Using thermometers to test for bread doneness
This post will be a little long; sorry, but I want to be thorough.
Several years ago, I was teaching baking classes at the Japan Institute of Baking (JIB) in Tokyo. A big part of the Institute is devoted to research on all manner of bread topics. An engineer there gave me a gift--a small probe that had a USB port on one end and a sheath to cover it. It is used to track the temperature changes within a loaf of bread. I asked him when bread reached its maximum internal temperature, and he said it was attained when the bread was approximate two-thirds through the bake. Hmmm. When I returned to Vermont, I put the probe into my desk at King Arthur and other activities took my attention--I didn't test it.
A year or so later, I was in Nantes, in France, visiting with dear friend Hubert Chiron, one of France's most important bakers, writers, and researchers. We were at INRA (Institut National de la Recherche Agrinomique), where he works. I asked--"Hubert, when does bread reach its maximum internal temperature?" "About two-thirds through the bake," he replied (I had not told him about the Japanese conversation). Hmmmm.
When I returned from that trip, I pulled out the probe and did the experiment for myself. Here's how it works: You take the sheaf off the end, plug the USB port into a computer and start the program. On the computer screen you see a grid that graphs temperature change on one axis and time on the other. Then you remove the probe, put the sheaf on, and wrap the whole thing in the center of a loaf of bread. It stays there throughout the final rise and the entire bake. Once the bread is baked, out comes the probe. On the computer you can see that there was no increase in temperature for a long while, since the bread was initially rising at room temperature. Eventually it curves upward after it has been loaded, and the temperature begins to increase. Sure enough, the temperature rises pretty quickly and then begins to taper off. Eventually--about two-thirds through the bake--it pretty much flatlines and temperature increase is minimal.
Not too long after that, I was teaching a five-day class at King Arthur, and one of the students wanted to test doneness of a loaf using a thermometer. I told the class about my experiences in Tokyo and France, and my own recent experiment. Two things happened: one was that one of the students was a writer for Cooks Illustrated. His ears perked up, and a month or so later he sent me a one-page article he had written for Cooks; basically he had replicated the experiment I had done, with the same results. The second thing was that another student in the class just happened to have, in his glove compartment, a rather sophisticated temperature probe. He went and got it, and we inserted it into a loaf of ciabatta that was about to be loaded. Being a bunch of dweeby bakers, all of us just stood around, riveted to the display that showed the temperature rise. When the bread hit 210F internally, out it came. It was half done at most. I wouldn't go near it, but I offered a slice to anyone who wanted one. No takers. Believe me, if you were blindfolded and squeezed that loaf and a roll of Charmin, you wouldn't know which one was bread and which was toilet paper.
I know that there are plenty of people who have their own opinions and practices that are different from mine, and that is totally fine. I started out working with French and German bakers, and squeezing and thumping were the ways that doneness was ascertained (along with the length of time the bread was in the oven and its color). It really is foolproof once the skill is acquired. One might also say it is more respectful to the bread, since there are no small holes in the bottom where a thermometer was plunged. And it sure feels good on the hands.