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When I first saw the following video - which is in Spanish - I wanted to share it with
my friends. Even those who don't speak Spanish. So, in collaboration with Arcadi Garcia, who
made the original, here is Gastrofisica in English.
Sugar - or, at least, refined sugar- is a white, odorless, fine-grained material, which
means that, in some ways, it behaves like a liquid. Caramel, on the other hand, is...
Uhhh... No. How does THIS turn into THIS? Well, it can’t be that complicated, right??
You heat up the sugar, the sugar melts, and then begins the process of caramelization,
which is a hot, sweet, sticky mess of crazy chemical shenanigans we’re not going to
get into; first because we’d have to get into too much chemistry, and second because
you know WHAT? This whole caramel thing isn't as simple as it looks.
First, we've got the chemical process of caramelization, which isn't very well understood. We know
that it's complex, that it creates HUNDREDS of different compounds and that it involves
LOADS of chemical reactions that, as I said, we’re not going to get into, and anyway
we don’t understand it anywhere near 100%. And don't get me started on melting sugar!
‘Cause I mean, in the first place, what temperature does sugar even melt at?
Different studies people have done on this don't agree. Some say this temperature. Some
say that temperature. In the end, it all seems to hang on whether to reach this or that temperature
you heat up the sugar fast or slow. Except the whole delightful concept of "melting point"
is precisely that, at the same pressure and so on, the temperature at which something
melts will always be the same, no matter how you got there!
The point of temperature is to give us an idea of how much kinetic energy the molecules
of a given substance have; how fast they move. In order to melt, the molecules in a solid
need, at the very least, a certain amount of energy to break free from their neighbors,
and that energy depends on the substance they belong to. Like, at atmospheric pressure,
water always melts at 0ºC, gallium at about 30ºC which is why it melts in your hand,
iron melts at around 1500ºC and sugar, apparently, WHENEVER THE HECK IT FEELS LIKE IT.
But if sugar - or, in other words, sucrose - melts, like, whenever it gets around to
melting, that’s because it doesn't actually melt: before getting to that point, it breaks
into its components: glucose and fructose. Glucose and fructose, which are more stable,
DO have real, proper melting points, and DO melt the way we think of when we think of
things melting, and they're what you see when sugar "melts" (you can't... you can't see
me, but I'm making some crazy air quotes over here).
Most recipes for making caramel talk about heating your oven up to 160ºC-180ºC [320°F
- 355°F]. And if you want to make it in a pot or whatever (like we’re doing in this
video), you can get things up to more or less that same temperature. But to simply break
sucrose into glucose and fructose, we don't need that much heat! That is, if we control
our excitement and instead keep the temperature around 150ºC [300°F] but for a longer time,
we can make caramel without having to melt anything: it just goes directly from solid
to solid!
To give this a shot, we tried to dry-caramelize some sugar cubes. With the oven set to 150ºC[300°F],
after 3 and a half hours look at these beauties! I mean, how sweet are these? Perfectly caramelized
sugar cubes without melting a single thing! They're sugar cubes, except, you know, caramel
sugar cubes. They taste like caramel, they smell like caramel, they ARE caramel. In the
form of a sugar cube. And yup, we were able to do all of this just because we tried to
understand the physics of caramel. Delicious, delicious, physics.