How does a deep fat fryer carbonize things if they aren't being burned? Or, how can they be burned if not exposed to oxygen?

January 22, 2004 9:34 AM

When something burns it uses up it's fuel/calorific content and turns into a small blob of black which is known to chemists as 'carbon' and to the rest of us as 'bugger'. This I can cope with.

If you stick the same item (or an unburnt relative of said product) into a deep fat frier and heat it for too long, it goes black and creates this same black substance. There has been no oxygen for the the energy to burn with. Where did the energy go?
posted by twine42 to Science & Nature (10 answers total)

does it really? i mean - have you tried it, and made sure it stays at the bottom of the oil and doesn't float around on the surface?

it would be interesting to burn/heat in oil two identical samples and compare their weight afterwards. but i don't know how you'd remove the oil from the cooked sample.

incidentally, i don't know what you mean by "where did the energy go?" the problem seems to be "where did the oxygen come from?". if the heated sample is burning, the energy would simply go into raising the oil temperature a little. if you're asking where the flame is - well, the flame needn't happen for the reaction to occur.

my best guess without doing the experiemnt and seeing what it looks like is that in the oil case you're not generating carbon by burning (ie combining oxygen from the air with hydrogen in the organic fuel to leave carbon), but rather breaking down/reforming the chemicals present into some kind of organic gook.

alternatively, maybe there's some oxygen bound to the oil that can be used to "burn" the sample, and the oxygen-less oil is then either "spoilt" or recovers on the surface.
posted by andrew cooke at 9:58 AM on January 22, 2004

oops - description of burning is a little off. some carbon is also lost as carbon dioxie/monoxide.
posted by andrew cooke at 9:59 AM on January 22, 2004

I'm not sure, but I do know that when you dump something into oil, you'll likely notice lots of bubbling. That's usually water content in the item dropped into the oil being converted to steam by the high temperatures. Lots of Oxygen in those bubbles I'd imagine, and plenty more in most porous objects as well.
posted by willnot at 10:18 AM on January 22, 2004

It's still there--the black substance you get from deep-frying it is, in fact, not the same black substance you get from burning it.

If you've ever burned a log in a fireplace, you know that it leaves an amazingly small amount of ash, compared to the size of the original log. Most of the mass of the log escapes as gases.

If you deep-fry a log--even if you let it go long enough so that the entire thing comes to the temperature of the oil--it might turn black, but much of the log will still be there. (The water will boil off, if it can escape from the log, but you'll still be left with much much more--and probably in a single piece, I'd guess--than you got from burning the log.)

Now, if you do this with a carrot, for example, the burned carrot and the fried carrot might well look much more alike than the burned log and the fried log did. But that doesn't mean that the burned carrot and the fried carrot are actually the same substance.
posted by DevilsAdvocate at 10:23 AM on January 22, 2004

Lots of Oxygen in those bubbles I'd imagine

Yes, but it's oxygen atoms in water, not elemental oxygen, so it's not going to burn anything. (At least not at typical oil temperatures. Now, if heat it to thousands of degrees, rather than hundreds, that's a different story.)
posted by DevilsAdvocate at 10:25 AM on January 22, 2004

Interesting fact: Oil and petroleum products are burned to produce carbon "dust" or "carbon black," which is then used as a cheap "filler" (sometimes along with other fillers such as clay and graphite) in rubber, such as tires, Tupper-Ware, etc. Synthetic rubber (such as trade-name: "Buna," produced by former Nazi-collaborators Bayer, who experimented on Jewish people during WWII, aka "the childrens' aspirin company) also contains petroleum products, and is often used as the "gum base" in chewing gum. Petroleum products are carcinogenic, of course.

Just an interesting fact about "carbon"...
posted by Shane at 10:28 AM on January 22, 2004

My best guess without doing the experiment and seeing what it looks like is that in the oil case you're not generating carbon by burning (ie combining oxygen from the air with hydrogen in the organic fuel to leave carbon), but rather breaking down/reforming the chemicals present into some kind of organic gook.

I think it's probably something like this. The sugars in the food do contain many oxygen atoms. This is the primary characteristic of a sugar: it's a hydrocarbon with many hydroxide (-OH) groups. Of course, the reaction wouldn't be the same as it is in the presence of excess molecular oxygen (O2), but it would produce similar products (water, carboxides, and unreacted carbon). In fact, I believe that if, in the first case, you could guarantee complete saturation of the burning food with excess oxygen, you would see little or no carbon at the end: the residual unreacted carbon is a result of "starving" the reaction of oxygen.
posted by mr_roboto at 11:06 AM on January 22, 2004

produced by former Nazi-collaborators Bayer, who experimented on Jewish people during WWII, aka "the childrens' aspirin company

Woah, a little off-topic there, wouldn't you say?
posted by me3dia at 2:13 PM on January 22, 2004

Indeed. The children's aspirin company is St. Joseph's, after all.
posted by kindall at 3:47 PM on January 22, 2004

mr_roboto is right. You're not actually burning the organic components (fats, sugars, etc.). Due to the heat of the frying oil, the atoms (C, O, H) of the organic components are more or less 'shuffled', degrading the complex proteins, fats etc. and releasing H2O and CO2. Your end product will depend on the temperature of your frying oil.
posted by swordfishtrombones at 1:51 AM on January 23, 2004