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, 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.

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13 Responses to What’s the Science of Marshmallow?

  1. yasmin says:

    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. Henry says:

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

    • joepastry says:

      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. Cathy says:

    I made these Dark Chocolate marshmallows at Christmas to go with my ‘hot chocolate truffles’. Being dark chocolate and covered in cocoa powder, they don’t seem as sweet I think.

    Watch out though, cocoa gets everywhere when making these. /Cathy

  4. Another Joe says:


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

  5. sheree says:

    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!


    • joepastry says:

      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

  6. Heather says:

    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!

    • joepastry says:

      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

  7. katy kennedy says:

    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?


    • joepastry says:

      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

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