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In this sourdough recipe, it suggests basting the bread with a cornstarch slurry. I would assume this is meant to promote crust development, but how does that work? I usually see such a slurry used to thicken liquids.

Other recipes that use this method:

It appears to be a presentation thing (makes it look "professional") and possibly a Jewish tradition.

Edit: Do note that the question is "Why cornstarch? How does that work?". I understand the desire for a good crust, and I understand that the slurry is meant to promote crust development, but I fail to understand what it is about cornstarch that mimics good crust development.

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I can honestly say I've never heard of that before. – rfusca Feb 23 '12 at 21:26
@rfusca It's the weirdest thing I've come across, that's for sure. – Yamikuronue Feb 23 '12 at 21:34… amused me while searching for links: it appears to be talking about this technique, then some bot or something comes along and posts an answer about thickening sauces – Yamikuronue Feb 23 '12 at 21:40
I have used this slurry and it makes an amazing shiny crusty bread...first used this nearly 25 years ago and still use it – user34583 Mar 30 '15 at 15:30
up vote 3 down vote accepted

I've seen bread recipes like the one that you described.

When bread is baked in an oven with steam- the starch in the crust is able to gelatinize before it all dries out and becomes crispy. This is what makes the crust crisp, shiny, and delicious- characteristic of "artisan" breads.

Most people don't have steam enhanced ovens (or the ability to hack their oven to add steam: How can I create steam in a normal oven to promote bread oven spring?)

The recipe you linked has water added for steam but then takes out extra insurance (they cheat) by adding the cornstarch glaze to mimic the effect. By adding extra, pure, starch on the surface of the loaf more gelatinization occurs. Additionally, cornstarch gelatinizes at a lower temperature that wheat starch. Conceivably, you should be able to use any starch and see similar results but, in the US at least, cornstarch is by far the most common.

It shouldn't be necessary if you are able to produce enough steam in your oven.

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Cornstarch slurries are used because they make the crust of the bread shine. This happens because Cornstarch mixes are translucent; whereas flour mixes are opaque.

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Why cornstarch and not plain water, then? Water is translucent. – Yamikuronue Apr 9 '12 at 16:11

Creating a cornstarch slurry with a ratio of 1/2 cup cold water to 1 teaspoon cornstarch and then heating it to a gentle boil before brushing it on the bread will create a shiny golden brown crust.

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Ok, but why? How? What does the cornstarch do? You've basically just repeated the instruction over again >.> – Yamikuronue Feb 24 '12 at 15:17

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