Does grilling change cheese?
January 9, 2008 10:31 PM   Subscribe

My SIL insists that cheese somehow gains more fat when it is heated, because "the fats are unstable and more fat is released when cheese is grilled". Therefore, according to her, a grilled cheese sandwich is more unhealthy than a plain cheese sandwich. I think this is bonkers, but can't find any evidence to wave in her face. Any ideas?
posted by indienial to Food & Drink (45 answers total) 6 users marked this as a favorite
Well, to point out the obvious, a grilled cheese is usually grilled with some sort of oil or fat (like butter) which would add to the fat content a bit.
posted by RikiTikiTavi at 10:37 PM on January 9, 2008

The question isn't about added ingredients.
posted by null terminated at 10:38 PM on January 9, 2008

Where does she think this fat goes when she eats un-heated cheese?
posted by nathan_teske at 10:54 PM on January 9, 2008

So her argument is that cooled/room temperature cheese somehow "locks away" a portion of its fat from normal human digestion? I hope that's it, because I don't think there's a special cheddar wormhole where fat from elsewhere in the universe is pumped into cheese whenever it's heated. Does she also argue that the process is reversible: if the cheese cools down, does the fat get locked away again, or is she saying that once cheese is heated, it's permanently fattier? And what's the threshold temperature at which dairy fat becomes more bio-available?

If she's arguing that hot cheese going into your digestive system is more easily used by the body, then the burden of proof is on her to find peer-reviewed research that supports this. I know that there is some evidence showing that the calcium in dairy foods binds with a significant portion of your fat intake and is excreted in your crap. Maybe she's mixing up that research with something else suggesting that heat in general releases more nutrients in food: for example, the beta-carotene in cooked carrots may be more bio-available than it is in raw carrots.
posted by maudlin at 10:56 PM on January 9, 2008 [2 favorites]

Explain to her conservation of matter.

There is nothing about heating up cheese that makes more or less fat appear. It just looks that way because the fat turns runny and soaks in the bread. Ask her if melter butter has more fat than solid butter. Butter is the same milkfat as in any cheese. Ask her if she'll eat sticks of butter with you because they're healthy because they're not warm. Post pics.
posted by OldReliable at 10:56 PM on January 9, 2008 [4 favorites]

Fats don't just spontaneously appear out of nowhere. While it's true that cooking can alter the chemical structure of foods, it's typically in less fundamental ways, like denaturing proteins. Converting other molecules into fatty acids is likely to be a multi step process that even your body only accomplishes with the help of a host of enzymes and much expenditure of energy. That frying pan doesn't have much of a chance.

So yes, your girlfriend doesn't appear to know what she's talking about.

The first two posters make good points, because grilled cheese requires adding butter to the outside of the sandwich. This means that when you look up the nutrition facts for a cheese sandwich vs. grilled cheese sandwich, the fat content will likely be higher in the latter.
posted by chrisamiller at 11:00 PM on January 9, 2008

I think you're going to have difficulty finding reputable sources explicitly denying this idea, for the simple reason that it's too ludicrous a notion for the reputable sources to have even considered. What does it even mean? How can something "release" more fat than it contains?
posted by baf at 11:00 PM on January 9, 2008 [1 favorite]

Best answer: cheese somehow gains more fat when it is heated

Cheese has whatever fat is in it when it is packaged. Heat, if anything, breaks down fats — this is why you keep cheese and butter in the fridge, so that they don't go rancid as quickly — but I doubt there's enough heat in melting cheese to do this to any significant degree.

The idea of heat is to release aromatics — warm cheese is more fragrant and tastes better than cold cheese.

Perhaps the better question is: Does melted cheese get digested differently, so that your body metabolizes more of the nutritional content of the cheese ("absorbs more fat")?

Warm, melted cheese might be chemically digested more efficiently than unmelted cheese, as digestion enzymes work better at body temperatures. Cold, unmelted cheese might need to be warmed up — but chewed up bits of unmelted cheese sitting in your stomach will probably warm up fast enough that there's no significant difference in enzyme efficiency ("turnover rate").

Once the fats from the cheese arrive in your upper intestine, they are already at temperature equilibrium (body temperature) at this point and will be readily absorbed, whether originally part of melted or unmelted cheese.
posted by Blazecock Pileon at 11:06 PM on January 9, 2008

If she's a grown woman and she doesn't understand conservation of matter, I doubt you're going to have much luck, unless you get a mutual acquaintance who is a physicist or chemist or nutritionist to explain it to her.

This reminds me of my college roommate, who insisted that meat expands when it's cooked due to "fire pumping it full of 'heat molecules'".
posted by arianell at 11:07 PM on January 9, 2008 [6 favorites]

Explain to her conservation of matter.

Thats not really relevant here. I also don't see the need for the dismissive tone. Her question seems reasonable to me since heating can alter the chemical composition of substances.

For example, heating can induce the creation of trans-fats although there's no evidence that this occurs in any significant degree.

If she's a grown woman and she doesn't understand conservation of matter,

Again, This is not about conservation of matter. I think answerers here are betraying their own ignorance.
posted by vacapinta at 11:12 PM on January 9, 2008 [7 favorites]

Heating up ≠ burning

frying pan ≠ oil hydrogenation vat

grilling ≠ enzymatic reaction

Where exactly is the extra fat going to come from? Like I said, because the fat in the cheese melts and you can suddenly see lots of oil, she thinks that its worse for you, or maybe that there is more of it. She is wrong.
posted by OldReliable at 11:34 PM on January 9, 2008

There is nothing about heating up cheese that makes more or less fat appear.

The fat in cheese does tend to liquefy and separate out when heated. That's one of the reasons why processed cheese was invented: to prevent this tendency.

So yes, speaking literally, oil does appear when the cheese is heated. But I don't see why it would be worse for you in liquid form, any more than melted butter is worse for you than solid.
posted by ottereroticist at 11:39 PM on January 9, 2008

Question: do we absorb all the fat that we consume, or most of it?

If 'most', then does grilling fat increase its ability to be absorbed?

Either way, it should be negligible. Its the big things, over long-term which matters most to weight control.
posted by gttommy at 12:19 AM on January 10, 2008

Best answer: Blazecock Pileon has your best technical answer. IANAC, but from what I understand, the fat referred to in cheese is actually chemically termed triglycerides (compounds with a glycerol molecule esterified with three fatty acid molecules).

By adding heat to the cheese you're going to breakdown the triglycerides into their component fatty acids and glycerol molecules, at which point they will volatize (i.e. the ashes Blazecock refers to in his second post).

Now, I'm more fuzzy about the rest, but here goes. What I described above is only going to occur when you reach the triglyceride's boiling point. What I think will actually occur with your real world scenario is that the you are altering the state of matter that the triglycerides are in. They go from a solid state, i.e. a cheese slice, to a semi-solid state, i.e. a cheese mush between two pieces of bread. If you continue heating the sandwich, the cheese will eventually become liquid. If you continue, you start to breakdown the triglycerides and we're back to the second paragraph.

The bottom line is that the heat applied to the cheese does not increase the amount of fat in the cheese. If heated enough, it actually reduces the amount of fat as energy gets released by the breakup of the triglyceride molecules and the free fatty acids and glycerol burn up as heat. As Blazecock mentioned earlier though, it's doubtful your cook the cheese enough to get to that point (there's the whole thing with the bread burning and what not).

Your SIL may be confusing the terms fat and fatty acid. Fatty Acids are unstable in nature because they are highly reactive. Fat in the form of triglycerides, on the other hand, is one of the most efficient forms of energy storage on the planet. The fact that it is utilized by the majority of biological organisms should lend it some credibility in this regard.
posted by herda05 at 12:26 AM on January 10, 2008 [3 favorites]

If anything, heating (melting) cheese separates the proteins from the lipids, making the fats even easier to isolate and sop up (with a paper towel).

However, she needs to brush up on The Conservation Of Matter.

If I was capable of increasing the stored energy of a food by heating it up, I could solve most of this world's ills, if not get all Cheney on you.
posted by sourwookie at 1:29 AM on January 10, 2008

My mum is convinced this is true as well, and has been for many years. I never lived it down after she came to visit my student share house and told the med and science students that they shouldn't melt cheese in the microwave, because "melting cheese is exactly the same as frying it". Nothing anyone said would convince her otherwise. It makes me feel almost relieved to know I'm not the only person who's had this argument!
posted by andraste at 3:21 AM on January 10, 2008

It seems like it might also be worthwhile to point out to her that cheese is heated up to body temperature in the course of ingestion anyways. If this idea of hers is related to the way that separated oil "sweat" appears on the surface of some cheeses as they're heated up, you might be able to demonstrate to her that this also happens at body temperature, or room temperature for that matter.
posted by XMLicious at 3:34 AM on January 10, 2008

These is the way I would explain it, after making sure conservation of matter is understood: If before grilling there are 5 grams of fat in the cheese, and after grilling there are 7, two grams of something must have transformed into 2 grams of fat. What is this something? Can you think of anything in cheese that under normal grilling conditions would transform to fat?

If grilling increased the fat content of cheese, calorie limited cheese eating cultures would have eaten nothing but grilled cheese for the last few thousand years. A grill as a cow: Turning the inaccessible calories locked in the cellulose of firewood into digestible cheese fat.
posted by Dr. Curare at 4:02 AM on January 10, 2008

Actually, the raw food people make a case for some of this, although it is likely bunk. The argument is that oxidized fats increase the risk of atherosclerosis [Taylor et al. 1979, Kummerow 1993, Kubow 1993, O'Keefe et al. 1995]. There is not any kind of scientific consensus that this is fact, but there is at least some study on point. However, even if you accept that oxidized fats increase your risk of arterial disease, it isn't clear that simply heating fat will get you there. There is better evidence that suggests that rancid fats are more dangerous. The only study I am aware of that confirmed health risks from heating fats is Greco AV, Mingrone G. where they heated soybean oil to 240 degrees for an hour. There are also studies that fail to confirm this effect.

So, pretty clearly, just melting cheese isn't going to get there. However, those of you rejecting it on some kind of Newtonian basis are off-base. The basic underlying process that heating fats leads to increased oxidation leads to heart disease is at least possible and there are studies that support it. However, the only studies that suggest it require deep fat frying temps to get there. I will concur that the SIL's idea that fat is somehow formed by heat is pretty much crazy-talk.

There are lots of studies that reject this conclusion. I'd suggest that you Google "thermooxidized fat" to find all you can stand.
posted by Lame_username at 5:27 AM on January 10, 2008

Show her this thread.

Also, realize that there are some arguments that aren't worth bothering with.
posted by electroboy at 6:20 AM on January 10, 2008

If she's a grown woman and she doesn't understand conservation of matter, I doubt you're going to have much luck...
However, she needs to brush up on The Conservation Of Matter.
Don't be dicks. Most people don't remember or understand their one or two high school exposures to conservation laws. Hell, most people don't know where the seasons come from. Atop which, this is a reasonable question she has, if perhaps badly phrased: is it possible that heating cheese converts this and that into that and this, making it worse for you to eat in some way? It's true of Teflon. She's apparently not asking whether fat is created from scratch, she's guessing that what goes down your gullet in a grilled sandwich is chemically different from the other thing. Not a bad guess, eh?

maudlin recognized the SIL's thinking right away. Well-played.

I would point out that indienial was unable to win this argument with his in-law, since all he had at his disposal was 'this is bonkers.' Let's hear one for rational fucking thought.
posted by waxbanks at 6:40 AM on January 10, 2008

So yes, your girlfriend doesn't appear to know what she's talking about.

It's not his girlfriend, it's his sister-in-law.

Thanks, waxbanks, it's not like the SIL is the only one who couldn't explain it. What's with the science snobbery? There's no need to treat someone like an idiot just because they don't understand a scientific principle. Some more kindness in AskMe, please?
posted by agregoli at 6:53 AM on January 10, 2008

Not sure why this comment was deleted, but by way of an extreme metaphor:

Taking a blow-torch to cheese will not add fat, but in fact will oxidize the fat in the cheese, leaving low-fat ashes.

Another extreme analogy is that burning (oxidizing) a candle does not add wax ("fat"), but instead consumes it.

Melting, or burning, are both forms of adding heat energy.
posted by Blazecock Pileon at 6:53 AM on January 10, 2008

Tell her not to worry, and I should know. -- truly yrs, FourCheeseMac
posted by fourcheesemac at 7:24 AM on January 10, 2008

Your SIL is clearly insane.

Seriously, though, isn't it far more intuitive that heating something would burn away excess fat rather than adding fat, like Blazecock Pileon's candle and wax analogy? Fat can't just appear from nowhere; in your SIL's 'explanation', it seems to come out of the air, which is clearly nonsense. If she is saying that melted fat is worse than solid fat, she may somehow be linking trans fats and saturated fats with the heating process and drawing a conclusion from that? I guess. Still out there, though.

Try this: Ask her if she thinks that crispy bacon has more fat than raw bacon, too, by the same reasoning. Then fry up some bacon and layer it on paper towels. You can see the fat dripping off the bacon, showing up on the paper towels. So, logically, shouldn't the bacon have less fat now, rather than more?

Paging Mefi's own Asavage to please please please put this on Mythbusters!
posted by misha at 8:08 AM on January 10, 2008

Here's an empirical approach to your problem that doesn't involve chemistry or physics explanations.
I used Epicurious for the recipe for a grilled cheese sandwich, then I looked up the ingredients on the Calorie King site for their nutritional information (such as fat content). Calorie King also has the nutritional information for completed Grilled Cheese sandwiches as well. Here's what I came up with:

Epicurious Recipe

2 slices Cheddar, American, or Swiss cheese
2 slices white bread
2 tablespoons butter

From Calorie King
2 2 (1 oz) Slices of American Cheese: Tot Fat: 17.5g Sat Fat: 11g Chol: 53mg
2 (0.9 oz) slices of white bread: Tot Fat: 1.6g Sat Fat: 0.4g Chol: 0mg
2 Tbsp of butter: Tot Fat: 23g Sat Fat: 14.6g Chol: 61mg

Total: Tot Fat: 33.7g Sat Fat: 26g Chol: 114mg

Grilled Cheese from the Senior Menu at Denny's (7 oz) (I figured that would be a reasonable approximation for the above recipe):
Total: Tot Fat: 30g Sat Fat: 12g Chol: 45mg

You or others are free to tweak and vary things, but it seems that a grilled cheese sandwich is more healthy than its constituent ingredients. About the only way I can see the SIL's point making sense is if she's considering a cheese sandwich to be sans butter?
posted by forforf at 8:15 AM on January 10, 2008

That's 2 slices of cheese, not 2 2 (the nutritional data is correct).
posted by forforf at 8:17 AM on January 10, 2008

OldReliable: Explain to her conservation of matter.

arianell: If she's a grown woman and she doesn't understand conservation of matter, I doubt you're going to have much luck...

sourwookie: However, she needs to brush up on The Conservation Of Matter.

Indeed, this woman is being very foolish. She is like unto those silly people who claim that you can "make" steam by heating water. Don't those ridiculous sots know anything about the conservation of matter?

Seriously, however, my simple answer to her would be: the heat is never enough to change the fat significantly. Also, cheese is heated when it's being made, so whatever fat there is has already been rendered into it. There's also the compelling and well-known commonplace that milk is already full of fat. It may well be that the making of cheese is the changing or removing of that fat, but it seems to me that the opposite is the case.
posted by koeselitz at 8:49 AM on January 10, 2008

Why do you need any evidence? She is the one with the extraordinary, physics-defying claim; let her provide the evidence for her position, or else admit she is wrong.
posted by kindall at 9:02 AM on January 10, 2008

forforf the comparison you are making is flawed, the denny's sandwich could be made from different brands/types of cheeses, breads, butter and/or magarine and could use differing amounts. Different cheeses (even brands) can have varying amounts of fat/calories so you actually have to use the specfic nutritional information for each specific item, and even these numbers are subject to flaws (slight variations from rounding numbers during or after calculations, as well as the fact that these items come from nature (hopefully) and nature isn't totally consistant (one batch of wheat can have lower protein than one grown in a field 2 miles away)

I am a chemist (but not your chemist). The cheese will not gain or lose any calories through cooking. In order for any food to change the amount of calories in it has to come from mechanical means (ie fat dripping off a steak on a barbeque) or actual combustion (burning it, this breaks chemical bonds and is called oxidation, this process releases heat/energy and calories are a measurement of energy). Regular cooking supplies enough energy to cause phase changes (aka going from a solid to a liquid) and disrupt intermolecular bonds (denature protein, aka cook meat) which can then reform causing no net change (very near no net change) energy wise but nearly all molecular/covalent bonds which is where the vast majority of calories are contained can't be broken down by the heat of normal cooking temperature.

Simply put calories in = calories out, no real addition or subtraction happens through simple heating
posted by estronaut at 9:34 AM on January 10, 2008 [2 favorites]

It seems to me that heating something up might ultimately cause you to burn fewer calories than not heating it up -- ie, the calories that would otherwise be expended to replace the body heat that was lost to bring the unheated food up to body temperature while it's in your stomache. This would be so tiny as to be unnoticable in a daily diet, but it's probably calculable, ie, how much energy does it take to bring a sandwich up from room temperature to body temperature.

And thinking that heat might somehow alter the chemical composition of something isn't exactly el-whacko what-the-fuck-did-you-never-take-a-science-class-in-high-school thinking. After all, in your high school science classes, you do experiments over bunson burners for a reason.
posted by jacquilynne at 9:57 AM on January 10, 2008

estronaut, you are absolutely right ... but my gut feeling is that indienal's SIL would be more swayed by having something physical to show vs. trying to explain to her abstract physic theories or proper scientific method. If her SIL did turn a critical eye towards it, well then that would be a huge benefit, since she'd be more likely to look at her conclusions with a critical eye as well.
posted by forforf at 10:06 AM on January 10, 2008

In the SIL's defense, I just want to point out that a grilled cheese sandwich feels fattier than a cold cheese sandwich, even allowing for the fat it was grilled in. Not just in your mouth, but in your body afterward. You really feel like you ate something fatty. For a cleaner example, imagine how different you might feel if you ate (1) a hunk of cold cheese and a glass of white wine, versus 2) a similar quantity of fondue (cheese and wine melted together).
posted by Enroute at 10:13 AM on January 10, 2008

Maybe it's a perception problem. Warm cheese certainly tastes fattier than cold cheese.
posted by demiurge at 10:15 AM on January 10, 2008

Aquaman: The only explanation for cheese getting fattier when heated is magic cheese.

So the interesting, if utterly unscientific, notion that fat is an element that cannot be created or destroyed continues apace.

This is a more difficult question than it seems at first.

Do we have any biochemists here? At this point, the question seems to be:

How is fat created? Does this process involve heat? If it does, then does it involve the same kind of heat that happens when I grill up a cheesy-good samich?
posted by koeselitz at 11:09 AM on January 10, 2008

estronaut provided a reasonable answer above.

Though I to am amazed by phrases like "physics-defying" and the continued invocation of "Conservation of Matter."

I have news for all these people who slept through physics class: Conservation of Matter states that its ok for the cheese sandwich to turn into a beam of light - which I doubt has any fat content at all.
posted by vacapinta at 11:17 AM on January 10, 2008 [2 favorites]

Yes, it is OldReliable, arianelle, and sourwookie (and the people who favorited their comments) who need to brush up on the conservation of matter, specifically what it doesn't say. They are expanding the principle far beyond what it actually says, much like creationists try to expand the second law of thermodynamics (actual version: no entropy decrease in a closed system. Creationist version: no entropy decrease in a closed system; also, no entropy decrease in an open system without action of an intelligent agent.)

Conservation of matter does not prevent chemical compounds from being created or destroyed. It is certainly possible to create fat where there was none before--but it generally takes a living organism, or a lot of enzymes, or a complex laboratory set-up (or more than one of the above). Fats are fairly complex molecules. It's not happening in your SIL's skillet.

Do we have any biochemists here?

Yes, I have a bachelor's degree in biochemistry.
posted by DevilsAdvocate at 11:50 AM on January 10, 2008

...and, looking around a bit, there are sensible answers. Blazecock Pileon and herda05 have some great answers up above. Looking around on wikipedia (the tool of the foolish nonexpert like me) I think maybe you could offer this answer:

Since fats are chemically "a triester of glycerol, an ester being the molecule formed from the reaction of the carboxylic acid and an organic alcohol," (more briefly, an interesting combination of carbon, hydrogen, and oxygen) creating fat would involve chemically bonding carbon, hydrogen, and oxygen rapidly. (I'm no chemist, but it seems to me that such a complex activity would not likely be accomplished in my humble frying pan.) Now, fat in and of itself is not a bad thing. But it is less useful for the body, less healthy, if (a) the carbon atoms have become fully saturated with hydrogen atoms, and therefore no further bonding (the essential power-plant of fat, I think) can take place -- this fat is called saturated fat, and said saturation seems to be the effect of the hydrogenation that creates trans fats. Again, I'm no chemist, but it seems unlikely that mere frying could increase molecular bonding in that way, much less replicate the work of Wilhelm Normann.

So: you can tell her that.
posted by koeselitz at 12:14 PM on January 10, 2008

Or, on preview, what DevilsAdvocate said.
posted by koeselitz at 12:16 PM on January 10, 2008

Best answer: koeselitz, I have a Ph.D. in biochemistry.

How is fat created?

The way fat is made in living organisms is quite complicated, involving many steps catalyzed by enzymes (proteins that coax various chemical reactions to go the way the cell needs them to, rather than the way they would go if you just dumped all the ingredients in a beaker and heated it up).

The atoms that go into the fat molecules have to come from somewhere. Usually this involves breaking down molecules we get in our food, like sugars or other fats, to make small precursor molecules that get hooked together by the enzymes mentioned above. The breakdown steps are also accomplished by enzymes, albeit different enzymes from the ones involved in synthesis.

Does this process involve heat? If it does, then does it involve the same kind of heat that happens when I grill up a cheesy-good samich?

Thermodynamically speaking, pretty much every chemical reaction involves heat (Google "Gibbs free energy" if you want to get hardcore). The chemical reactions of fat biosynthesis involve heat, but on an infinitesimal scale compared to your frying pan. Some of the reactions produce heat, others "soak up" heat, but this all occurs at lukewarm body temperature, so that should give you some idea of what kind of heat we're talking about.

One more thing to keep in mind is that the calorie we talk about when discussing food and diets is actually a capital-C Calorie = kilocalorie = kcal (= 1000 of the calories that chemists and thermodynamicists use). This factor of 1000 confuses the hell out of everybody, since we're often sloppy about specifying whether we mean a scientific calorie or a kcal (diet calorie). If a chemist tells you that a certain reaction liberates 300 calories of heat, s/he means a real calorie. If you eat a snack that contains 300 calories, that's actually 300 kcals (= 300,000 real calories). The underlying idea is the same (i.e., the food contains a certain amount of energy which can be converted to heat), but the units screw everybody up.

I hope this helps!
posted by Quietgal at 1:26 PM on January 10, 2008 [1 favorite]

But is the fats -> trans fats argument valid?
posted by Krrrlson at 2:01 PM on January 10, 2008

I am seeing the SIL's assertion a bit differently than is being discussed here, possibly because I know people who think this way. While I think she is wrong, here is what I think might be HER argument (and if it is not originally, the SIL might arrive at this, so having an answer would be good).

Imagine the fat in cold or room temperature cheese as wearing armor. As long as the fat is wearing armor, the body cannot process it. It simply passes out of the body. Also imagine that 98.6 degrees is not enough heat to get the armor to come off.

Now imagine that say, 110 degrees is enough to get the armor off the cheese, and the SIL believes that making a grilled cheese happens at 110. It is not that the fat is being made, but as noted upthread, "unlocked". I think a more appropriate response to this is to present evidence that the fat is not armored or locked in the first place.
posted by oflinkey at 2:46 PM on January 10, 2008

Response by poster: Oflinkey- yes, that's pretty much the theory behind her argument as far as I can tell, and the difficulty was in making her believe that you can't "unlock" fat, that it is either there or it is not.

"I would point out that indienial was unable to win this argument with his in-law, since all he had at his disposal was 'this is bonkers.' Let's hear one for rational fucking thought."-
Waxbank, that wasn't the entirety of my argument, just a summary. Never fear, rational thought is alive and well in my household. Some of the time, anway.

Blazecock Pileon, Herda05 and Quietgal- you rock! Who'da thunk a debate about cheese could get so complicated?
posted by indienial at 4:55 PM on January 10, 2008

Aw shucks, indienial! Biochemistry has a long and noble association with fine grub, especially beer and other fermentation products like cheese ("enzyme" comes from the Greek "in yeast").

Krrrlson, I think the argument you're referring to is that heating the cheese might turn regular (cis) fat into trans fat. This isn't my field, but looking at the chemical structures on this page, I'd be amazed if simply heating cheese would cause cis --> trans isomerization of its fats. It is difficult to break double bonds, and then to make the double bond re-form (as opposed to oxidizing) would be even trickier.

This is the kind of thing that chemists have to work pretty hard to accomplish, and a simple frying pan is not going to provide the right conditions to favor the isomerization reaction. In addition to high temperature you need a reducing (low-oxygen) atmosphere and high pressure, according to that Wiki article on how trans fats are manufactured in the first place.

I don't have direct experience and I'm too lazy to look for references, but based on general chemistry I'd say that heating cheese in a frying pan would not turn cis fat into trans fat to any detectable level.
posted by Quietgal at 7:52 PM on January 10, 2008

Best answer: Wow. The gift of scientists--to make simple concepts amazingly difficult, if not impossible, to grasp.

Love the conservation hissy-fit: not only is the Law of Conservation of Energy unnecessary for this conversation, it's also being taken out of context wildly. Yes, the value of (matter+energy) will always be constant in the typical frying pan system, but that fact is irrelevant. Heating a molecule up can always cause it to break into smaller molecules, some of which may be harder to digest or unhealthier. I think that's what the original question is asking.

Of course, with enough heat the fats (triglycerides) can break into smaller pieces. [They can also turn into gas, or plasma, too. If you're cooking with plasma, you won't get a chance to worry about clogged arteries.] Now, I Am A Biochemistry Student in his final undergraduate semester and I've not studied metabolism in detail (that's coming up this year), but I can serve you up my $0.02, trans-fat free.

- Heating up fats causes them to breakdown. It takes a lot of energy (heat) to do so. As in, more than the energy to melt cheese.

- When fats breakdown, they're called "damaged." They are not trans-fats. If you want more of a techincal explanation, under great stress a triglyceride "melts" into free-radical species, which is a chemical license to go wild within a system (hence the name, maybe?). The generated radicals attack any remotely nucleophilic portion of a molecule, and this leads to polymerization (also bad), but not to cis-trans isomerization. Due to the structure of fats (extremely long hydrocarbon chains which would cause major steric hindrance if you tried to bend them into "trans" formation), heating them will actually cause radicals to form before the molecule goes from cis-->trans.

This type of analysis is important for something like heating cooking oils, hence why some are considered "healthier" than others (recall that cooking oil is basically bottled unsaturated fat). But not for a cheese sandwich, for the love of Provolone! There's simply not enough heat present to make radicals of the fats in a cheese slice. So, there will not be a significant caloric difference.

And in general, fats never jump cis --> trans, but they can make some nasty things when they're under stress. I have not personally worked with heating up fats, but someone with a PhD. has, and she says the same things.

Phew. This is an intense subject matter, but I'm not really surprised--behold, the power of cheese.
posted by BenzeneChile at 7:06 PM on January 11, 2008 [2 favorites]

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