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I'm used to the crust on sourdough bread being thick and chewy, but had always attributed that to the longer rise, and baking with steam, that one normally does with sourdough. However, this week I made a hybrid sourdough* in my bread machine, and its crust was thicker, browner, and chewier than non-sourdough breads made in the same machine. Since the baking cycle and atmosphere are the exact same as, say, last week's whole wheat loaf, it's not how it was baked.

So my question is: what is the physical or chemical property of sourdough starters that results in a heavier crust?

Note that while there are a number of questions on the board about sourdough crusts, all of them focus on manipulating the baking environment, and not on properties of the dough itself.

(* hybrid sourdough: some sourdough starter plus a little commercial yeast)

  • I think it's possible the effect has something to do with the bread machine and how it mixes the sourdough. I.e. it's not just a property of the starter in itself. – Mark Wildon Feb 8 at 15:37
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    The bread machine mixes sourdough the same way it mixes every other dough. There's no "sourdough" setting. – FuzzyChef Feb 8 at 19:11
  • Fair enough. But sourdough is often higher hydration than normal dough and this will affect the bread machine's action. Are you comparing doughs with the same hydration? – Mark Wildon Feb 10 at 11:43
  • Don't know, wanna try that out as an answer? – FuzzyChef Feb 11 at 1:03
  • I've personally never noticed your experience of sourdough breads as being particularly crusty compared to non-sourdough versions. That's not to say there isn't a difference, but I'd imagine dough composition in general is a significant factor. Hence my question: was your sourdough dough in the bread machine exactly the same composition in terms of other ingredients/proportions to your comparison non-sourdough bread in the bread machine (aside from leavener)? Because a whole wheat loaf (maybe even with other ingredients) will not have the same crust as a lean-dough white sourdough. – Athanasius Mar 2 at 19:43
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Here's a scientific breakdown:

Sourdough starter is the primary leavening agent in any sourdough, including your hybrid here. Technically, it's just water and flour. The flour already has all the yeasts and bacterial spores it needs to ferment, and the water activates the fermentation process via an enzyme called amylase.

The amylase breaks down the starch in the flour into sugars, which the yeast will metabolize, producing carbon dioxide gas. Anything in the sugars that the yeast can't eat will be fermented over time by the bacteria, producing more amylase and breaking down the sugars further so that the yeast can eat it. The bacteria creates lactic acid as a byproduct of this process, giving sourdough its unique "sour" flavor.

However, the same process that breaks down the sugars in sourdough starter can also break down the proteins in the dough. This gives you weaker gluten - or, a denser, chewier bread than what you'd obtain with only baker's yeast. On top of that, your bread is a hybrid, which means there's even more yeast in it than usual and even more leavening. More leavening, more enzyme production by the bacteria, more potential for protein breakdown.

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    So, you do realize that with your last comment, you made it impossible for me to select your answer, yes? – FuzzyChef Apr 11 at 21:53
  • I removed it. Sorry! – harmothic Apr 11 at 21:55
  • So why does the breakdown of proteins make the bread chewier? I'd think it would be the opposite -- baked goods made with low-protein flour are generally speaking tender and soft. – FuzzyChef Apr 11 at 22:09

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