How gluten affects bread texture in a 90% hydrated dough

Final Project to Edx Harvard Science and cooking course by Michelle Cailleaux

Abstract

My project consists in experimenting if differents concentration of gluten affects Breads texture. I took one spanish bread recipe called Pan de Cristal and maked many variations in the flour gluten concentration by adding gluten to all purpose flour and not changing the quantity of the others ingredients. I checked the differences in the viscosity of the dough and the final elasticity of the bread and compared them. I found out that differences in flour gluten concentration affects breads texture, it changes the capacity of the dough to absorve water leading to differents crumbs, crusts and elasticitys. That can be usefull to make different breads with the same ingredients. 

[ Left picture: Final bread result ]

Motivation of experiments

I decided to study bread because i think it is simple and complex at the same time. Simple because it needs just 2 ingredients to be done: flour (starch and gluten) and water. Complex because changes in gluten, starch and water concentration or even changing the way of mixing these to ingredients can lead us to total differets results. Like many others i did bread sometimes, some worked, some didnt, and I want to understand why. 

Wheat flour basically content starch and gluten proteins. These proteins in contact with water unfolds and stick to each other, forming a elastic network that attraps the starch, other bread ingredients and gas produced in fermentation and baking. Time is necessary to gluten hydrate and develop the network, so as work, by kneading the dough.

From the scientific perspective I think its very interesting investigating how those gluten networks affects the doughs viscosity and elasticity, that is closely related with the capacity of the bread to grow (retaining CO2 produced by the yeast on the fermentation and steam by the evaporation of water on the oven), and how it is reflected in the final elasticity of the bread that is percepted as different texture.

Materials and Methods

I did a lot of doughs, in different days, using the same ingredients just changing the proportion of gluten on the all purpose flour. The doughs were kneaded with the same stand mixer, rested and were baked the same way, for the same time. After the doughs were kneaded I measured the time they took to fell from a glass to compare their relative viscosity. After the breads were cooled I used force-displacement measurements with a 550 g weight to determine their elastic modulus with the formula: E=(F/A)/(ΔL/L0) and calculated the crosslinkdistances between their bonds by E=U/l^3.

Material to make the dough: Stand Mixer, Scale, Bowls, spoon, Oven, Tray; to measure vicosity: Timer, glass cup and to measure Elasticity: Scale, 550gWeight, Ruler. 

Ingredients for the Bread: Flour, Gluten, Water, Yeast, Oil, Salt. How to prepare the bread: Mix flour, gluten and salt. Dissolve yeast in 2/3 of the water and add oil. Mix both liquid and solids and knead it in the stand mixer with the hook for 5 minutes in low speed. Add the remaining water very slow (almost drop by drop) while kneading in fast speed until all the water is totaly incorporated. Let the dough rest in a flour bowl for 1h, fold it, let it rest 1 more hour, shape the bread and let it rest the last hour. Bake it at 250C for 10 minutes and more 45 min at 200C. Let the bread cool in a tray. 
[Picture of measuring relative viscosity of one of the doughs]

Results and Discussion

The experiment was made by making and comparing breads with different percent of gluten on the flour content. The original recipe is a spanish bread that calls for 45% water and 50% bread flour with 15% gluten. In this recipe the flour is 90% hydrated, wich is not usual. The range of hydratation normaly is between 60% to 80%. For this reason the flour needs even more gluten. The amount of gluten was gradually changed from 10% to 28% percent on flour weight, the others ingredients were the same.
[ Right picture: 20% gluten flour dough ]

The first differences appreciated while kneading and forming the doughs were the time they took to knead and their viscosity: The doughs with more gluten took more time to knead and became more viscous. 10% to 14% gluten wasnt able to knead, 14,5% to 20% took 10 to 15 minutes to knead, and 23% to 28% 20 to 40 minutes. Their relative viscosity amost double every 5% gluten was increased in flour (20% gluten flour was double than 15%, that was double than 10%). 

[ Right picture: 10% gluten flour dough ]

While folding and shaping the differences in gluten percent were also noticed, the less gluten percent were more difficult to manipulate and shape.  After resting and folding for 2h (wich increases the dough viscosity) almost every dough was able to hold a form, except less than 14% glutent content doughs.
[ Left picture: doughs with 10, 15, 20 and 25 percent of gluten on flour weight ]




 In fermentation and baking differences in shape were noticed: The highers glutten percent doughs seemed to rise up and the lowers rised to the sides (left and righ). After backed, the breads looked almost the same but the textures were differents. The elasticity of the breads seemed to be directly related with the amount of gluten used. The more gluten had the dough, the more elastic was the crumb, and the more chewe was the crust of the bread. Their elasticity increases almost in a linear way from from 9.000 (15% gluten flour) to 23.000 Pascals (28%). The viscosity of the doughs showed no affect in the final size but in the shape of the breads, the more viscous was the dough, the more rounded was the bread. The less viscous were flater.
[ Right picture: top bread 20% gluten on flour weight, middle 17%, bottom 15% ]

The elasticity of gluten networks are crucial to make wheat flour bread with high hydratation. For this recipe, a flour with lesse than 14,5% gluten does not work properly because does not form networks capable to hold the air in the fermentation and baking, so the bread do not rise. The amount of 15% to 17% gluten on flour is a very good choice, they are difficult to shape but make a spetacular bread, with crunchy crust and nice crumb. Flours with more than 20% gluten percent take to much time to knead properly with a stand mixer.

[ Final Project Result, but until not Pan de Cristal ] 

Conclusion and Future Directions

To conclude, I found out that differents percentage of gluten in flour make quite differences in bread texture but not less important is the correct kneading of the dough. As we´ve learned, the gluten form networks while the dough is knead and that contributes to the viscosity of the dough, the more gluten the more viscous. However, if not knead properly, even with a high gluten percent, the dough doesn´t get viscous enough to hold the air bubles and the bread do not rise correctly, which increases even more its elasticity.
As I was making this project I found out that high hydrated doughs were very difficult to handle. They seemed to be difficult to knead in a stand mixer (by hand it´s impossible), so I´ve tried anothers ways to form doughs different as kneading. The next step in my investigation is studying differents ways to form this type of doughs. 

Extra

So I did more experiments after ending my project. I discovered that I could work very well the dough with a hand blender. Sounds wird doesn´t? You can see a youtube video on this link. And I decided to let the bread ferment trough the night and I end up with perfect crunchy ever cristal bread. =)

Cristal Bread finally achieved on the picture below