What is sourdough hydration?
A sourdough’s hydration level is a measure of the weight of water in the dough in relation to the weight of the flour in the dough, expressed as a percentage i.e. 78% hydration. The higher the hydration level of a dough, the wetter and stickier it becomes.
A 78% hydration dough contains 78grams of water for every 100grams of flour. Let’s say your sourdough recipe calls for a 78% hydration and 500 grams of flour; the weight of water you need to add to the flour to achieve a 78% hydration dough is 500grams of flour x (78/100) = 390grams of water.
How does a dough hold in water?
When flour comes in contact with water, the protein and starch molecules of the flour absorbs water and interacts with it; protein in the flour interacts with water to form gluten, while the starches acts like a magnet and pulls water molecules towards it, coating its surface.
The longer the dough is mixed, the more water the flour absorbs, which transforms the dry and crumbly flour and water mixture into a coherent dough mixture.
As the flour and water mixture is kneaded and mixed, the protein, starch and water molecules rub against each other, and intensifies water absorption by the flour.
The gluten that is formed during mixing also helps the dough to retain moisture. The gluten is an impermeable layer, which does not allow gas or water to pass through. As more gluten is developed from kneading and mixing the dough, the dough has a better ability to trap water, leaving less water on the outside of the dough, resulting in a drier and less sticky dough.
What is considered low, medium and high hydration?
| Hydration | % |
| Low | Less than 65% |
| Medium | 65% – 75% |
| High | More than 75%, up to 110% |
The hydration level of the dough only serves as an approximate guide to the amount of water required to achieve a desired feel and consistency of the dough as the flour’s ability to absorb water varies depending on the type of flour that we use and the humidity in the air.
Whole grain flour absorbs more water than white flour, hence to achieve the same desired feel and consistency of the dough, the hydration level of the whole grain dough is typically 10-15% higher than the hydration level of white dough.
When baking in a more humid environment, the air contains more water vapor, which is absorbed by the flour, increasing its moisture content. Flour mixed in a more humid environment requires less water to achieve the same dough feel and consistency than flour mixed in a less humid environment.
Multigrain sourdough recipes that calls for the inclusion of seeds and nuts also requires a higher hydration level as the seeds and nuts has the ability to absorb a high quantity of water. To reduce the tendency for the seeds and nuts to rob moisture from the dough, the seeds and nuts are usually soaked in boiling water (these are called soakers) for a few hours prior to being incorporated into the dough.
Hence, while the hydration level of a recipe gives us a close approximation of the water requirements of the dough, the baker has to fine tune the hydration level of the day’s dough according to the changing requirements of the ingredients and humidity of the day to achieve a repeatable and consistent dough texture every day.
How does hydration level of the dough impact the baking process?
Impact of low hydration doughs on the baking process
- Very dry doughs (less than 65% hydration) develops gluten poorly as there simply isn’t enough water to hydrate the flour (gluten only forms in the presence of water); requires more mixing time.
- Drier dough feels stiff and tears easily; is difficult to shape.
- Drier dough ferments slower; bulk fermentation and final proofing time is increased.
Since low hydration dough already has difficulty developing gluten, causing it to tear easily when shaped, we should avoid combining whole grains flour, seeds and nuts with a low hydration dough. The sharp particles of whole grains, seeds and nuts tends to severe the gluten matrix of the dough, further damaging the already insufficient gluten network of the dry dough. If we insist on baking low hydration dough with whole grains, seeds and nuts, we will end up with a flat, dry and dense loaf.
Impact of high hydration doughs on the baking process
- Very wet dough (more than 75% hydration) develops gluten poorly as the dough struggles to absorb and retain the excess water; requires more mixing time.
- Very wet dough is slack and doesn’t hold its shape well; scoring is likely to flatten the dough.
- Wetter dough ferments better; bulk fermentation and final proofing time is reduced.
The basinage technique assists gluten development of very wet dough. When mixing or kneading very wet doughs, mix the dough by incorporating water in stages. During the first mix, hold back a portion of the water, so that the dough is relatively drier, which allows gluten to be developed easily. When the dough has gained sufficient strength, introduce the remaining water in stages and mix only until the water in incorporated.
Very wet dough although mixed to full gluten development, is generally still very weak and has difficulty holding its shape. We can help the dough to gain strength through the accumulation of acids from fermentation by allowing the dough to proof overnight for 10-12 hours in the refrigerator.
The cold environment of the refrigerator slows down yeast fermentation dramatically so that the dough does not overproof. In the cold environment, lactic acid bacteria continues to release acid into the dough, which tightens the gluten structure, giving the dough sufficient strength to hold its shape throughout the baking process.
How does hydration level impact the baked loaf?
The hydration levels of your dough is the main factor in determining the final characteristics of your crumb and crust structure. A high hydration dough results in a soft, light, airy and open crumb with a thin crust, while a low hydration dough results in a drier, denser, closed crumb structure, and a thicker crust.
A high hydration dough is looser and more supple compared to a low hydration dough. The wetter dough is able to expand freely from the rising pressure of carbon dioxide gasses during fermentation, causing the crumb to open up forming large holes, and the crust to remain thin and crispy from the wide separation between the gluten layers.
A low hydration dough is stiffer compared to a high hydration dough. The low hydration dough’s expansion is restricted from the increased stiffness of the dough, causing the crumb to open up less, forming smaller holes, and a thick crust is formed from the narrow separation between the gluten layers.
A high hydration loaf tends to have a mild sourness (akin to yogurt) while a low hydration loaf tends to have a stronger sour bite (akin to vinegar).
Lactic acid bacteria fermentation releases lactic acid and acetic acid into the dough which gives the dough its sourness; lactic acid has a mild sourness while acetic acid has a strong sour bite. Since the development of lactic acid favors a wetter dough, while acetic acid favors a drier dough, a high hydration loaf tends to have a mild sourness while a low hydration loaf tends to have a stronger sour bite.
Very wet (more than 75% hydration) and very dry (less than 65% hydration) dough do not produce the best flavor.
With very wet dough, the challenge is to prevent the crust from becoming too dark, too thick, and too soft when cooled, hence negatively impacting the flavor of the bread. The greater internal moisture content results in increased absorption of water by the crust when the baked loaf is cooled. A thin and crispy crust can be achieved by ensuring the high hydration loaf is fully baked, to remove any excessive moisture in the crumb.
With dry doughs, the flour is not properly hydrated, and it barely breathes. A few more percentages of hydration can transform a dough that has limited flavor development to one that expands to its fullest flavor potential.
Conclusion
If you are just beginning your sourdough bread baking journey, I would highly recommend mastering sourdough with a hydration level of 75% first, which is ideal as the dough is not too sticky and difficult to handle, at the same time it produces a loaf with good volume, a light, moist and open crumb with a thin and crispy crust.
Advance bakers will push the hydration boundaries of the dough, going upwards to 100% hydration levels in the search for the ultimate light, airy, open crumb and thin blistering crusts. The successful bake of very high hydration loafs is a milestone in a sourdough baker’s journey, which signify the culmination of a deep understanding of the dough and the baking process.
I have written an article titled Secrets of Large Holes and Light Open Crumb Sourdough Bread, which explains in great depth the 10 main baking techniques to successfully bake sourdough bread of very high hydration levels. In the article we will talk about the basinage technique, autolysing, folding, fermentation, scoring, steaming and the use of the right flour.