Posted in baking, dry heat

Hydration Levels in Bread: An Exploratory Study

Introduction

As is widely noted in the literature, the hydration level of a dough affects several properties of the resulting bread, most notably hole size. However, preferred hydration levels for certain types of bread are not agreed upon with much precision. One reason for this uncertainty in the field is that hydration level affects different flours differently (see for instance http://www.artisanbreadinfive.com/2008/02/10/qa-flour-and-water). Having recently been burned by this imprecision, the author undertook the following study to offer concrete data on the affects of a variety of hydration levels on King Arthur Unbleached Bread Flour.

Method

This study manipulated one factor, water content, which was measured in baker’s percentage, the ratio of the ingredient (water) to flour, by weight. The factor had four levels: 60%, 70%, 80%, and 90%.

The water was brought to 100F and mixed with 3/4 tsp (approximately 1 baker’s percent) of active dry yeast in a non-metal bowl. This mixture was left for 10 minutes to allow the yeast to become active. Then 200g of flour was mixed in until none of it was dry, to the extent that this was possible. The 60% dough was unable to incorporate all of the flour with the mixing method utilized; this was likely due to experimenter error as even drier doughs have been recorded in the literature. The results of this step are shown in Figure 1. All doughs had an internal temperature upon mixing of approximately 75F in a 62F room.

mix_collage
Figure 1. Doughs upon mixing. From upper right, clockwise: 60%, 70%, 80%, 90%.

The resulting mixture was left to autolyze for approximately 20 minutes. During this time, the flour absorbs water, which then allows enzymes in the flour to break down some of the starches into sugars. The yeast feed on these sugars and multiply before the addition of the salt, which limits their growth. The absorption of water by the flour also makes the dough feel drier, which is helpful for working with higher hydration doughs. After this pause, 3/4 tsp (approximately 2 baker’s percent) was incorporated into the dough. The results of this step are shown in Figure 2.

autolysis
Figure 2. The doughs after autolysis. Clockwise from upper left: 80%, 60%, 90%, 70%.

The dough was then left to ferment for 2-3 hours, until doubled in size. Approximately every half hour, the dough was stretched and folded as described in Robertson and Wolfinger (2010).

An exception was made to this method for the 60% dough, which would be less likely than the others to develop and organize its gluten in the later stages (as the method used here was developed for higher hydration doughs). It was kneaded for a few minutes, short of fully developing the gluten. In contrast, the 80% and 90% doughs developed gluten to the point of showing translucent windows with only these occasional folds.

gluten_windows
Figure 3. Translucent “windows” show effective gluten development in the 80% and 90% doughs. These took little to no effort to stretch (the 80% one was created by accident when a the dough stuck to the author’s finger) and no kneading.

When doubled, the dough was preshaped into a boule, with focus on creating some surface tension on the top of the boule. During all steps, the dough was covered with plastic wrap, but from preshaping on a layer of olive oil was added between the dough and the plastic wrap to prevent rupture of this top layer upon removal of the covering.

The dough was then rested for 30 minutes and shaped again. This began the phase of proofing, which varied in time. When available, the proofing dough was inverted into a floured banneton to support the boule’s shape. Proofing was considered to be finished when the dough slowly recovered from being poked; unfortunately, successful proofing did not guarantee an available oven and the 90% dough may have been overproofed while waiting for space.

When ready to bake, the oven, containing a tagine, was preheated to 500F. The dough was inverted again into the tagine, scored in a square pattern with a lame, and put into the oven covered with the tagine lid. The oven temperature was reduced to 450F (see for example Lahey, 2009) and the bread was baked for 20 minutes. Then the cover was removed but left in the oven to remain preheated for following bakes (see Appendix A), and the bread was baked uncovered for an additional 20 minutes. An exception to this was the 60% bread, which was done after the first 20 minutes and removed. All loaves were cooked to an internal temperature of at least 210F.

The loaf was then removed from the oven and left to cool completely on a wire rack.

Results

We present here the raw, baked data.

60percentprofile
Crust of 60% dough.
60percentcrumb
Crumb of 60% dough.
70percent_profile
Crust of 70% dough.
70percentcrumb
Crumb of 70% dough.
70percentprofile
Crust of 80% dough.
80percentcrumb
Crumb of 80% dough, complete with actual crumbs.
90percentprofile
Crust of 90% dough.
90percentcrumb
Crumb of 90% dough.

Figure 4 shows the relative size of the loaves in ascending order of hydration. Figure 5 gives a bar chart of hydration level by loaf height. As predicted, higher hydration correlated with larger loaves containing larger holes and thus softer crumbs. The hole size did not reach levels found by others with high hydration doughs, which may be due to such factors as fermentation duration and expertise in the techniques of stretch-and-fold, shaping, and scoring.

crusts
Figure 4. Effect of hydration level on loaf size.
barchart
Figure 5. Barchart showing the height of loaves as hydration increases.

Additional differences are observed among the loaves. The 60% bread browned much faster than the others, and its crust failed to develop shine and crackle. This is likely due to the fact that the tagine cooking method, a local variant of the well-known Dutch oven cooking method, relies on the bread’s own steam being released inside the cooking vessel. The low hydration dough would have released less steam than the others, failing to regulate the temperature inside the vessel, so that browning was possible even while it was covered. The lack of steam failed to make the crust glossy, an effect of starch gelating in the presence of water. However, there was still too much moisture to allow the crust to fully dehydrate, so it did not get crisp or make the characteristic crackling noises upon cooling that signal a superior crust.

Grigne width increased as hydration increased, while ear height (never especially high) decreased. Loaf height increased and then decreased as hydration level increased. However, we found that a confound was introduced during experimentation. Doughs were mixed in ascending order of hydration, and despite being spaced out in time to some degree, they were often ready to be baked before their predecessor had left the oven. Meanwhile, the room was heating up, accelerating the rate of yeast activity and thus proofing. The last loaf was therefore likely overproofed. Its reddish crust corroborates this, a sign that much of its starch had been converted to sugar, which is used in a browning reaction. This overproofing would contribute to a lack of height and ear development, so we cannot conclude that its hydration level is to blame.

Discussion

The crust of the 60% dough suggests that for lower hydration doughs, an additional source of steam is needed. Its crumb, however, was excellent for a dense bread, indicating that the difficulty of developing the gluten was not a barrier to good bread. This surprised us, as we were completely ready to sacrifice the 60% dough to the compost bin gods.

Nor was the high hydration level of the 80% and 90% doughs a barrier to working with them, contra some accounts in the literature. Higher protein flours, like King Arthur Bread Flour, absorb more water than lower protein flours such as all-purpose flour, so reports that 90% hydration dough is a pain in the ass may be due to poor flour choice. The 80% dough in particular was reported to be “a fucking delight” by one lab technician, who is also the PI and sole author.

The primary contribution of this work is to show concretely the textures of both dough and final product that can be expected at these landmarks in hydration space when working with King Arthur Bread Flour. However, these findings are not comprehensive, as these doughs were subject to short fermentation times relative to current trends in artisan baking, and were executed by an experimenter who has not actually read the books on which this recipe was based. Regardless, the predicted trends were supported by the data: higher hydration appears to cause greater oven spring and more open crumb structure.

Conclusions

We conclude that 80% hydration is an excellent ballpark for those desiring oven spring and open structure in breads made with King Arthur Bread Flour. We cannot generalize from these findings to other flours, as their different protein and ash contents would make the hydration levels map onto different outcomes.

Additional research is needed to further improve oven spring. We suspect that a large factor is the difficulty of scoring soft doughs, but additional factors are of great interest. Similarly, a followup study on proofing levels of high hydration doughs (see https://forums.egullet.org/topic/82234-demo-proving-bread/) would be useful to determine what heights the 90% dough is actually capable of.

Appendix: Importance of Lid

In a pilot study, we found that when the lid of the cooking vessel is removed from the oven during the uncovered phase of baking, it cools down, raising the concern that it might crack if replaced into a 500 degree oven for the next loaf. Thus, the second loaf was baked uncovered. As both loaves were from the same batch (of a different recipe than that given here), this provided a controlled study of the effect of covering the dough while baking it. The results were quite pronounced, as shown in Figure 6. Not only oven spring, but also crust texture and color, were affected. Note that flour coverage varies due to unrelated factors. Covered initial baking was found to be a far superior method for wet doughs.

tagine_study
Figure 6. Left, bread baked covered for the first half of baking. Right, bread baked uncovered for the entire duration of baking.
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