Also Known as Water Hydration or Water Absorption Capacity (WAC)
What is Water Absorption?
Water absorption is the amount of water taken up by flour to achieve the desired consistency and create a quality end-product. It is the optimal amount of water you can add to a dough before it becomes too sticky to process.
Water absorption is usually defined by flour weight. For example, 60% water absorption means 60 lbs of water is used to hydrate 100 lbs of flour.
How does water absorption work?
When flour and water are mixed together, water molecules hydrate the gluten-forming proteins gliadin and glutenin, as well as damaged starch and the other ingredients. The hydration process is achieved when protein and starch molecules create hydrogen bonds and hydrophilic interactions with the water molecules.
Particles hydrate by rubbing against each other and contacting water. Process parameters such as type of mixer, beating arm, water flow and pressure remove the hydrated surface layer and expose a new layer of the particle to the excess water so the water diffusion process can continue.
Water absorption influences the following parameters of baking and bread:
- Loaf volume1
- Fracture stress of bread crumb1
- Bread yield2
- Final products attributes3
- Shelf life3
How to measure water absorption?
A farinograph is usually used and can provide an approximate value for water absorption.
The test is based first on the determination of the optimal amount of water to achieve a consistent Brabender Unit value or BU. The amount of water required to produce this consistency is the water absorption of a flour. The analysis of the typical farinograph curve yields important quality parameters such as:
- Arrival time to first achieve 500 BU
- Optimum mix time, also called dough development time
- Departure time
- Mixing Tolerance Index
- Dough stability4
Water absorption levels will vary from 50–54% in a cookie formula, 60–62% in a standard white bread formula, and 80-90% in an artisan-type Ciabatta formula. When developing with sprouted flour, the increase in enzymatic activity in the flour will increase water absorption and maillard reaction.
Influencing factors of flour water absorption:
- Starch: About 46% of the total water absorbed is associated with the starch.
- Proteins: About 31% of the total water absorbed is associated with the proteins.
- Pentosans: About 23 % of the total water absorbed is associated with the pentosans.
- Vital wheat gluten (VWG): When added to the formula, it will increase the water absorption and impart greater stability to the dough.5
- Other water binding ingredients like fiber, eggs, bran and hydrocolloids (gums).
Under- and over-absorption in bakery products
Different bakery products require different water absorption or hydration levels. Each level is unique for each kind of baked good to achieve the desired dough consistency and finished product characteristics.
The following are common problems that can occur during mixing. Both under- and over-absorption lead to quality issues in the dough and finished product:6
- Zghal, M. C., M. G. Scanlon, and H. D. Sapirstein. “Effects of Flour Strength, Baking Absorption, and Processing Conditions on the Structure and Mechanical Properties of Bread Crumb.” Cereal Chemistry Journal 78.1 (2001): 1-7.
- Puhr, D. H., and B. L. D’Appolonia. “Effect of Baking Absorption on Bread Yield, Crumb Moisture, and Crumb Water Activity.” Cereal Chem. 69.5 (1992): 582-86.
- Pyler, E. J. “Physical and Chemical Test Methods.” Baking Science & Technology. Merriam, Kan.: Sosland Pub., 1988. 851-71.
- Serna-Saldivar, S.O. “Quality Control of Cereal Grains and Their Products.” Cereal Grains: Properties, Processing, and Nutritional Attributes, CRC Press, Taylor & Francis Group, 2010, pp. 491–493.
- Sumnu, S.G., and Sahin, S. “Functions of Ingredients in the Baking of Sweet Goods.” Food Engineering Aspects of Baking Sweet Goods, CRC Press, Taylor & Francis Group, 2008, pp. 37–39.
- AIB International. Bread Manufacturing Process, Distance Learning Course, “Module 02 – Mixing.”https://www.aibonline.org/Start-Your-Training/Baking/Baking-Foundations/Bread-Manufacturing-Process-Online, 2018.