What is an Alveograph?
The alveograph is a test that measures the baking performance of flours intended for the production of yeast-leavened bakery products. This test uses air pressure to inﬂate and stretch a thin sheet of dough to form a bubble, simulating gas/carbon dioxide release and retention during dough fermentation.
By determining the pressure and length of time it takes to burst the bubble, bakers will gain information about the dough tenacity, elasticity and baking strength.
The alveograph helps millers and bakers to:
- Classify wheats according to baking strength and define their end use or application
- Optimize the flour blends and streams at the mill
- Detect proteolytic activity (sprout damage) in wheat
- Evaluate the conformity of incoming flour at the bakery
- Adjust mixing time and water absorption
- Adjusting proofing conditions for given doughs (time, relative humidity, temperature)
- Decide on the use of dough conditioners (redox agents, emulsifiers, enzymes for strengthening or weakening of dough)
- Define which product to make according to quality of flour
Unlike the extensograph, which uses tensile strength by stretching the sample dough piece in only one direction, the alveograph subjects the dough to extension in two dimensions.1
The alveograph is a modified version of the extensometer which was invented by Marcel Chopin in 1920. The instrument was used to prove that the baking properties of bread were essentially dependent on the quality of French wheats.2
How does it work?
The test consists of the following steps:3,4,5
- Preparing 250 g of flour and a sodium chloride solution (2.5% weight/volume). The volume of water required to hydrate the flour to a predetermined value is adjusted according to the moisture content of the sample.
- Mixing and kneading in a chamber for about 8 minutes to form a dough of proper rheology and consistency.
- Dividing the dough into four equal parts that are extruded and sheeted with a roll to obtain a fixed thickness (12 mm) followed by dough resting.
- The dough sheets are cut into discs using a die, and are proofed in an isothermal (temperature-controlled) box.
- Automatic inflation of the dough disc by injecting air at constant pressure and flow rate until the resulting bubble bursts. The pressure inside the bubble and time it takes for the bubble to burst are recorded.
- The test is usually repeated several times, and the pressure/time parameters are averaged.
Parameters measured by the alveograph test:2,4,5
- P (y-axis): Maximum pressure required for the deformation of the sample or overpressure. P-value is graphically seen as the height of the peak and is related to the resistance of the dough to deformation (tenacity).
- L (x-axis): Maximum amount of air the bubble is able to contain. L-value is graphically seen as the length of the alveograph curve or distance at which the bubble ruptures, an indication of dough extensibility.
- Elasticity Index (Ie): Compares pressure after 200 mL volume of air have been blown into the dough test piece or bubble versus the maximum pressure (P).
- W: Indicates dough baking strength. W-value is graphically seen as the total area of the alveograph curve or total deformation energy. The area under the curve represents the energy required to expand the dough and is related to the strength (baking performance) of the flour. This area is generally much larger for hard wheat flours than for soft wheat flours.
The following figure represents a typical alveograph curve:
Official methods of analysis that make use of the alveograph:
- AACC International Method 54-30.1999 (Alveograph Method for Soft and Hard Wheat Flour)
- ICC Standard No. 121. 1992 – Method for using of the Chopin Alveograph (matrix: wheat flour; analyte: rheological Properties)
- Papageorgiou, M., and Skendi, A. “Flour Quality and Technological Abilities.” Engineering Aspects of Cereal and Cereal-Based Products, CRC Press (imprint of Taylor & Francis Group), 2014, pp. 130–131.
- Dubois, M., Dubat, A., and Launay, B. The AlveoConsistograph Handbook, 2nd edition, AACC International, Inc., 2008.
- Finnie, S., and Atwell, W.A. “Wheat and Flour Testing.” Wheat Flour, 2nd edition, AACC International, Inc., 2016, pp. 69–70.
- Chopin. “Alveolab Graph — Measure of dough tenacity, extensibility, elasticity and baking strength.” http://www.keydiagnostics.com.au/images/new2018/26%20Chopin/Alveograph/Alveolab%20LABgraph%20Brochure%20KD%2010-17.pdf. Accessed 20 May 2018.
- Serna-Saldivar, S.O. “Dry-Milling Processes and Quality of Dry-Milled Products.” Cereal Grains: Laboratory Reference and Procedures Manual, CRC Press, Taylor & Francis Group, LLC, 2012, pp. 151–153.