I always love a science project that also creates a tasty treat, and this one is also functional. Have you ever wondered: Is my oven too hot? Or, how do I calibrate my oven? Or maybe you just get frustrated and ask yourself, why won't my cookies bake right? Well, we might have some answers for you, because I hate burned cookies just as much as you do (well, likely, some people actually like burned cookies).
If you think you are baking at 350, but really your cookies are roasting at 360, you will find that you are continually burning your cookies. Likewise, if your oven runs cold and your oven is really trying to cook the cookies at 340, your times will always be off - so how can you fix your oven temperature? You can calibrate your oven! This is fun, tasty, and gives you a chance to talk about not only the science that is involved in cooking but also the states of matter and phase transitions!
To calibrate your oven with sugar you need nothing more than an oven (that seems obvious), a metal baking pan lined with foil (don't skip the foil), and sugar.
Preheat your oven to 350 degrees and scoop 1/2 tablespoon mounds of sugar onto the baking sheet in the same way you would scoop cookies out. Put your pan in the oven and wait 15 minutes. If you find the sugar is melted, your oven runs hot (sugar should melt at 366 degrees). If nothing has happened, turn your oven up to 360 degrees and wait another 15 minutes to check. If your sugar hasn't melted, bump up the temperature by another ten degrees, check after 15 minutes. If the sugar isn't melted after 15 minutes at 370 degrees then your oven runs cold, but keep going on this route until your sugar melts so you know how cold your oven runs.
Once you have little piles of melted sugar take the pan out and let it cool for 10 minutes. Peel the sugar circles from the foil and eat!
Our oven runs a bit hot, these started melting at 350. What is also neat to see is the hot spots in your oven. From the picture below I know that the cookies on the outside of the pan will likely burn, while the inside cookies won't quite be done yet.
We waited a little longer for everything to melt (which caused the outside sugar to burn) before removing it from the oven. After they cooled they can be peeled right off for snacking. This was fun for us since I was always burning my cookies, and likely because our oven runs really hot, about 15-20 degrees hot in some places!
Unlike how ice melts into water and can be refrozen again, sugar doesn't melt. Sugar decomposes into a liquid based on temperature, but not all temperatures are equal. If you heat your sugar high and fast, it will liquefy at a higher temperature than if you heat it up at low temp slowly.
For an object to 'melt', it has to have the same chemical composition before and after it melts. Ice is H2O in a crystalline structure. It melts into H2O in a liquid structure. H2O is H2O, it is the same chemical compound, just in different states (solid and liquid). Even if we heat the liquid to steam it is still H2O (but now a gas). Sugar, however, is not the same before and after.
As sugar heats up the molecules begin shaking around faster and faster. When they move fast enough the bonds holding the sugar molecules into the crystal structure break, causing the sugar to apparently melt. But these sugar molecules keep on shaking around, faster and faster, more and more, until they rip themselves apart. That's right, the sugar molecules shake so much as they heat up they not only tear apart the crystal structure, but they tear themselves apart! Now when the sugar cools it is a bunch of little broken up pieces in a glassy structure instead of actual sugar! Imagine wood melting. You can't because wood doesn't melt like water does. Neither does cardboard, or thread, or sugar.
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