Temperature of a baked cookie-metal pan vs. stoneware

[Terri1]

My daughter is doing a project that compares the internal temperatures of cookies baked on a metal pan vs. a stoneware pan. They were baked at the same time (same temp) for the same length of time. Her hypothesis was that the cookies on the metal pan would have a higher internal temperature because metal conducts heat better than the stone. This has turned out to be incorrect. Can anyone help me with why this happened? She would like to explain in her project, why her hypothesis was wrong. Thanks!

[rmarz]

Terri1 - I'm certainly not a cookie cooking expert, but one question I'd like to ask pertains to the initial temperature of the baking pans, both metal and stoneware. Were they at room temperature when the dough was spread out then put into the oven, or were they pre-heated in the oven? Obviously the stoneware has a much higher thermal mass than a thin metal pan, and would provide more oven temperature heat than the thin metal pan. Perhaps if you can explain the procedure it will help understand the result.

Rick Marz

[Terri1]

The pans were both room temperature when the cookie dough was put on and when they were put in the oven. Yes, the stoneware pan is definitely thicker, about 1/2" compare to the metal pan, which is just a normal cookie sheet, maybe 1/8" thick. Do you think the stoneware cookies were hotter because there was more stoneware under them emitting heat? Another thing that is strange to me is that the stoneware cookies, although a much higher temperature inside, came out still gooey after the cooking time, while the cookies on the metal pan were fully cooked. Any ideas you have would be appreciated. Or any suggestions for resources. Thanks!

[rmarz]

Terri1 - I think I can fit an explanation to your findings. With both cookie sheets at room temperature as the beginning state, the metal sheet conducted heat to the dough faster and baked the cookie faster. Ultimately, the internal temperature of both batches would approach the internal temperature of the oven. Because the metal sheet cookies baked faster, they gave up most of the moisture of the dough and had a lower thermal mass than the less cooked (more gooey) cookies on the stoneware sheet. Your measurement device might indicate a higher internal temperature of the lesser cooked (gooey dough) because of the higher thermal mass of the uncooked dough. The metal sheet cooked the cookie faster. The stoneware thermal mass absorbed more of the heat during the same time, and were under-baked. The apparent higher measured temperature of the lesser cooked stoneware cookies is a thermal measurement error. What kind of thermometer was used, by the way?

Rick Marz

[deleted-71487]

An interesting sub-experiment suggests itself from rmarz's hypothesis: test with different kinds of thermometers and measurement techniques and see if it makes a difference.

Don't forget that heat is leaving the cookies as soon as you remove them from the oven. The unfinished cookies contain water, which has a massively high ability to absorb heat as it evaporates, but also a very high thermal mass. These make it very hard to get a good measurement, and it's very hard to predict which way the experiment would come out. Measuring the temperature while still in the oven would be one way to alleviate this problem (e.g. with a probe thermometer, which can be had very cheaply at a hardware store, usually). Infrared thermometers are more expensive, but probably you could borrow one if that's a problem.

[Terri1]

The thermometer we used was just an inexpensive digital food thermometer from the grocery store. We tried the test of taking the temperature while the cookies were still in the oven, it was a little difficult to do, my hand got very hot! The temperatures seemed to be similar this way.

I would like to understand better the term: thermal mass. We have looked up the definition, but we would appreciate any additional explanation you could provide as it pertains to this experiment. Thanks!

[rmarz]

Terri1 - Thermal mass refers to the ability of a material to contain heat. Some materials have low thermal mass and will show a large change in temperature with very little caloric energy change. They usually possess low density (styrofoam, most plastics or dry wood would be an good examples). They don't conduct heat well and we think of them more like insulators. On the other end of the spectrum you would have a more dense material, metal, bleep with a high water content, concrete or other materials that will contain and store a large amount of thermal energy without a significant increase or decrease in temperature as calories are added or withdrawn. They also conduct heat much more quickly.

Have you ever wondered why some vegetables on your plate seem to get cold very quickly while others stay hot, even though they both left the oven at the same time and temperature. Thermal mass! Hope this simple explanation helps.

In my prior reply, I suggested that the less baked (gooey) cookie still had significant water content, therefore higher thermal mass than the drier, fully baked cookie (lower thermal mass) and the act of placing a metal thermometer tip into the fully baked cookie had the effect of lowering the temperature much more than the thermometer in the heavier, gooier, more moist dough.

Rick Marz

[Terri1]

Thanks for the helpful information!