An example of Chopin Alveograph

Alveograph (W Index & P/L Values In Flour)

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The alveograph is a tool used to measure the rheological performance of flour through a specific laboratory test. It primarily evaluates the dough’s ability to withstand fermentation, which indicates the “strength” of the flour, as well as its resistance and elasticity.

Ultimately, the alveograph provides information about the expected behavior of the flour during fermentation. It helps to determine the flour’s resistance to over-fermentation (how “strong” it is) and measures its viscoelastic properties, specifically its extensibility and elasticity.

It is important to note that the alvograph (and consequently, the W index) was specifically designed for European flours made from soft wheat, with a relatively low protein content. As a result, its use is primarily limited to Europe, particularly France (where it was invented) and Italy; Outside of these two countries, the use (and publication) of the W index is quite rare and mainly restricted to pizza flours (for marketing reasons, obviously).

The reason for this is that when it comes to soft wheat, there is often no direct correlation between the protein content and the quality of the gluten produced. Two flours from different types of soft wheat may yield dough with different properties and strength, even if they have the same protein content; And this is exactly the purpose of the alveograph test (and the W index) – to provide information on the gluten quality of these flours and distinguish between them.

On the other hand, when it comes to hard or stronger wheat, there is an almost direct correlation between the protein content and the quality of the protein (gluten). In general, in flours made from such wheat, a higher protein content translates to more gluten and stronger flour. Therefore, there is no reason (or need) to use the W index in flours milled from stronger wheat.

Additionally, the alveograph is not suitable for testing hard wheat flours with higher protein content because it is specifically designed for European soft wheat; As a result, the alveograph may provide unreliable and inconsistent results when used to test stronger flours. For testing the properties of stronger flours, it is customary to use the Farinograph, which provides more accurate information.

The process for obtaining the alveograph is as follows:
1. A small sample is taken from the dough made with the flour being tested. This sample is then flattened into a disk shape.
2. The flattened sample is attached to a surface and inflated to a dough “bubble” using air pressure.
3. A dedicated device measures the relevant parameters.

The alveograph consists of three values: P, L, and W.

The P value measures dough resistance, indicating the pressure required to pop the dough bubble (indicating the “strength” of the flour).
Flours with a high P value typically have a high protein content.

The L value measures dough extensibility, indicating its ability to stretch.

The P/L ratio represents the viscoelastic properties of the flour’s gluten.
A P/L ratio of 1 indicates a balanced gluten with equal elasticity and extensibility.
A P/L ratio of less than 1 suggests a gluten that is more extensible, meaning it can stretch more easily.
A P/L ratio greater than 1 suggests a gluten that is more elastic and resistant.

The W index, also known as the “bread baking index,” represents the area under the curve (multiplied by 6.54). It indicates the energy required for the dough bubble to burst, or in simpler terms – the strength and resistance of the dough for baking purposes. 

Generally, flours with a higher W index can absorb more water and result in a final product with a larger volume due to stronger gluten. However, it is important to note that this is not always the case, and depends on the specific values of P and L.

W index usually ranges from 45 (indicating very weak flour) to 400 (indicating a very strong flour). The table below summarizes the W index associated with different baking applications:

WComments
120 or lowerVery weak flour. Not suitable for baking
120-160Weak flour. Suitable for baking cakes and cookies
160-250Medium-strength flour. Suitable for baking goods that do not require a strong dough, such as soft rolls/buns and various pastries
250-310Strong flour (typically made from hard wheat or a combination of hard wheat). Suitable for bread making
310 or higherVery strong flour made from hard wheat. Suitable for doughs that require full strength and high elasticity

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