Thursday, February 18, 2016

The Science Behind... scalded flour

After accidentally using hot water instead of warm water during the autolyse period of Preston Yancey's white bread, I was surprised to learn that intentionally scalding the flour is a technique used in Japan for super-soft bread.

I wanted to learn more.  Why does scalding the flour lead to soft bread?

In this post, I will answer the following questions:

1. What is an autolyse?
2. Why would you add boiling hot water?  Why can't you do this for regular bread recipes?
3. What is starch gelatinization?
4. What is tangzhong?
5. How can I use scalded flour in my bread baking?

1. First off, what is an autolyse?  It's a technique used by some bakers to boost the gluten formation in their bread. By mixing water and flour before adding any other ingredients, you allow the protein to absorb all the water without having to share it with the starch and without being stressed by the carbon dioxide bubbles from the yeast pushing against the gluten net before it's had a chance to firm up.  After an autolyse of just a few minutes, the gluten is very well formed and is ready to stretch with the expansion of yeast bubbles.  Salt and yeast are added after the autolyse period is completed.

2. What makes scalded bread different from the autolyse?  Why would you add boiling hot water to flour?  With an autolyse, you add warm water.  This is because protein can absorb more warm water than cold water. The autolyse is purely to develop the gluten.

Scalding flour with boiling water, in contrast, activates another chemical reaction entirely-- starch gelatinization.  Instead of being absorbed by the protein, the hot water is absorbed into the starch molecules.  That leaves the gliadin and glutenin (the proteins in flour responsible for creating gluten) bereft of the water they need for strong gluten formation.

Bread with high gluten formation tastes chewy.   This is why you don't want to overmix doughs like muffins and cakes- they can become rubbery.  By taking water away from the gluten and jump-starting starch gelatinization instead, you create a dough that is super soft.

Why can't you do this for regular bread recipes? Simply put, you cannot substitute hot water for the usual warm water because it kills the yeast.  That is why it really only works when you add hot water to the flour and let it cool before adding the yeast and salt.

3. What is starch gelatinization? As you may recall from my The Science Behind... series on the baking process, starch gelatinization occurs in the high heat of the oven.  This graphic might clarify things:

Here is what happens when dough is in the oven.  First, the yeast go crazy and produce lots of bubbles before the heat is too high and they die off.

Next, the gluten strands release water to solidify around the carbon dioxide bubbles created by the yeast.

With all the free water suddenly available (released by the gluten), the starches absorb it until they can't absorb any more; they then burst, releasing the water and sugars in a process called gelatinization.

So instead of waiting for starch gelatinization to occur in the oven, scalded flour introduces it much sooner in the bread baking process.

But what exactly IS it?  This article explains it best:
This formation of gummy networks gives polysaccharides (heated starches) the ability to replace eggs in many baked goods with relative success. The tangled networks can entrap water and other molecules in the batter, locking in moisture and keeping ingredients evenly dispersed. Polysaccharides also interrupt the springy gluten networks formed by flour to create a more tender, delicate texture often desired in muffins and quick breads. And just as a network of egg proteins can hold things together, polysaccharide gels help keep baked goods from falling apart. Who would have thought that such different molecules could function so similarly in the kitchen!

Here's a graphic.  As you can see, the starch molecules absorb water under heat until they burst, forming a tight net of gel.

Here is the problem, one that I ran into and one that has been solved by the Japanese technique of tangzhong (more on that below): you don't want to scald the entire flour content of your dough.

You do still want some gluten in your dough to help with structure.  This is where tangzhong comes in.  It can be understood as something of a roux.  Like a roux you might use in a gumbo, adding just a little bit of scalded flour will help soften your dough, while maintaining the gluten structure.

4. What is tangzhong?  Tangzhong is a technique I learned about recently.  According to this post,
 The Tangzhong roux technique was developed in Asia around 2000. The technique was first mentioned by Yvonne Chen in her book, “Bread Doctor”, published in Taiwan in about 2003. Tangzhong means "soup" in Chinese.  
A Tangzhong Roux (also called a Tangzhong Water Roux or Water Roux) is a flour and water roux that is added to yeast bread recipes. This is done in order to make a loaf of bread that is lighter, has a more tender crumb and a longer shelf life.

The flour and water are mixed and heated to 149-F (65C). This gelatinizes the flour and forms an unflavored translucent pudding-like roux.

If you plan to use a water roux in a regular recipe such as my 2-3 white bread, use only about 5% of the total flour weight to calculate your roux flour weight.  The flour in a water roux absorbs 5x the flour weight in water.

So if you are planning on making a dough with 375g of flour, your roux should be about 19g of roux flour (375 * .05) and 95g of roux water (19 * 5).  The post on Chowhound suggests just adding it to your recipe without doing any recalculations for hydration.

Just add your paste to the amount of water you would regularly use (in the case of my 2-3 dough, 250g of water) and then, when it is lukewarm, adding it to the normal 375g of flour. 
5. How can I use scalded flour in my bread?  Besides the Japanese soft breads, I learned that scalded flour is a technique practiced in Scandinavia as well.  Virtuous Bread has some tips for using scalded flour (in sources below).  I learned through my research that scalded flour is most often used in non-wheat doughs like ryes, which have very little gluten content and do not hold their structure well.  By scalding the flour, bakers can achieve a soft dough that has a cake-like consistency, less bitter flavor, and holds together without the help of gluten.

For a rye bread recipe with scalded flour, check out this post:  rye bread with scalded flour.

I hope you enjoyed this tutorial on scalded flour and starch gelatinization.  It's something I was unfamiliar with, but I'm thinking it could be a great way to add softness to breads without fats like eggs or milk.

Have you ever used scalded flour or a water roux in baking?  Let me know in the comments!


Sourdough Library

Science and Food

Virtuous Bread

Chowhound Tangzhong Roux FAQ


Sean Nel said...

This is very interesting and makes for a fascinating read. Thank you!

I have used scalded rye flour before in Danish bread recipes and have always been curious about the effect that warm to hot water has on baking especially as a hot water pastry dough is one of my favorites. I wondered how I could apply this to my bread baking and so did a simple experiment with an overnight autolyse using very warm (not hot) water.

The results are extremely encouraging and I'm still building up quantitative data, but needless to say that the bread is truly special.

Thanks for helping to confirm my suspicions! I can now continue forward armed with this new knowledge...


Unknown said...

Thanks for the info! I recently found a recipe book online from 1894, "The Journal of Agriculture Cook Book" ST LOUIS, MO JOURNAL OF AGRICULTURE, CO... It is full of wonderful bread recipes that our great-great-great grandmothers would have used, and almost every yeast bread recipe calls for "scalding" the flour the night before, many of the cooks contributing recipes were from Britain, Scotland and Ireland...If you google I'm sure you can find this book too.. very interesting! I liked it well enough that I printed out the whole thing!

Christine said...

Thank you for the scientific explanation! I have been making soft bread by "gelatinizing" a small portion of water/flour in the microwave for years. Then I ran into the term "autolyse" in bread making. In my mind, I did not think there was that much of a difference, but I understand now one form is hydrating, while the other is creating gelatinization.

Let's go to Heaven said...
This comment has been removed by the author.
Kyle said...

Funny, it was a complete accident (or maybe just carelessness) that I used scalding hot water, too. Here's my little secret recipe for awesome rolls er...well...I haven't found the proper name for them yet. They are like little flat bread rolls, almost like pita but with a more crunchier outside. Anyway, I mixed plain water and flour with a little salt and sugar, until the consistency was way too dry to mix by hand, so I heated up some scalding hot water, which was added to the mixture, it became too runny, so I added more flour, a touch of baking powder and baking soda and yeast, and mixed until the consistency was tacky..not sticky and not not sticky. I let it sit and rise for about 1 hr, then I tore it until little pieces and just threw them on the oven rack. Yes, I'm a lazy guy, I just tend to throw my dough on the rack and hope for miracles. Well, turns out it was the best pita roll thing I ever made. They say some of the best recipes were made by accident. and that's what we did. Thanks for the post explaining all of the science. I hope you guys can enjoy my recipe.

Debby Riddle said...

This is wonderful information. Thank you so much!

Kyle said...

Debbie, thanks for your post because I got an email saying someone has replied to this topic. Welll, I'm Kyle and I posted my recipe above and I lost it to time and now I have it again. Thank you so so much and I hope you try it, it's really the best. xo

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Unknown said...

Hi, is it possible to autolyse overnite with tangzhong combined,so theres no need to knead anymore the next day ?

teeny-weeny said...

This is SO HELPFUL! It always leaves me mind-boggled when recipes tell me to do something in a specific way and doesn't explain WHY. I think it helps a lot to understand why we do things certain way so I can apply it in other cookings or just know what I'm doing. This article answered a question that's been bugging me: I wanted to know why some tortilla recipes ask for warm water while some ask for hot water. Thank you so much for explaining the science behind these processes!

M said...

Amazing!!! Answered all my questions in the language I understand!

Marion said...

Thanks so much for this information.
So I'm wondering, in theory there's nothing preventing me from using both techniques, as in adding Tangzhong and yeast to autolised flour ? and if so, would I add the Tangzhong to the water and flour mix, or later with the yeast ?

adiban said...

An awesome read .. i used hot water to make Indian roti , they turn out extremely soft .. but just a question can the gelatinization create any health problems?

Unknown said...

I've never tried this with bread but it's common practice with the dough used for what are commonly known as "potstickers". It makes the dough more manageable and forgiving. I'm going to have to try this with perhaps a rye bread, something with which I've never had any luck. Maybe other non-wheat breads as well. Thanks.

Marco da Vinha said...

A traditional Portuguese corn bread requires the scalding of corn flour.

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Audi Nugraha said...

Pure GOLD information, thank you for sharing :)

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