Pizza question

Factual Questions
1

(I know this probably came up before, but I have no way to search this site.)

Someone was shown on the news once who tried to find out which part of a slice of pizza gives you burns. The guy pulled a fresh pizza out of the oven and put it directly under an infrared-sensing camera. All parts were equally hot, so he declared it a tie.

But I’m sure the question is not how hot the parts are ( they of course are all the same temp in the oven. That’s how temp works in a closed system.)
The question instead is which part transfers its heat to your mouth fastest.
My own observation is that it’s the sauce.
So I’m guessing that a liquid (sauce) gives up heat quicker than a colloid (cheese).

Are there proofs for this?

2

You are correct in your observation that the sauce burns your mouth faster than the cheese or the crust, but the reason is not that the sauce gives up its heat faster, but just the opposite. The sauce holds heat better–scientists say it has a high specific heat capacity–which means it has more thermal energy per degree of temperature per unit of mass of material. Water has one of the highest specific heats of any material, as a result, substances which are high in water can contain a lot of heat. That’s why boiling water at 100 degrees C will burn you MUCH faster than air at the same temperature.

3

But water evaporates at 100C, the oil in the cheese (and certain toppings) can get much hotter than that. I have no emperical proof, but I would speculate the little pools of oil are what really gets you.

4

I always presumed the problem was the propensity of cheese to stick to flesh, thereby conducting heat in a most efficient manner.

5

Well that seems to cover the possibilities all right.
I notice nobody blames the bread part. Perhaps if we figure out what bread does that’s different we could extrapolate that in the other direction for the answer.

6

OK… Let’s line up the suspects, shall we?

:: paces back and forth, occasionally glancing manacingly at the four suspects ::
Bread: You’re light, fluffy, basically dry. Low density + High air content + low moisture gives low “burnability.” ::waves bread on:: You’re free to go.

Cheese: Basically Milk Solids and Oil. You do, however have the ability to stick to flesh, thus keeping the heat on one area and concetrating the burn. Oil (olive oil) has a specific heat of 1790 (J/kg K). :: points:: Don’t move. ::glares::

Oil: Same specific heat, less ability to stick to flesh in massive quantities. Getouddahere, but I’d better not hear anything about splatters. ::thumbs towards door::

Sauce: Basically water, with some organic solids, and a lot of sugars. So you have the ability to stick to flesh better than oil, albeit not quite as well as melted cheese, eh? But wait a minute, you are liquid at a lower temperature than cheese, so can actually stick better at lower temperatures? Hmmm… what’s your specific heat? 4200?!? That’s it! Up against the wall, punk! We got our man, er substance! Cheese, you can go, but I’ve got my eye on you. ::attempts to handcuff sauce, gets confused…::

<ahem>

What I’m basically saying, is that it’s a question of how long a substance is likely to stay on the same spot & how much heat energy it has at a given temperature. One other thing to consider: as cheese cools (by giving up it’s heat to your now burning flesh), the layer right next to your skin will cool and harden, thus acting to keep the rest of the heat away. Sauce? No such hardening.

We now return you to your regularly scheduled …uhhh… something.

7

After a couple minutes at the table the center is the last thing to cool. Right out of the oven all the pizza burns. The center is insulated by the other toppings and crust and the center always stays hot longer. The center ingrediant is going to have the potential to burn you for the longest period of time, wahtever it is.

8

I found the answer!
And it was easy.
I had pizza last night and simply used my finger to test different parts.
Not as sensitive as your mouth perhaps, but easier to see what you’re testing.
But I won’t spoil the fun for all the junior scientists out there - I leave it as an exercise for the reader. :smiley:

9

JustAnotherGeek, that was right Alton Brown-ish of you. Good show, sir!

10

So while the sauce is the actual cause of the burn, the actual criminals are the cheese/topping combo and the crust. They conspired to keep the sauce at an unsafe temperature, while fooling our hands and mouth into thinking the slice was cool enough to eat. Expect to be called as an expert witness at Mr. Sauce’s trial.

11

So it’s a conspiracy, ay? Lock 'em all up! :dubious: (pretend he’s glaring)

Actually, that’s a good way to think about how the pizza could stay warmer longer than, say, foccacia. Nifty food science experiment: test how temp changes on pizza, foccacia w/ sauce only and foccacia with cheese only.

:smiley: Why, thank you! ::blushes:: I dare say that is the higest compliment I’ve gotten on these boards! :smiley:

12

I thought I read an article about a researcher, possibly at Yale, who had proved that the sauce was kept hot by being insulated, but I can’t find any mention of this by Googling now.

13

[nitpick]

At standard pressure, pure water boils at 100 °C. Water can evaporate or sublimate at any temperature less than 100 °C as long as the relative humidity is less than 100%.

[/nitpick]

14

Joules per kilogram-Kelvin?

Bah.

No red-blooded American you settle for Specific Heat in any units other than good old-fashioned calories per gram-degree Celsius. Just like Lavoisier used. (Or would have used, if he’d had degrees Celsius. And grams. Uh, and calories.)

15

Right now fun for me would be seeing the answer without having to wait until the next time I have pizza. So spill, what did you observe?

16

I remember reading this article, too, so you’re not crazy. We’re both pretty forgetful, though, because I sure as heck can’t recall who it was by. :slight_smile:

17

I’m laughing so hard I’m crying.

Not that someone would do this experiment, but rather that I immediately know how I’d set up the experiment, what equations to use, and how to explain it… you see, I’m researching the heat flux of the ocean surface… been a long day… :smack:

Ummm, yeah, now that I think about it, what will be affected by the presense of the cheese will be 1.) the overall mass & 2.) the rate at which the heat is given off by the pizza as a whole (heat flux). So the sauce gets insulated by the cheese and the crust, since heat flux is directly related to specific heat.

Oh Gawd, I signed on to take a break! I’m a :wally

18

Your intrepid researcher is correct, up to a point. All parts of the pizza are equally hot. This is due to thermal equilibrium. The pizza (all parts of it) has attained the temperature of the oven, more or less. When removed, it tries to reach thermal equilibrium with the air, but heat transfer in air is a most inefficient business, so the pizza stays warm for a little while.

Not the case when the pizza comes in contact with the skin inside your mouth. You reporter assumes that because each part of the pizza is the same temperature, they all burn your mouth equally. But as we all know, if the too-hot slice is consumed cheese-side-up, the roof of your mouth sustains horrific first-degree burns resulting in blisters, whereas your tongue remains relatively unscathed.

JustAnotherGeek has it with the specific heat, which is the amount of heat energy per unit mass that must be transferred into a substance to raise its temperature one degree.

So when the 100+ Celsius pizza hits your 37- Celsius mouth, some of the stuff on top, with a higher specific heat than the crust, begins transferring large amounts of heat energy to your palate in an attempt to drop its own temperature and reach thermal equilibrium with it. That’s what hurts.