Cooking Time

[Shel_B]

In a way this is more an academic question than anything, but curiosity has prompted me to ask. Toots makes a nice pot luck dish (eggs, spinach, corn, the ubiquitous cream of mushroom soup, etc) that we both enjoy for its ease of preparation and flexibility. She prepares it in an 11" x 7" Pyrex dish. I have a Corningware casserole with square dimensions, 8.25" x 8.25" approximately, which is slightly deeper than her Pyrex. The overall volume of the two dishes is about the same. Given similar volumes, how do the dimensions effect cooking time? Are there situations where dimensions are more critical than others? And what about shape, such as round v square, assuming similar volume? Just curious ... Thanks!

[Norm Matthews]

No one has attempted to answer this question yet and it has been posted since earlier this morning. I have seen math people put out numbers on things like this but they doing a math exercise and weren't really bakers. I am not a math person by a long shot and I bet as soon as I say what I think, someone will come along and argue with me but just remember I'm giving my limited opinion because no one else has done so yet.

Since the same recipe is going into a relatively similar container- both ceramic glass, both with four corners and the exact same volume, I guess they both will bake at about the same time. The smaller one may take a little longer because the depth is a little greater but really it isn't critical. Just bake until set in the middle.

As for your question about shape, this is a quiche or casserole, not a brownie or cake so it still isn't critical as long as you can tell when it is set in the middle. Cake-like baking in cornered vessels tend to cook at the corners faster because the heat travels in from the sides to the middle of the corner faster than it will travel in from the straight side to the middle while a round container will cook more evenly in to the center... The outside still cooking faster than the center. That is why a cake rises higher in the middle because it has not set and stopped cooking as quickly as the outside diameter.

[Shalmanese]

As a very general rule, cooking speed goes up as the square of the thinnest dimension. A much better way of doing it though is to rely on physical signs of doneness, not time. For egg dishes, you want it to be slightly jiggly in the center but not liquid when you take it out of the oven. For baked goods, you can use the toothpick test and for meats, a digital probe thermometer.

[IndyRob]

I have seen math people put out numbers on things like this but they doing a math exercise and weren't really bakers. I am not a math person by a long shot and I bet as soon as I say what I think, someone will come along and argue with me but just remember I'm giving my limited opinion because no one else has done so yet.

Okay, I'll play the math guy and back you up. The difference between the (top and bottom) surface areas is 77 sq. in. (11x7) vs. ~68 sq. in. (8.25x8.25) We don't know the thickness of the dish in either case, but because the depth is directly proportional to the area (assuming you're using the same recipe), we know that the smaller pan will be piled about 13% thicker.

As you say, the smaller one should take a little longer. Because the heat transfer will most likely be quicker from bottom to top/top to bottom (much thinner) than from the sides. Then again, a square pan will conduct heat more quickly to the center from the sides than an oblong one (a circular one would be most even as heat from the sides goes).

So with the square pan we have a quicker sideways heat transfer, but slower up and down. We also have a ton of other variables we haven't accounted for (insulation of the oven... just a bottom heating element or top and bottom...gas vs. electric...Is the spinach fresh or thawed from frozen and squeezed?)

So the math can guide us, but we still have to be cooks. And as Shalmanese suggests, the eggs seem to be the things to watch here. But all-in-all, a little more time for the smaller, thicker dish seems right.

Edited November 29, 2011 by IndyRob (log)

[dcarch]

It also depends on what kind of stove. Electric heats by conduction, and gas by convection.

Then, open surface area enters into calculation. The larger area creates more evaporation (laten heat loss), unless your food is covered with oil on the top layer.

The surface area of the cookware follows the "Black body" radiation law, i.e. the larger the surface area, the more radiant heat lost (sensible heat loss).

dcarch