Spring is here!! After a long hard winter, I couldn’t be more excited about a little sunshine and warm days. Fueling the fire is DC’s annual cherry blossom madness. When spring hits, the CB’s come out and you can almost feel the excitement in the air. Here in the nation’s capital, we love our picturesque blooms. So in honor of the spring season, and the overabundance of marshmallow Peeps that flood the grocery store at this time of year, I thought I’d share a little seasonal food science and answer the question, “Why do marshmallows puff in the microwave?”
If you’ve never microwaved a marshmallow Peep, let me stop you right there. You’re missing out! Here’s three reasons why you should try it immediately:
1. It’s the closest thing you’ll get to a toasted marshmallow without a bonfire.
2. Even if you don’t care for Peeps, IT’S TOTALLY FUN TO WATCH.
3. Leftover Peeps become stale almost immediately, and this is a fun way to make them palatable again.
Here’s what you do:
Take a marshmallow Peep (or a regular marshmallow) and place it on a lightly greased or parchment-lined plate. Microwave it on high for no more than 45 seconds. Watch your marshmallow Peep puff and expand as it does its best Bruce Banner-meets-Jabba the Hutt impression!
Here’s the science behind what’s really happening:
Marshmallows are basically thousands of minuscule air bubbles surrounded by thin walls of gelatin and sugar syrup. When microwaved, the water molecules in that syrup begin to vibrate and heat up. They quickly turn to steam and fill the air pockets in the marshmallow, causing them to expand. This is why you see your Peep grow!
However, as steam escapes your Peep, the dehydrated sugar syrup left behind will heat up very quickly! You’ll notice that the inside of your Peep may turn brown. That’s because microwave heating tends to heat food from the inside. As the sugar exceeds 300F, it caramelizes (breaks down), creating brown pigments and a variety of dark flavors and nutty aromas. You’re likely also seeing some browning (even at lower temperatures) from the Maillard browning reaction, which requires both sugar and protein (in this case, from gelatin) to create brown colors and flavors. If you’re using vegan (agar or carageenen-based) marshmallows, you won’t get any Maillard browning.
Warming your marshmallow will cause the gelatin to melt, which will leave your peep structure-less once it’s pulled from the microwave. This means your Peep will collapse once all the steam has dissipated. Loss of steam also means a drier product–your marshmallow may pull and stretch more like taffy, and as it cools, it will develop some crunch. Just be careful as you’re eating, microwaved marshmallows can be very hot!
Most store-bought marshmallows are puffed by passing liquid marshmallow mixture through an extremely high pressure tube called an extruder. While under high pressure, gas is dissolved into the liquid without forming any bubbles. Then, when the marshmallow emerges from the tube into normal atmospheric pressure, the shock of the drop in pressure causes the dissolved gas to instantly expand and POOF–your marshmallow is “jet-puffed”.
Microwaved marshmallows are equal-opportunity. Kosher for Passover marshmallows can be obtained from your local store or online. One popular brand is Elyon, but they’re not the only brand available.
For those of you who want to get even nerdier with your Peeps, check out the website http://www.peepresearch.org. It’s a 90’s relic of a website dedicated to “Peep Research”. It was pioneered by a couple of scientists from Emory University with a good sense of humor and too much time on their hands. Lucky us! :)