Flour absorption measure

by Emily Wilson
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The Chopin Consistograph is a relatively new way to quickly and accurately measure the water absorption capacity of flour and dough mixing properties. Besides its laboratory use, the Consisto-graph has proven to be an efficient tool to instantaneously measure the consistency of dough directly taken from a baker's mixer.

The Consistograph received first approval by the American Association of Cereal Chemists in 1998, showing excellent results during a collaborative study. It can be used as a quality control tool for reception or expedition, as a control tool in the plant or as a development tool.

The Consistograph also increases the efficiency of Chopin's Alveograph — the industry's standard for dough quality — especially on the hardest types of wheat. It also allows the flour to be tested at adapted hydration (constant maximum consistency), also called constant consistency.

The Consistograph is composed of a mixer connected to a recorder-calculator, the "Alveolink NG," which registers the pressure in millibars and transfers the data to a computer.

The Alveolink and its touch screen create an intuitive interface between the Consistograph and user. The test is user non-dependent, and because the device can be cleaned easily, many tests may be performed per shift.

The Consistograph mixing bowl is equipped with a pressure sensor. A special double arm kneader is used to increase the mixing intensity. A static rod, fixed on the moveable side of the mixer between the two arms, helps keep the dough from balling and increases mixing efficiency.

The pressure sensor is directly connected to the Alveolink, which acquires and processes the data. The Alveolink also manages the test time, allowing an autonomous measurement and automatically stopping the device at the end of the test.

CONSTANT HYDRATION. The Alveograph works at constant hydration. Flour is hydrated according to its moisture content. The basis of the calculation on the Alveograph (as well as the Consistograph first test) is to form a dough hydrated to 50% on a 15% moisture content basis. It can also be calculated as 76.47% hydration on dry basis.

This protocol has been used since the introduction of the Alveograph and is considered an international standard. The constant hydration protocol provides valuable data.

For example, the increase of P value is an indicator of the water absorption capacity of flour. This behavior is useful for the Consistograph procedure because it makes it possible to evaluate the flour absorption capacity.

The principle of the Consistograph is based on the measurement of a pressure on the mixer's walls. The blade pushing the dough against the pressure sensor initiates this pressure. The "F value" depends greatly on the dough consistency. If it is too soft, the dough will not apply much pressure to the sensor.

Unlike other existing devices, the Consistograph does not measure a torque, and the mixing device is not always in contact with the dough. As a result, the Consistograph measurement is more sensitive to the dough cohesiveness. Stickiness does not appear to be a factor leading to better tolerance; in fact, the opposite has been observed.

At constant hydration, the dough is tougher yet "underhydrated." In that case, the recorded pressure will be high (see top chart at left). A direct correlation has been established between the highest pressure on the curve and the water absorption capacity of the flour. This highest value is called PrMax (maximum pressure) and is automatically calculated by the Alveolink NG.

When performing a test at constant hydration, the PrMax value is registered. This value is directly converted into a water absorption capacity, depending on the consistency the user wants to reach.

In the standard protocol, the hydration will be given for two consistencies: 2200 millibars and 1700 mb. For a better understanding, the water absorption capacity can be calculated on a different moisture content basis (see bottom chart).

ADAPTED HYDRATION. This curve is obtained on the Consistograph, using the water absorption determined previously. Several values can be measured on this curve (see top chart below), including the time to reach PrMax, which is related to the ability of the flour to form a dough and reach the desired consistency. The tolerance is measured by the time during which the pressure is higher than PrMax minus 20%.

The 250 seconds drop and 450 seconds drop show the capacity of the dough to resist mixing. These data are most often related, but one can sometimes observe curves having similar drop at 450 seconds whereas the 250 seconds drop is different. This gives a good indication of the dough resistance to mixing.

Different kinds of flour and their behavior during mixing is shown in the bottom chart at left. Time to reach PrMax tends to decrease on weak flours. Weak flours also tend to have less stability and a higher drop (even if this parameter is calculated at 240 seconds or at 480 seconds). The stronger flours have greater stability and a lower drop.

LABORATORY APPLICATIONS. Water absorption is a key factor when dough has to be formed and greatly depends on the dough consistency.

One of the strengths of the Consistograph is its ability to provide, in a single test, two water absorptions for the two consistency levels. One of these two consistencies is fixed in all the devices (WA) and can be used for quality control of entering materials.

The user is able to choose the second consistency, which can correspond to the real consistency of a dough from the baker's mixer. The user has the ability to not only perform a quality control test and compare the results with the test from the supplier, but also receives a valuable indication on the quantity of water to add to the flour on the process line.

Water absorption is not the only important aspect of the Consistograph. For example, the flour must have the capacity to absorb the incoming water without becoming sticky. On the Consistograph, stickiness seems to act as a depressive factor. Consequently, if adding water to flour makes the dough sticky, the curve drop will be high, indicating a difficulty operating dough.

Dough behavior during mixing is also a good indicator of flour quality and fitness to process. Water absorption can be measured on the Consistograph in only four minutes and dough behavior during an 8-minute mixing cycle. This provides a quick determination of the flours entering the bakery.

ADDITIVES, INGREDIENTS. All additives and ingredients having an effect on dough behavior during mixing can be measured on the Consistograph.

Ingredients and additives that will make a flour well-suited for a particular process are of primary importance nowadays. Enzymes are used more often, and the Consistograph has shown to be well adapted to register the enzymes' effect on dough rheology during mixing.

Many ingredients are used in baked products, from the simplest formula using flour, water, yeast and salt to one incorporating milk, fat, sugar and sometimes chocolate or fruit. Since flour is a major component of the final product, it is important to measure the effect of the different ingredients on the dough rheology.

The ingredient quality may differ, causing different interactions with the flour. The Consistograph will register the changes that occur when different products are incorporated into the dough. A test for salt revealed that the dough's stiffness increases as soon as salt is incorporated into the dough. This phenomenon, well known among bakers, is registered by the Consistograph.

Some tests show that the consistency increase when salt is added depends on dough strength. The stronger the dough, the higher the increase. Adding salt reduces the stickiness of the dough. This curve shows that the Consistograph is sensitive to real consistency and that stickiness acts as a negative factor on the dough tolerance.

Chopin tested a Danish pastry formula to see how the different ingredients affect the Consistograph curve. The chart at left shows the mixing properties of the same flour incorporating the different ingredients of the formula (except sweeteners).

The dark blue curve (1) shows the mix of flour and water. Water hydration of this flour is minimal and therefore does not permit real dough development. The pink curve (2) corresponds to flour plus water plus eggs; real hydration is given by the eggs.

The yellow curve (3) corresponds to the replacement of eggs by water. The consistency was shown to be lower, indicating an effect of eggs on the dough consistency.

To reach the light blue curve (4), salt was incorporated in with flour, water and eggs. The last two curves (5 and 6) indicate the sugar effect.

The difference between the two curves corresponds to the way sugar is added (in the flour or in the hydration water). It is interesting to see how each of these components acts on the dough rheology. Further studies should be made to explain these behaviors and to determine how the quality or type of ingredients interacts with the flour.

The Consistograph, in the laboratory, can also be used in research and development to test formulas or to measure the effect of a new additive or ingredient.

PROCESS APPLICATIONS. It is possible, by sampling directly from a baker's mixer, to measure the instantaneous consistency of the dough. If sampling is done every period of time, it is easy to plot a curve indicating the consistency versus time.

Chopin's tests have shown that a spiral mixer is more powerful than an oblique axis mixer. Each mixer is different, so knowing exactly how the mixer works is a great help for the baker. The Consistograph can also monitor the aging of the production mixer. It is possible to measure the real incidence of mixing times and water addition on different mixers and different flours.

Chopin's application department tested the capacity of the Consistograph to mix a dough suitable for bread making (see photo above). The results showed that, with some modifications, it is possible to produce loafs from 150 g of dough similar to the reference bread making procedure as long as aspect and volume are concerned.

Arnaud Dubat is the flour department director for Chopin S.A., Villeneuve la Garenne, France.