temperature above the boiling point and then nucleates. The kernels are heated according to their location in the standing waves of the microwave field, but they can cool by conduction to other surfaces or to kernels that are not being heated. Kernels can also shield other kernels from microwaves and also from losing heat too rapidly. Agitation can also trigger nucleation. It is possible to get explosive nucleation where the popping of some kernels triggers the popping of others in a chain reaction.

    You want the highest power setting, and you also want the package of popcorn located in the right location.

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