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Hi!

I'm fairly new to sourdough and just bought an oval banneton. 

I've baked great loaves but it seems that most time they crack a bit outside of the score which I feel Ike is preventing a greater rise. Here's a picture of my last 50-50 while wheat sourdough following the perfect loaf recipe.

What do you think this is due to? 

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. 

Jeffrey

The motive force for oven spring is often stated to be the expansion of gas cells in the dough, combined with a burst of activity by the dying yeast. However, this is only a part of the story. Gas expansion is unlikely to be sufficient by itself because the expansion of gas from a room temperature of 25° C to 80° C is only about 20%. And a burst of activity from the yeast is likely to be small because gas production declines at temperatures above 40° C. The other important drivers are given by scientific text books as the release of dissolved carbon dioxide as the temperature rises, combined with the boiling off of ethanol, which is also mixed with the water. For example, in “Baking Science and Technology”, Pyler quotes the following approximate contributions, which I have rounded to whole percents:
Ethanol boiling: 50%
Expansion of existing carbon dioxide gas: 29%
Carbon dioxide from solution: 19%
Yeast activity: 2%

That leads to the interesting question of how the carbon dioxide and ethanol come to be dissolved in the water. The answer presumably is that they are already in solution when they are created by the yeast, and remain that way until the loaf is baked. The likely time when this could happen is during the initial, apparently quiescent, part of bulk fermentation before the dough starts to rise. If this is true, the yeast is actively producing carbon dioxide early on, but the gas is not immediately visible because it remains in solution. Eventually, however, the solution becomes saturated and any further carbon dioxide has to be released as gas, causing the dough to start rising.

To explore this idea I conducted an experiment in which I divided a batch of dough into portions and baked them after different lengths of bulk fermentation. I started by mixing 500g of all-purpose flour, 350g of water, and 10g of salt in a food processor for 30 seconds. I removed 100g of the mixture as a control sample, coated it in rice flour to reduce sticking and placed it in a 250ml pyrex beaker. I then added 1.5g of active dried yeast dissolved in 5g of water to the food processor and mixed for 5 more seconds to incorporate the yeast. Then I cut 7 samples from the dough, each weighing 100g. I coated each sample with rice flour and put it in a 250ml pyrex beaker, covered loosely with foil. I immediately put the control sample and the first yeasted sample into a 450°  F oven to bake for 20 minutes. The remaining 6 samples were baked at half hour intervals over the next 3 hours.

The picture shows the beakers after baking, lined up in order of fermentation time, with the control sample on the left. The graph below shows the heights before and after baking. The baked height increases steadily for 2 hours, when it reaches a plateau at about twice the unbaked height.

The lower graph shows that the dough height before baking remains unchanged at first, only beginning to increase at 2.5 hours, even though the baked height increases steadily right from the start, consistent with the idea that carbon dioxide and ethanol are present but mostly remain in solution in the dough.

There is no sign of a step increase in baked height which would have been produced by a yeast burst. Indeed, extrapolating back from later samples, the rise in the sample baked immediately corresponds to only about 10 minutes of fermentation at room temperature.

The plateau in baked height after 2 hours most likely indicates a limit to the capacity of this dough for oven spring, since the rise in the unbaked dough after 2 hours indicates that fermentation continues. It would be interesting to run a similar experiment with different kinds of dough handling to see their effect on oven spring.

This experiment demonstrates that the yeast is active right from the beginning of bulk fermentation, even though there is little outward sign. It also shows that oven spring does not require that the dough has risen substantially. By the time that a noticeable rise indicates the end of bulk fermentation, the dough is already loaded with enough carbon dioxide and ethanol to drive a substantial oven spring.