Monday, August 10, 2009

Food Science: Should Bread Dough Be Kneaded Twice?

Something I've wanted to do on this blog for a while, since I have a scientific background, is "food science." I like to find things out for myself when I can, and I think people find it interesting to read about these kinds of experiments. Since my sourdough starter is rip-roaring these days, I'm making a lot of bread, and so the first installment of what I'm calling "Food Science" is an investigation using bread.

I've been reading a lot about bread making lately, as would make sense, and one thing I've noted in a few cookbooks is that most recommend directly against a second kneading phase (which I still like very much for flatbreads because of the chewy texture it seems to impart). I almost always knead the dough again after I punch it down, but yesterday I decided to do some science. I made the dough as usual, just a normal sourdough recipe, and then after the first rise, I cut the dough into two pieces, as equal in size as I could manage. One of those pieces was kneaded a second time for approximately ten minutes, and the other was carefully and delicately shaped into a baguette without a second knead, trying to preserve much of the volume from the first rise. Here's the two loaves just after shaping, the re-kneaded loaf in front:
two sourdough baguette loaves before the second riseAs you can see (if you look carefully), the dough in the rear is slightly larger than the loaf in the front because of the gas bubbles that have been retained by not kneading it a second time.

There are two competing ideas, both entrenched in the art and science of bread making that lead me to have curiosity about which will be a more effective approach. First of all, more air is more air, and it should lead to more volume in the loaf that wasn't kneaded a second time. Furthermore, there should be less-developed gluten in that loaf, so hopefully it will even be able to rise further on the second rise, getting some of that bubbly texture that is typical of sourdough loaves. On the other hand, re-kneading the dough should redistribute the ingredients, though it pops many of the air bubbles, giving the yeast a better chance at finding the food it needs to grow during the second rise. It should also help stretch the gluten and develop it further, perhaps facilitating the second rise even more (since the dough will be relaxing while it rises that second time). What's going to happen?

An hour later, I took another picture, but it doesn't tell the whole story. For the first half an hour of the second rise, the loaf that was not re-kneaded was clearly larger than the loaf that was. By the time I took the picture, after an hour (when the re-kneaded loaf had approximately doubled in volume), the loaf that I had merely shaped (and didn't re-knead) seemed to be smaller and had a surface appearance not unlike stretch marks, as if it had stretched and then shrunken back. Perhaps its second rise went on too long. Perhaps the redistribution of the ingredients really was important. I'm not sure. Here's the result after the second rise, though, with the re-kneaded loaf in front:
two sourdough baguettes after the second riseObserve that the loaf in front, which was re-kneaded, appears smoother and is legitimately slightly larger than the loaf in back, which was not re-kneaded.

After scoring them as identically as I could using diagonal marks, I baked the loaves. The oven-spring of the re-kneaded loaf was also noticeably larger than that of the shaped loaf. Hmm.... Twenty-five minutes in a 400 F oven gave me this:
two sourdough baguettes freshly out of the ovenThe loaf in front, the re-kneaded loaf, is obviously bigger and better-looking. So much for the idea that more preserved gas means a more voluminous loaf....

The real question lies in what they look like inside, though. See for yourself (nearly identical):
two sourdough baguettes freshly baked and cut although they didn't seem to rise enoughThe loaves are oriented as before, but it doesn't really matter since they're pretty well identical inside: no big bubbles in either, just a pleasant, smooth, bread-like texture.

So... in a side-by-side comparison, the results of this experiment (re-kneading versus not re-kneading) are:
Taste: Identical (sourdough-bread-like).
Texture: Essentially identical (pleasantly springy with a nice mouth feel).
Density: The re-kneaded loaf is slightly lighter than the not-re-kneaded loaf.

The jury is out, then, because the body of literature on "don't re-knead the dough" is pretty extensive and yet this small experiment (that wasn't performed under ideal conditions) seems to suggest otherwise. The main result of this experiment: two yummy loaves of bread that I get to eat simultaneously in alternating fashion! Win-win? I think so.

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Hot relax said...

Very useful tips

+^! said...

Very good experiment, I've been trying to find out if rekneading the dough will actually degas it. Now I know it's safe to reknead dough, probably better for it too!