Measuring the Viscoelastic Properties of Wheat Flours

The Alveograph from CHOPIN Technologies enables the measurement of viscoelastic properties of wheat flours. The test involves producing a test sample of dough, which is deformed into a bubble under the action of air pressure.

This mode of expansion reproduces the deformation of dough which happens during fermentation, under the influence of the carbonic gas released. It is tailored to the following applications:

  • Choosing the best additives to improve the quality of finished products
  • Detecting insect-damaged wheat
  • Selecting, characterizing and classifying wheat and flours depending on their intended use
  • Specifying and optimizing wheat and flour blends
  • Analyzing the influences of adding gluten, deactivated yeast, proteases, or of salt content, on the viscoelastic properties of the dough
  • Checking product specification compliance

The early 20th century was a time of extensive research to better control and understand the properties of flours used to make quality bread. Marcel Chopin contributed to this effort in 1920 and filed a patent describing the Extensometer (French patent no. 525.986).

The Extensometer works by simulating the expansion of a cell in the dough, which it reproduces by expanding a dough disk which was previously prepared, under precise conditions. In 1937 the invention was supplemented (French patent no. 925-017) when Marcel Chopin himself added an extractor kneader to his invention and the Alveograph was created.

What is an Alveograph?

The Alveograph is a tool for measuring the characteristics of wheat flours based on the observation of the deformation of a dough bubble. An Alveograph is always made up of two inseparable parts: the Alveograph and the kneader.

The kneader-extractor is undoubtedly the most crucial part of the assembly, despite being less spectacular and photogenic. Successful kneading is 80% of a successful test. Technically, the kneader is designed to carry out optimal kneading of a 250-gram flour mixture with 50% added water (15% H2O base).

Next, is the constant hydration test, which involves one minute of mechanical kneading followed by one minute of manual kneading and then a further six minutes of mechanical kneading.

As it ensures that all the flour undergoes hydration and kneading and that there are no remaining places with unhydrated flour, the minute of manual kneading is crucial. The direction of rotation of the mixer (the kneading element) is reversed at the end of this period. This is to push the dough through a calibrated window that is utilized to establish the thickness of the piece of dough.

It is thought that this part is where Marcel Chopin’s inventive genius was demonstrated most strongly. It is possible not only to push the dough out of the kneader in a straight line but also to align the protein chains to form a homogeneous gluten network by giving the mixer its particular curved shape.

Many attempts have been made to work with doughs from other kneaders, but none have been able to reach the levels of reproducibility and repeatability achieved with the original kneader-extractor.

Five pieces of dough are cut, rolled, cut into discs, and placed in a resting chamber as they are extracted. Performed under specific temperature and humidity conditions, this phase is also crucial to the success of the test. It is during this period that the protein chains stop becoming structured.

Next, the piece of dough is put onto the Alveograph and pressed at a set speed to give it a defined thickness. Then it is inflated with a calibrated flow of air while the system records the alteration in pressure inside the bubble over time until the film of dough breaks.

In order to acquire the final result, this operation is repeated on the five pieces of dough, and the five measurements are averaged. The Alveograph’s curve exhibits the pressure as a function of time.

What the curve shows is closely comparable to what happens when we try to inflate a balloon. The piece of dough resists deformation at first because and the internal pressure increases, because air is continuously added and the volume receiving it is small.

The more the dough resists, the higher the pressure. On the curve, the maximum value “P” represents the dough’s tenacity (resistance). This is known as the dough’s “consistency” to a baker.

What is an Alveograph?

As with a balloon, the piece of dough will start to form a bubble once the resistance is exceeded (due to the addition of air). The bubble’s volume increases extremely fast in the case of dough, and its internal pressure drops which causes the curve to begin descending. If the dough is not very elastic this will happen faster.

In order to measure the “elasticity index”, the rate of the decrease between the “P” value and the pressure value at a particular point on the curve is utilized. This elasticity represents the dough’s capacity to retract after deformation, which explains why some pizza doughs have an unfortunate tendency to be the wrong size.

The bubble continues to deform until the dough film is so thin that it breaks, just as a balloon would burst when over-inflated. Before reaching this breaking point, the time elapsed is also expressed as a distance and represents the “G” or “L” that both correspond to the dough’s extensibility. For bakers, this concept expresses the dough’s ability to stretch.

Some other parameters are also quantified, also known as the “baking strength”, “W” represents the total area under the curve. To compare tenacity and extensibility, it is also possible to calculate the P/L ratio.

Each of these properties is dependent on the quality of the proteins (which have different levels of extensibility, tenacity, and elasticity), the damaged starch, and the ash content (which increases tenacity), together with the numerous added ingredients.

Today, the Alveograph is the preferred tool of millers, who utilize it to choose and mix their wheat, inspect and improve flours, and comply with specifications. It is an internationally recognized standard method (ISO 27971, AACC 54-30.02, ICC 121, GOST 51415-99 …).

Additionally, it is widely employed in the secondary processing industry among ingredient suppliers, research institutes, breeders, and others. The Alveograph is not limited to a particular type of wheat or flour, unlike some traditional methods.

It is just as effective for processing soft and hard wheat (there is even a protocol for durum wheat) and flours for crackers, cookies, all types of bread (sandwich bread, baguettes, and flatbreads), pizza and pasta.

Through completely open testing conditions (speed, time, and temperature) and new protocols (e.g., with adapted hydration), the Alveograph continues to evolve today, enabling it to adapt to modern challenges and is recognized both for quality control and as the go-to instrument for developing new products.

This information has been sourced, reviewed and adapted from materials provided by CHOPIN Technologies.

For more information on this source, please visit CHOPIN Technologies.

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