Extensographs

Although the Alveograph measures the same properties as the Bra-bender Extensograph there is no way of converting one set of results into another. Also, unlike the Extensograph, the dough is not kept for a long time. 

Brabender make a whole range of instruments for testing flour. These instruments are the standard ones in use in the UK, Germany and North America. The company has recently produced new versions of these instruments that use electronic measuring systems rather than the mechanical systems previously employed. The new models use the same name but with the suffix E. Thus, the new model Extensograph is the Extensograph-E. 

The Farinograph-E (Figure 6) uses a PC to process the data from the Farinograph this is a considerable improvement over measuring pieces of paper from a chart recorder. The software supplied runs under Windows and can multi-task so that one PC can handle data from several instruments. This is particularly convenient as the Farinograph is used to prepare doughs for the Extensograph. 

Farinograph doughs only contain flour and water, so the water absorption obtained is a theoretical value. The value obtained from the same batch of flour in a bread dough will always be lower. When the Farinograph is used to prepare doughs for the Extensograph, the doughs do contain flour, salt and water. 

The major use of the Farinograph in a bakery laboratory is to prepare doughs for the Extensograph. 

A complete set of measurements from the extensogram will give the energy, i.e. the area under the curve, the resistance to extension, the extensibility and the maximum, i.e. the deflection when the dough broke. The ratio of the extensibility to resistance and the ratio of extensibility to maximum are calculated. The Extensograph-E is set up to calculate these values directly. 

Experienced Extensograph users learn the characteristic shapes of the extensogram typical for flour suitable for particular uses (Figures 9-11). Bread flours need both resistance and some extensibility while in biscuit flours a low resistance and a high extensibility are needed. 

The results of the 1.5- and 3-hour samples give information on the stability of the dough, which is of importance in any long process. Some Extensograph users do not bother with the long-standing times as their products are made by a rapid process. 

The Extensograph is used in several international standards, specifically ICC standard no. 114/1, ISO 5530-2 and AACC standard no. 54-10. These standards are important in the international trade in flour a buying specification written in terms of Extensograph testing to method ISO 5530-2 would not necessarily give the same answers as AACC 54-10. 

Typical Values from the Farinograph and Extensograph. Different sorts of flour might have values such as those shown in Table 2. 

An Example of the use of the Extensograph. The Extensograph is very useful in sorting out problems where several flour samples are successful in an application while others of similar analytical... 

The tests used in cereal labs to measure dough properties are similar to those used in industry to test polymers. For example, the extensograph essentially carries out a tensile stress test. An extensograph measurement differs in fhaf if measures force rather than stress and a constant stretching rate is used instead of a constant strain rate. A tensile stress-strain curve is shown in Figure 6.6. In this test, a sample is strained at a constant rate and the stress needed to maintain this strain rate is measured until the point at which it breaks. The peak stress is the ultimate tensile strength. 

Fig. 15.27. Extensograph (according to Rohrlich and Thomas, 1967). The cylindrical piece of dough (7) is fixed by dough clamps (3) and placed on the balance fork (2). The motor (4) of the stretching unit (5) is then started. The arm moves downward into the dough and extends it at constant speed. Simultaneously, the forces opposing the stretching action are transmitted through the lever system (6) io the balance system (7). This is coupled to a recording arm of the strip chart recorder (8). The fork of the balance system is coupled to an oil damper (9) to reduce the recoil...

A wheat dough is kneaded to the optimum and pressed, rolled or formed after a resting time of, e. g., up to 3 minutes or longer. This dough is subjected to a relatively weak shear compared with kneading. In this case, the resistance to extension is increased in tensile tests in the extensograph (Fig. 15.45). 

Fig. 6. Extensograph analysis of doughs with sourdough and lactic add I and II (different flour typ>e), LAB (biologically acidified dough by addition of sourdough prepared using a starter culture of L. brevis L-75), DS (biologically addified dough by addition of dry sourdough), LA (chemically acidified dough by addition of lactic add).

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