Making “Sun’mores” at 100ºF

Posted: June 25, 2025 | Author: | Filed under: Creations, Explorations, Food, How-to, That Totally Worked | Leave a comment

Yesterday the temperature in Boston, at Logan Airport out by the water, hit a new record of 102ºF (39ºC). The temperature outside my window in Somerville was 105ºF (41ºC), and I said “It’s so hot that you could make s’mores by just stacking the ingredients outdoors.” Ness said “you should try it! it seems like a you thing to do”, and they were right and I bet you can already see where this is going.

I stacked some chocolate and some marshmallows on graham crackers, arranged it all on a baking sheet, and put it outside on my porch deck. It was 3:46PM, and the sun was already well past its highest point, but the air itself was scorching and the chocolate started melting immediately.

I had to move the tray from the front of the house to the back to keep it in direct sunlight. At the same time, I decided to try an experiment: putting a glass ‘greenhouse’ dome over some of the marshmallows to see if it helped them melt. For that I used pint glasses, which coincidentally (I presume) are almost exactly the right size for a standard graham cracker.

Now things were really heating up. The air temperature was 104ºF (41ºC), but the chocolate’s dark surface had allowed it to absorb more of the sun’s energy, and I measured its temperature as 159ºF (71ºC)!

In addition to the traditional graham+chocolate+marshmallow combination, Molly set up a fruit combination: graham+chocolate+raspberries, which you can also see in the first photo above.

The ingredients had now been outside for just exactly one hour, the sun was starting to get lower in the sky, and even though I was only running outside for quick checks on the ingredients, I was getting overheated and it was time to move on.

Time to assemble the final product! But: would the chocolate really be entirely melty? Would the marshmallows really be gooey all the way through? And would the greenhouses have made any difference? It was time to find out.

Although the marshmallows hadn’t deformed just sitting there, they were really quite gooey, and the greenhoused marshmallows were, in fact, even softer and gooier! Assembling the final sandwiches was easy, and everything melted and mixed and blended, just like campfire s‘mores.

I bought the (very hot!) baking sheet indoors, where Molly, Sarah, I, and a couple of area teens did some long-awaited taste-testing. It worked! We had tested my hypothesis that you could make s’mores just by putting the ingredients outdoors on a 100ºF day, and found that you can, and should! If we had started closer to solar noon, and if we’d put a greenhouse over all the ingredients (perhaps a glass 9×13 baking pan, upside down?) I think they would have gone much faster, perhaps in 20-30 minutes.

The fruit combination, raspberry+chocolate+graham was particularly delicious, and felt extra summery. Molly suggested next time doing fruit+cheese, and Sarah joined in to say that if we did that next time, that we should put it on something better than a graham cracker.

After some back and forth, we officially named these “sun‘mores“, and decreed that they can only truly be created on days when the temperature hits 100ºF, which it certainly did yesterday!

And when Ness saw all this they exclaimed simply, ”by jove!!!”