What’s the Science of Marshmallow?

That’s a good question, reader Jay. Marshmallow is one of the simpler foams, but still an interesting object to contemplate. It’s primarily a sugar syrup with lots of air whipped into it, though it wouldn’t hold up for terribly long if it didn’t have some sort of support. That support is usually gelatin.

I’ve discussed gelatin exhaustively in the past. The shorthand is that it’s made of long-chain protein molecules which in their natural state are chemically bondered together and coiled around each other like rope. When heated in liquid, geltain proteins release their bonds, uncoil and disperse. As they cool they start to bond to one another again. However having uncoiled they can’t go back to their original, tight configuation. The result is a loose network of interconnected molecules that prevents other molecules around them from flowing. A semi-solid material results.

So imagine if you will a thick sugar syrup in a mixer. As the whip goes around thousands upon thousands of tiny bubbles are introduced. The mixture becomes thicker, but not thick enough. That’s where those gelatin proteins come in. They surround the little bubbles, reinforcing them and preventing them from popping. As the marshmallow cools the gelatin proteins bond to each other, effectively freezing the whole matrix in place.

Oh, and to answer your question, reader Mari, the reason the semi-clear liquid turns into a bright white material is because of all those teeny tiny bubbles. They prevent light rays from passing through the mixture, and bounce them right back to our eyes.

19 thoughts on “What’s the Science of Marshmallow?”

  1. question. i don’t eat most things with gelatin in them because it’s usually pork-derived and i’m muslim. i currently have a packet of agar agar at home. do you think it would work sufficiently for marshmallows? or would it be too weak and not worth a shot?

  2. Hi Joe, is it possible to make marshmallows that are not so sickeningly sweet? Since it relies on gelatine for setting anyway…

    1. Hey Henry!

      I can think of alternatives for the gelatin, but not for the sugar. Marshmallows are technically a candy. I can’t think of anything offhand that will behave like sugar syrup when it’s whipped. Hm. Anyone out there have an ideas?

      – Joe

  3. Yasmin,

    You can get kosher gelatin extracted from fish bones and they do a great job with marshmallows.

  4. Hi Joe!

    I tried making marshmallows yesterday subbing Bailey’s for water. I’ve made marshmallows with other liqueurs before, and was successful, but for some reason, the two batches I attempted to make failed to form, or didn’t form enough air bubbles during the whipping process. I feared it may have been my mixer, but I made a regular batch of marshmallows today just fine. Any ideas what might have happened?

    Thanks for your help!


    1. Hey Sheree!

      I’m not precisely sure, but I think may have been the milk fat that’s in Bailey’s that caused the problem. Fat is hard on foams just generally. You may want to try whipping up the mixture, then adding the Bailey’s once the foam is whipped up…that works for egg foam recipes like soufflées and buttercreams. Whether it will work for Bailey’s marshmallows I’m really not sure. Good luck!

      – Joe

  5. Hi there,
    my 8 year old and I are doing a science fair project on the science behind marshmallows, and we have a question that we have not found anywhere else – why does gelatin smell so much worse when heated as opposed to room temperature?
    Any insight on this would be great, thanks!

    1. Hey Heather!

      I get similar questions a lot, for recipes that involve hot water and gelatin. People throw it away because they’re convinced it’s spoiled, but of course dry gelatin really can’t spoil.

      The reason gelatin stinks is because it’s made from long boiled pork (or beef) skins. The gelatin (a type of protein) in the skins melts into the water and is later separated out, refined and dried to make gelatin powder and gelatin sheets. All that refining however doesn’t produce perfectly pure gelatin. It still has a very small amount of miscellaneous porky impurities in it.

      Normally we don’t notice those because gelatin is frequently mixed with cold water then melted in warm water. Occasionally however it’s mixed with hot, steaming water, and it’s that rising steam that picks up those impurities (aromatic oils and such) and delivers them to our noses. The result is a whiff of the barnyard. Call it the pig’s revenge. Sometimes it’s enough to put you off your marshmallows…at least until the mixture cools down and the smell goes away.

      Hope this helps!

      – Joe

  6. Hi Joe

    I have made marshmallows a few times and they are always yummy but have never been as big as the first time I made them (despite using the same recipe). I also checked out some other recipes and some call for boiling the sugar to the soft ball stage and some to the hard ball stage. Equally others call for ice cold water for the gelatine, others for you to heat the gelatine.

    Can you tell me the reason for using hot or cold water in the gelatine and which temperature to heat the sugar to and why please?


    1. Hey Katy!

      Good questions. As far as gelatin is concerned, cold water is best for dissolving and hydrating it. Once that’s done you want to apply hot water to melt it. Make sense?

      Regarding the syrups, I’m fine with a soft ball syrup, though you’ll get a higher whip with a hard ball syrup since it has less water in it. You marshmallows will be firmer, but if you don’t mind that you’re good!


      – Joe

  7. Hi Joe
    I would like my marshmallows to last for as long as possible (if I can resist eating them all!), but I notice the texture starts to get grainy after a number of weeks. I read that the dextrose value of the liquid glucose I use may make a difference? Also, when I make chocolate marshmallows they grow mould after a few weeks.
    Would really appreciate your advice.

    1. Hi Phil!

      Very interesting. The crystallization problem would be better helped by introducing some longer-chain starches into the mix, which will get between the smaller simple sugars as they try to form crystals. Can you lay your hands on some nice thick corn syrup? As far as the mold, drier storage is they key there. The sugar is absorbing moisture from the air and creating little drops of syrup that are just dilute enough for mold to grow on. Are you dusting your marshmallows well with confectioner’s sugar? It usually contains a little bit of corn flour as an anti-clumping agent, and that helps keep the surface sugars dry.

      Best of luck!

      – Joe

  8. Firstly, Thank you for this post! I am constantly searching to understand the fundamentals of how ingredients work and their necessity towards a certain recipe, and now I know the importance of gelatin.
    I’ve been experimenting with raspberry marshmallows, made with fresh raspberries pureed and strained, but am not happy with the flavor outcome of both eggwhite recipes and egg–free recipes.Do you have any experience or thoughts to share on this addition?
    P.S. I dissolve the gelatin in a separate bowl, then after pouring the sugar/syrup into the mixer to be beaten, I put the gelatin into the still hot pan and use the resonant heat to melt it 🙂

    1. Hey Nissa!

      Very interesting. If I may ask: what is it that you don’t like about marshmallows with egg whites?

      – Joe

  9. Hi Joe,

    I have started to experiment with different recipes. However, I find that from batch to batch the consistency of the marshmallows changes. Sometimes they are super fluffy and awesome, sometimes they just never really solidify and retain too much of a watery state. This comes to be a problem especially when we try to heat them up like a s’more or anything, they just melt away. I have read that even a slight change in temperature can do this (I use an analogue thermometer so I may be off a couple degrees from batch to batch) could that be the problem? Or is there a way to make them a bit firmer in general to allow for roasting? LASTLY (I promise :P) I live in Denver, does altitude change a lot? I read something about I need to count my altitude into my temp readings with an analogue thermometer? Would that be the same case if I just got a digital? Sorry for all the questions, the first batch was so awesome and I loved it, now I can’t get back to that!

    1. Hey Justin!

      I’m so sorry for the late reply, but I’ve had a deluge of very technical questions lately and have been typing my fingers off!

      My feeling is that yes, you need a more accurate thermometer. That could very easily be the source of the problem you’re having, since even very small amounts of moisture can turn sugar into a syrup — and your syrup’s temperature, in addition to being a measure of how hot the syrup is, is also a measure of the syrup’s moisture content. So if, for example, your thermometer is a few degrees off, you could have enough extra water in the syrup to ruin your texture.

      The good news is that digital thermometers are very cheap these days and are extremely easy to use! Get one and get back to me if you’re still having problems. I promise I won’t take so long next time!


      – Joe

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