Greeting Science Squaddies! Welcome to the maiden voyage of the SuburbanJoe Science Squad, an intrepid group of knowledge seeking adventurers. Good to have you along. I should point out that while writing this post I'm watching my "Butch Walker Live in Budokan" DVD, thereby keeping to two of my resolutions at once. Impressive, I know. For the record, for those of you not morally opposed to rocking out at dangerous levels, you could do worse than buying Mr. Walker's DVD. I'm not sayin', I'm just sayin'. Do not be scared by the fact that it's from Sony. As far as I know, it has not installed any rootkit software on my DVD player, however if porn mysteriously shows up in said player, blame it on the hackers.
Today's scientific inquiry comes from a conversation me and the missus had many years ago. As I was cooking, and stirring something on the stove with a wooden spoon, Linda asked me why people use wooden spoons instead of metal spoons. I told her that some people think that metal imparts a bad taste to the food. She then uttered the classic question, "Then why don't people use wooden pans." That's my wife ladies and gentlemen.
As I was coming up with my first entry for these posts, she recommended I write about why people don't use wooden pans. The more I thought about it, disregarding the obvious reason of course, I thought that it was an excellent question, so today we tackle the question of the ages:
Why Don't People Use Wooden Pans?
One caveat before we get started. I'm not a scientist, I'm just a guy who likes finding things out. I say this because I don't want to give the impression that the answers I'm giving here are the end all and be all to the question at hand. It's just one explanation. The beauty of the sciences is that often times, there are multiple scientific explanations to things and if you extend your view of fields that the term "science" encompasses, you can find even more answers. So far, I've found that for every answer I find, I find 5 more questions, but that's a good thing. OK, caveat over. Let's roll.
The first thing to talk about is that heat will always go from a hot object to a cold object, provided that the system isn't so well insulated as to prevent the transfer of heat. This is why, when ice is placed in a cup of hot water, the ice melts (gets warmer) and the water gets a little cooler, rather than the ice getting colder and the water getting hotter. That would be some fucked up shit. Heat transfer is dependent upon the substance that is between the hot thing and the cold thing. In our example, it would be whatever the pan is made of. Every value has a constant called the thermal conductivity (k) that defines the rate that energy will transfer through a slab of material of a given size and thickness at room temperature. Bigger numbers mean that heat transfers more quickly, lower number means a slower transfer. For the record, this constant is also a good measure of electrical conductivity, with some exceptions, if that's how you roll.
For the sake of our discussion, we're going to assume that our non-wood cooking pan is made out of cast iron. I don't know how the various non-stick coatings would affect heat conductivity and such, so I'm going with cast iron which is a little more manageable. Wood is just, well wood. If you can find a tree out there that acts like metal, feel free to let me know and I'll specify a less conductive wood accordingly. Good luck.
OK, so, thermal conductivity. For cast iron, the thermal conductivity value is 55 (forgive me for not using units. Physics teachers everywhere are cringing.) In comparison, wood has a thermal conductivity that ranges from 0.04 for balsa to 0.35 to fir. As you can see, heat goes through cast iron like a hot knife through butter, and through wood like something less hot and less buttery. The difference in heat conductivity also explains why you can pick up a stick that's burning on one end and not have any adverse affects. Pick up an iron rod that's glowing on one end and most likely you won't be shaking hands with anyone for some time. Now, one thing to keep in mind is that you don't want too high of a thermal conductivity for your cooking surface, as you want to allow the heat to diffuse throughout the pan's surface as well as transfer to the food. Otherwise you'll only get heat right over the heat source, which leads to scorching and bad feelings.
It's not really fair to compare wood and cast iron in terms of thermal conductivity. Cast iron is a (mostly) pure solid with a crystalline structure that just begs to conduct heat. Start agitating the atoms and electrons at one end and those vibrations will move through the substance and heat up the whole thing. Wood on the other hand, is a paella of water, cellulose, lignin and other loosey-goosey compounds. That being said, here's your simple answer as to why there are no wooden pans, wood has a shitty thermal conductivity value, and therefore would not transmit heat from the heat source to the food effectively enough to cook well, if at all. Strangely enough, you'd be better off with a pan made of ice (k = 2.2). Chew on that one.
Also, people use wooden spoons so as to not conduct heat away from what's being cooked, which can happen with a metal spoon. That's not really a concern when making stew, but when making candy you can end up screwing up your crystallization. That's right, somewhere out there there's a guy at the 3 Musketeers factory stirring a big vat of nougat with a massive wooden spoon.
That's not to say that there aren't wooden pans out there. Go to any gourmet food stores and you'll see fancy-pants cedar planks for grilling. The idea is that you soak the plank overnight, fire up the grill, place your meat (usually salmon) on the plank and grill with the lid closed. As the meat cooks, the plank smokes and chars and adds some smokey goodness to the meat. You can then serve your meal on a smoking, charred hunk of wood, which then makes your guests smell like smoking, charred hunks of wood. Now, as the lid is closed in this case, it's the indirect hear circulating through the grill that cooks the meat, rather than heat being transferred from the heat source through the plank and to the meat. Given that this is the case, the pan in question is more like a baking sheet and less like a frying pan. If you want to go this route with your baked goods, more power to you, but forgive me if I skip the cookies.
Next week: On Wood and Melty Things
Sources: Fundamentals of Physics, Extended Edition, Halliday, Resnick & Walker
Wikipedia - Thermal Conductivity
Thermal Conductivity - Ulf Bolmstedt
The Physics Hypertextbook - Conduction, Glenn Elert