CHAPTER 1
The Chopin Alveograph In 1905, Hungarian scientist Jenö von Hankoczy designed an apparatus that became known as “Hankoczy’s gluten tester” (Hankoczy 1920). The apparatus provided a means for pressing moist, crude gluten into a thin sheet between two plates that each had a round opening 2 cm in diameter in the middle. The plates, with gluten pressed in between, then were mounted in a device that joined the lower plate to a vessel into which air could be compressed, while the upper plate joined another vessel from which air would be displaced. Air in the lower vessel was compressed by introducing mercury from a bulb elevated to a height that provided enough pressure to stretch the gluten. The gluten expanded into a bubble through the round opening in the upper plate. A simple gasometer measured the air displaced from the upper vessel by the expansion of the gluten bubble. Thus, the maximum volume of the bubble before it burst could be measured. Hankoczy later improved this instrument so that the pressure of the air in the lower vessel also could be measured, thus improving the precision of the evaluation of the “strength” of the gluten sample. A later version of this testing device allowed a disk of dough to be stretched instead of a disk of gluten. Because the importance of temperature in the rheological testing of doughs had not yet been recognized, none of these early instruments had any temperature control. In the 1920s, Marcel Chopin became interested in the possibility of using dough-testing instruments in place of baking tests to assess the baking quality of French wheats. With no prior knowledge of Hankoczy’s developments, he attempted to develop a test that would simulate, as closely as possible, the process that dough undergoes in bread baking. Chopin’s approach was based on the then-current concept of the physical condition of developed dough and its changes during the bread-baking process. He considered the dough coming out of a mixer to be in a more-or-less compact state that then was transformed into thin membranes during fermentation and baking. These membranes solidified or were set by heat in the oven and divided bread into innumerable cells filled with gas. If the loaf was well developed, the membranes were thought to have been stretched to the limit of their ability to withstand the mechanical forces set up during baking. The more easily the dough could be drawn into a thin sheet, the more complete would be the development of the loaf. Based on this model, Chopin designed an extensimeter to measure the plasticity of materials, especially wheat flour dough (Chopin 1921). Four years later, Bailey and Le Vesconte (1924) published an English version of the original French description of this extensimeter. The extensimeter was designed to measure 1) the “tenacity” of the dough, estimated by the effort necessary to force a uniform cylinder of dough to take a definite form in a fixed period of time, and 2) the ability of the dough to be stretched into a thin membrane. To accomplish these measurements, the dough had to be in the form of a small cylinder, firmly attached to the apparatus and held at constant temperature, and the law of the variation of the force to which the dough was subjected had to be uniform in all trials, because the material tested was irreversibly deformed by the applied force. The original version of the instrument was designed to meet all the above conditions. Later modifications of the original extensimeter gave better control over the size of the dough test piece and better recording of the air pressure at any time during the test (Chopin 1927). The distance between the two plates, and hence the dough thickness, was adjusted to 2.6 mm. Air pressure for stretching the dough piece was supplied by allowing water to flow from a bottle into a graduated buret.
Up to this time, no dough mixer was attached to the instrument. A homogeneous dough was made by mixing 333 g of flour, 5 g of sodium chloride, and 163 mL of water at 25°C for 8 min in a small mechanical mixer. The desirable flour moisture content was approximately 15%. Flour moisture was allowed to vary by up to 1% without adjusting the dough proportions. In Chopin’s original extensimeter, dough was rolled into a cylinder from which sections were cut for testing. Later, Bailey and Le Vesconte (1924) described the dough preparation procedure as follows: The mixed dough was removed from the machine, rolled out into a sheet about 18 mm thick on a glass plate, brushed lightly with oil, covered with a damp cloth, and allowed to stand for 25 min. Test pieces 50 mm in diameter and 18 mm thick were cut with a metal cylinder and taken for testing. In the 1930s, Chopin (1935, 1937) designed a unique dough mixer for use with his extensimeter. The mixer had a hinged side arranged so that the force exerted against it by the developing dough was registered on a chart. The force was a function of the relative plasticity of the dough and changed progressively during mixing. On the opposite side of the mixer bowl, Chopin designed a gate that could be opened to create a horizontal slot 6 cm wide. When the dough was mixed to its optimum strength, the motor driving the mixing blade was reversed, the gate was opened, and a flat band of dough was extruded under a roller onto a template. Portions of the dough were cut off and flattened with a metal roller between guides that determined the thickness of the pieces. Chopin gradually improved his extensimeter until it developed into what is known today as the Chopin Alveograph (Table 1.1). The instrument is manufactured by Chopin Technologies, Villeneuve la TABLE 1.1 Different Alveograph Types Since 1982 Device
From Serial No.
MA 82 MA 87 MA 95 NG
2800 3436 4440 5000
Distinctive Elements Pump for generating air, no display Display of temperature and integrated timer Improved safety and automatic bubble blowing Display on mixer indicating two temperatures (mixer and alveograph) Different design Possibility of integrating the consistograph Improved mixing bowl temperature control
Fig. 1.1. Chopin Alveograph MA 82. (Courtesy Chopin Technologies)
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Garenne, France. In 1982, the manufacturers presented a new model, the alveograph MA 82 (Fig. 1.1), followed in 1987 by the MA 87 (Fig. 1.2). The MA 95 was an improvement on the MA 87, with an automatic inflation of the bubble. In 1998, Chopin developed the alveograph NG series, introducing the consistograph and the alveoconsistograph (Fig. 1.3). Table 1.2 summarizes the specifications of the Chopin Alveograph. THE INSTRUMENT The Chopin Alveograph consists of four main components: the mixer (Fig. 1.4A); the actual dough-bubble-blowing apparatus, or alveograph proper (Fig. 1.4B); the recording manometer or Chopin Alveolink calculator (Fig. 1.4C); and the printer (Fig. 1.4D). The Mixer he engineering details of the MA 87 and MA 95 mixers and the NG mixer (which also functions as an extruder) are shown in Figures 1.5–1.7, respectively. A schematic cross section of the MAtype mixer is shown in Figure 1.8. The mixing blade (Fig. 1.8D) rotates counterclockwise for mixing and clockwise for extrusion. It has a sigmoid shape and is made from brass. Because brass is a relatively soft metal, the blade may deform over time, adversely affecting the results (see Chapter 7). The shaft of the kneader fits into a bearing of a speed reducer connected to a 380-V, three-phase motor (220-V single-phase motor for the NG models). The kneader rotates at 60 ± 1 rpm.
Fig. 1.2. Chopin Alveograph MA 87. (Courtesy Chopin Technologies)
Fig. 1.3. Chopin Alveograph NG. (Courtesy Chopin Technologies)
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The mixer is cooled by a water reservoir, which may be connected to either tap water or a water bath. It also is fitted with a heating jacket to keep the mixer temperature at 24 ± 0.5°C. The top opening of the mixer is covered by a plastic lid with a hole in it, through which salt solution is added to the flour. The lid is equipped with a safety magnet, which shuts off the motor as soon as the lid is removed. The MA 82 and MA 87 alveographs also have another safety switch at the bottom of the mixer to protect the operator. This switch must be turned off before any mechanical work can be done on the instrument. The alveograph NG mixer (Fig. 1.9) consists of an evolution of the MA 87 mixer bowl. It includes all the features of the previous alveograph and keeps all the technical specifications shown in Figure 1,8. The main differences consist of the following: • The mixer integrates the cooling system; thus, parts A and B of Figure 1.8 disappear. • The safety systems have been improved to reach requirements of different international organizations.
TABLE 1.2 Chopin Alveograph Specifications Property Rotational frequency of the mixer blade Distance between the blade and the bottom of the mixer Distance between the blade and the side of the mixer Height of extrusion gate (left) Height of extrusion gate (right) Width of extrusion passage Height of guide rails Diameter of the sheeting roller Large Small Inner diameter of the dough cutter Diameter of the opening in the upper brass plate of the alveograph proper (diameter of the test piece to be inflated) Theoretical distance between upper (moving) and lower (fixed) brass plates of the alveograph proper once they have been clamped down to the thickness of the test piece before inflation Volume of rubber bulb (MA 82–87) Linear speed of the periphery of the recording drum Period of rotation of the recording drum (or from stop to stop) Airflow pressure on the manometer (only for MA 82 alveograph) Length of the tube connecting the alveograph proper to the manometer (alveo NG) Inner diameter of the tube connecting the alveograph proper with the manometer (alveo NG) Temperature of the mixer Temperature in the resting compartments of the alveograph proper
Value 60 ± 1 rpm 0.1 mm 0.2 mm 5.4 ± 0.2 mm 5.5 ± 0.2 mm 50.0 ± 1.0 mm 12.0 ± 0.1 mm 40.0 ± 0.1 mm 33.0 ± 0.1 mm 46.0 ± 0.5 mm 55.0 ± 0.1 mm
2.67 ± 0.01 mm 18 ± 2 mL 5.5 ± 0.1 mm/sec 55 sec 60 mm 80 cm 4 mm 24 ± 0.5°C 25 ± 0.2°C
Fig. 1.4. Alveograph NG mixer (A) and alveograph proper (B) with the alveolink (C) and the printer (D). (Courtesy Chopin Technologies)
Fig. 1.5. Alveograph MA 87-type mixer.
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Fig. 1.6. Alveograph MA 95-type mixer (mixing bowl details).
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• The mixer is ready to be connected to the consistograph system by placing a sensor directly on the mixer wall and by replacing the mixing blade and the mixer wall (Fig. 1.10) (see Chapter 8 for details). The Chopin buret (Fig. 1.11) is graduated for a flour moisture range of 11.6–17.8%. (The Chopin buret may be replaced with any buret with a capacity of 160 mL and graduated in 0.25-mL intervals.) After mixing, the dough is extruded onto a receiving plate through a gate that, during the mixing stage, is closed by a shutter held in position by a screw (Fig. 1.8). The extrusion gate is 50 ± 1
mm wide, 5.4 mm high at the left, and 5.5 mm high at the right. The height of the extrusion passage can be adjusted by loosening the setting screws.
Fig. 1.9. Engineering details of the alveograph NG mixer, showing the safety switches (5 and 6), heating jackets (R1 and R2), kneader (1), extrusion gate (2), adjusting screws of the extrusion gate (19), extrusion-gate shutter and extrusion-gate shutter screw (8), and lid (12). (Courtesy Chopin Technologies)
Fig. 1.7. Alveograph NG-type mixer (mixing bowl details).
Fig. 1.8. Cross section of the alveograph MA 82, MA 87, or MA 95 mixer, showing the water tank (A), circulating water outlets (B), heating jackets (C), kneader (D), extrusion gate (E), adjusting screws of the extrusion gate (F), extrusion-gate shutter (G), extrusion-gate shutter screw (H), lid (I), hole in the lid (J), and extrusion plate (K). (Courtesy Chopin Technologies)
Fig. 1.10. Engineering details of the alveograph NG mixer in consistograph configuration, showing, in particular, the consistograph kneader (1), the specific mixer wall with static rod (8), and the pressure sensor location (5). (Courtesy Chopin Technologies)
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The Alveograph Proper The engineering details of the MA 82, MA 87, and NG alveograph parts are shown in Figures 1.12–1.14A respectively. Figure 1.14B shows details of the NG alveograph piston. Compared with the first hydrostatic models, the most distinctive feature of the MA 82 alveograph is the way air pressure is supplied for blowing the dough test piece into a bubble. Instead of generating this pressure hydrostatically by displacing air in a water tank, the latest models are equipped with a diaphragm pump that provides air at an easily calibrated flow rate (see Chapter 7).
Fig. 1.11. Chopin buret. (Courtesy Chopin Technologies)
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This mode of supplying air pressure eliminates nonuniformity in the airflow rate, a problem that was recognized in earlier reports dealing with the relationships between alveograms and the rheological properties of the doughs (Scott Blair and Potel 1937, Hlynka and Barth 1955). Hibberd and Parker (1974) reported detailed observations of changes in the flow rate depending on the height of the water column in the water tank of the alveograph proper, as well as changes caused by compression of the air trapped between the water and the dough (see Chapter 5). They found significant deviations arising from the decreasing height of water. Nevertheless, they emphasized that such deviations need be considered only in fundamental rheological studies. The deviations seem to be irrelevant when the alveograph is used as an empirical instrument for the routine testing of dough. Besides providing a steady, easily calibrated airflow rate, the air pump offers some other advantages. The water bottle does not need to be raised and lowered. The pump starts to work automatically as soon as the operating lever switch on the alveograph proper is set to position 3, and it is completely automatic on models MA 95 or later. Other improvements in the design and functioning of this new model include the elimination of any clogging of the water pipes and easier checking of internal pressure losses. The dough bubble is created by blowing air underneath the dough patty previously placed on the lower plate (Fig. 1.15). The airflow rate is adjusted by controlling the diaphragm pump intensity and the aperture of a flow meter (the method for adjusting the air rate is detailed in Chapter 7). The effective flow rate is set up at 96 L/hr and is constant throughout the test. The air system (Fig. 1.16) forces air to flow through the opening in the lower brass plate, thereby inflating the dough test piece resting on the plate. The lower plate also is connected to the recording manometer via a tube 110 cm long and 8 mm wide (i.d.) for MA models and 80 cm long and 4 mm wide (i.d.) for the NG. For the MA 82 and MA 87 models (Fig. 1.17), the air passes through a valve that also connects the internal compartment with a pear-shaped rubber bulb having a volume of 18 ± 2 mL. When the operating lever switch is in position 2 and the handle of the air valve is horizontal, the rubber bulb is connected to the internal compartment and the opening in the lower brass plate is open. The air expelled when the rubber bulb is squeezed helps to detach the dough piece from the brass plate before the actual stretching process is started. For MA 95 and NG models, this operation is completely automatic. Following activation of the pump, an electrovalve opens first for 0.675 sec, allowing 18 mL of air to be delivered; then, the second electrovalve opens and the test is performed normally. The alveograph proper also has two isothermal compartments in which the dough pieces are allowed to rest on stainless steel resting plates at 25 ± 0.5°C. The temperature in these compartments is maintained by means of a water reservoir connected to a source of tap water (or a water bath) and a thermostatically controlled heater. The design of the dough clamping device (Fig. 1.17) is nearly identical to that described for the improved model of the Chopin Extensimeter. The Recording Manometer The recording manometer, which experienced very few changes between the MA model (Fig. 1.18) and the NG model (Fig. 1.19), consists of a base supporting a column with a recording drum and a tank. Attached to the manometer tank is another vertical column housing the floating recording pen. The recording drum is connected via a gearbox to a small motor, which starts rotating the drum clockwise as soon as the operating lever switch of the alveograph is in position 3 on the MA 82 and MA 87 models and automatically on NG models. The drum makes a full rotation in exactly 55 sec. If, for any reason, the rotation time deviates more than ± 0.5 sec, the motor should be changed immediately. The position of the manometer in the alveograph NG model is shown in Figure 1.20. The manometer tank holds approximately 75 mL of distilled water and is connected to the open-ended column through two holes. The
Fig. 1.12. Alveograph MA 82.
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top end of the column is used to fill the tank with water (Fig. 1.21). The bottom end empties the column and is sealed with a rubber cap while the instrument is operating. The column has two vertical slots opposite each other through which the horizontal guide bar of the recording pen can move freely and which stabilize the pen in its vertical movement. The pen is attached to a floater that floats in water in the water tank and inside the column above the tank. The water tank is connected to the internal compartment of the alveograph proper. As the pressure from this compartment starts to increase, the pressure changes during dough inflation are recorded over time on a chart placed on the recording drum. Figure 1.18 is an engineering drawing of the recording manometer.
Fig. 1.13. Alveograph MA 87.
The Dough Sheeting Assembly The sheeting assembly supplied with the alveograph (pictured in Chapter 3) is used to prepare dough pieces of a standard geometry. This assembly consists of the following: 1. A stainless steel knife, 60 mm wide, to cut the strip of dough as it is extruded through the extrusion gate of the mixer. 2. One plate with two integrated guide rails 12 Âą 0.1 mm high. The guide rails are placed along the longer sides of the plate and control the thickness of the dough sheet during rolling.
Fig. 1.15. Alveograph lower press.
Fig. 1.14. A, Alveograph NG; B, details of the piston.
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Fig. 1.16. Airflow diagram for the latest model of the alveograph (model NG).
3. A sheeting roller, 40 ± 0.1 mm in diameter and 89 mm long. The diameter of the roller is reduced at each end to 33 ± 0.1 mm. These indented shoulders ride on the guide rails of the assembly. Therefore, a differential of 7 mm presses the dough on the plate and produces a dough sheet 5 mm thick. 4. A circular cutter (46 ± 0.5 mm i.d.) for cutting out dough test pieces from the sheeted dough. 5. Five resting plates for holding the dough test pieces in the resting compartment of the alveograph proper. THE ALVEOLINK CALCULATOR The alveolink (Fig. 1.22) replaces the recording manometer by automatically computing and storing the alveogram indexes P, L, G, W, Ie, and P/L (see Chapter 5 for an explanation of the indexes) as well as the complete curve and all additional data. The test is performed on five dough test pieces prepared and inflated in the same manner as in the standard alveograph procedure. Connected to a personal computer (PC), it allows the user to store all results and keep track of all tests. In addition, the alveolink can store up to 200 tests in its built-in memory. The latest version of the alveolink (model alveolink “I”) allows, within certain limits, an automatic calibration of the complete system, thanks to the use of reference samples. The user performs the tests several times on up to five flour samples with known values. Then the user enters each flour reference value, and the alveolink measures the deviation from the average value obtained for each sample and includes the proper coefficient in its calculations. If the coefficients are too large, the automatic calibration is not applied, and a mechanical calibration by an authorized technician is necessary.
Fig. 1.18. MA model manometer.
Fig. 1.17. Upper brass compartment and the press system of the alveograph proper. Dough bubble (A), upper brass plate (B), piston (C), olive-shaped airflow shutter (D), dough piece (E), brass collar (F), and brass stopper (G). (Courtesy Chopin Technologies)
Fig. 1.19. NG model manometer.
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Fig. 1.20. Position of the manometer in the alveograph NG.
Fig. 1.22. The Chopin Alveolink.
Fig. 1.21. Filling the manometer with distilled water and the floating pen reservoir with ink.
THE ALVEOEXPERT SOFTWARE The Chopin AlveoExpert software (Fig. 1.23) completes the alveograph concept by allowing the use of alveograph results in routine work. It permits the user to do the following: • Store, visualize, and modify alveograph data on the PC, • Compare different flour types (to a reference, for instance), • Create a customized “virtual store” with all materials available, • Realize a traceability curve, • Calculate the best wheat blend to reach a specified quality, • Anticipate the best wheat or flour to purchase in accordance with the material available, and • Enable those using improvers to take into account the quality of the flour tested and the results desired. LITERATURE CITED Bailey, C. H., and Le Vesconte, A. M. 1924. Physical tests of flour quality with the Chopin Extensimeter. Cereal Chem. 1:38.
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Fig. 1.23. The Chopin AlveoExpert.
Chopin, M. 1921. Relations entre les propriétés mécaniques des pâtes de farines et la panification. Bull. Soc. Encour. Ind. Natl. 133:261. Chopin, M. 1927. Determination of baking value of wheat by measure of specific energy of deformation of dough. Cereal Chem. 4:1. Chopin, M. 1935. Pétrin enregistreur et extracteur des pâtes. Meun. Fr. 51:275. Chopin, M. 1937. Nouveaux appareils pour la préparation et l’essai d’extension des pâtes de farines. Bull. Fr. Meun. 60:172. Hankoczy, J. 1920. Apparat fur Kleberverwertung. Z. Gesamte Getreidewes. 12:57. Hibberd, G. E., and Parker, N. S. 1974. The rate of growth of dough bubbles in the Chopin Alveograph. Lebensm. Wiss. Technol. 7:318. Hlynka, I., and Barth, F. W. 1955. Chopin Alveograph studies. I. Dough resistance at constant sample deformation. Cereal Chem. 32:463. Scott Blair, G. W., and Potel, P. 1937. A preliminary study of the physical significance of certain properties measured by the Chopin Extensimeter for testing flour doughs. Cereal Chem. 14:257.