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Originally Posted by shakran
If nothing else the flame will caramelize any sugars in the food. That's why a creme brule's sugar coating (you caramelize it with a kitchen torch (not mapp gas as I discovered once  ) ) tastes very different than if you just sprinkled the sugar on top and left it as is. |
I don't think this is right--again, to use the trash analogy, blowtorching the top of a creme brulee is like blowtorching the contents of a trash can directly--instead of an empty trash can, you'll end up with a pile of ash.
Broiling or blowtorching a creme brulee heats up the sugar past its melting point (146 C, or 300 F) and to the point where caramelizing reactions occur (I don't know what temp this is). The suger isn't combusting--it's just being heated up, liquifying, undergoing some kind of caramel (non-combusting) reaction, and then recrystallizing. All of this is possible to do without a flame--candy factories don't need actual fire to make caramel or hard candies.
The flame in creme brulee is heating up the creme brulee itself. Or, more specifically, just the top of it, while the delicate custard below stays intact. That the end of a blowtorch is flaming is not important--what's important is that the end of the blowtorch is very very hot! This allows you to heat up the surface to the necessary temperatures without subjecting the custard below to the heat. In contrast, the flame from a sauce with alcohol should have little heating effect on the food itself. It's the mix of alcohol vapor and oxygen that makes the reaction possible--the flame occurs *above* the food, not on it, and since heat rises, I doubt that it heats up your food more than what your frying pan can produce on its own (after all, if you have a gas range, your frying pan is already sitting on top of a flame). Moreover, the flame is short-lived--I've never had one from a sauce last longer than 10 seconds. When making a creme brulee, you can spend a minute with a blowtorch to get the right reaction!