My bread looks great when I just took them out from the oven. But right after cooling a little, the surface of the bread starts wrinkling. Why?
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Sounds like the heat from the interior of the bread is essentially steaming the crust, which the softens and deflates - a result of the loaf being slightly undercooked. Don't be afraid of getting some color on the top of your loaf; many experts suggest baking until it's dark brown on top for maximum flavor. If that's just not for you, though, try leaving your loaf in the oven with the door slightly cracked for awhile after you turn the heat off.
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Baking bread to a deep golden brown is also referred to as "putting a French bake on it." Americans are sadly known for sometimes preferring pale, anemic breads and pastries. You can even take its temperature. Traditional loaf breads should reach an internal temp of 185; baguettes and sourdoughs should go to 210. Get your bread out of the oven as soon as it is done, and most importantly, get it out of the loaf pan. The longer it sits in the pan, the longer it steams itself wrinkly. Turn or lift it out of the pan and set in on a cooling rack as soon as it emerges from the oven.