1.4.7. Rheofermentometer and
Texture Analyzer
Baked volume and the characteristics of the crumb are the two most
important quality attributes of baked products. Both are determined by the
choice of raw materials (wheat, flour, yeast, other ingredients, additives etc.)
and influenced by technical measures and can be demonstrated for the entire
chain of production in the individual phases, starting with the raw material
flour, through the dough processes and finally in the crumb as the end product.
Since we are dealing with physical properties of the substances it is possible
and appropriate to determine the characteristics of the raw materials by
rheometric methods and observe the effects of the technical measures and
treatments used. Food rheometry offers a number of measuring instruments that
differ greatly in respect of their efficiency, the information they provide and not least their acquisition and running costs. The measuring
instruments of applied and fundamental rheology most in demand are those that
are simple to use, have a good price-to-performance ratio and are suitable for measuring
various different materials.
Rheofermentometer
The Rheofermentometer (Tripette et Renaud/ Chopin, Villeneuve la
Garenne, France) is an instrument that measures the interaction of gas
production and gas retention in wheat doughs from a practical point of view. Maximum
CO2 formation and the moment at which gas is released from the dough during fermentation
can be read off from a gas formation curve, and the ratio of the amount of gas
retained to the overall amount of gas can be calculated. Corresponding to this,
a curve for the height of the dough is recorded; it shows the maximum height
and the stability of the dough (before the CO2 is released), also during
fermentation. A simultaneous analysis of the two curves reveals the
fermentation properties of a yeast and a dough under given conditions and permits
conclusions with regard to the characteristics of the raw materials (various
flours, yeasts, sugar) and the measures that have to be taken to optimize the
production process. This viewpoint distinguishes the Rheofermentometer from the
Brabender Fermentograph and the Maturograph. The Rheofermentometer has been
used throughout the world to investigate the gas retention capacity of
different qualities of the raw material flour (flour grinds, wheat varieties,
sprout) and their reaction to the addition of dried gluten and ascorbic acid,
and also to study the effect of maltose and other sugars (sucrose, lactose) and
α-amylase on the development of the gas. Some ingredients such as carboxymethyl
cellulose have also been known to cause changes in both gas retention and gas
formation capacity. Special attention is given to the effects of the dairy products
low-fat and full-cream dried milk, whey and caseinate; being surface-active substances,
these have an enormous effect on baked volume. These investigations have helped
to optimize the formulations of such products. Tests with the Rheofermentometer
have shown that the fall in baked volume caused by the storage of frozen dough
portions is caused not by reduced gas retention but solely by reduced gas
formation capacity. This has also been taken into account when optimizing
formulations (ingredients, speed of freezing).
The Rheofermentometer has therefore shown itself to be a useful
instrument in practical baking. To answer specific questions the measuring
program suggested by the manufacturer of the equipment can and must be altered.
Maturograph and Oven-Rise
Instrument
For some time the gas formation and gas retention capacity of a dough
made with yeast has been measured with a combination of two rheometric devices,
the Brabender Maturograph and the Oven-Rise Instrument. The Maturograph records
the change in volume of a dough fermenting with yeast by tracing the shape of the dough specimen with and without pressure; in this way
it determines both the viscoelastic properties of the dough and the time of
greatest activity of the yeast or the end point of fermentation. At this time a
sample of dough from the same batch is "baked" in oil heated to a
controlled temperature, and the oven rise of the yeast is described under
conditions similar to those of an oven by recording the amount of rise or the
loss in weight of the sample. These two methods form a bridge between the cold
phase of the dough in the fermentation chamber and the hot baking phase in the
oven in the form of a recording laboratory test without the need for a baker's
oven or a direct baking trial.
The two devices can be used successfully and helpfully for practical
and scientific purposes in cereal laboratories. They make it possible to examine
a number of raw materials (wheat, flour, yeast), to optimize flour blends and methods
of flour improvement, to develop, make up and test ready-mixed flours for
special products, and ultimately to adjust flour qualities to the existing
production process or the production process to existing flour qualities. Inclusion
of the Do-Corder, a recording mixer with adjustable mixing intensity, in the
measuring procedure with the Maturograph and Oven-Rise Instrument to make up
the DMO (Do-Corder-Maturograph-Oven Rise) System has complemented and greatly
consolidated the information yielded by the test. The system also describes the
behaviour of the dough as a reaction to intensive mechanical stress and recognizes
the mixing requirements and kneading tolerance of the dough. The introduction
of the DMO System has finally enabled a more complete description of the suitability
of flours for various different baking purposes (Seibel and Cromentoyn, 1964; Brabender 1965, Brabender and Schäfer 1971, Schrader 1984).
Texture Analyzer
The Texture Analyzer (Stable Micro Systems, Goldalming, England) is a
universal instrument that justifies its popularity in two respects. It works on
the principle of a compression and tension measuring device with a range of different
tools. Universal instruments of this kind, with the same measuring principle,
have existed for a long time. But because of its size and ease of
operation, this device is also suitable for cereal laboratories. On the one hand
its versatility enables the user to make simple, quick and objective
measurements of viscosity with materials of different consistencies and structures
such as whipped cream, mustard, ketchup, starch gel and also wet gluten, dough,
and the crumb of baked products. It is even possible to measure the fracture strength
of crispbread and biscuits. On the other hand, a feature of the universal
nature of the instrument is that the free choice of loads makes it possible to
describe the flow properties of a substance in the sense of fundamental rheometry.
Being a tensile instrument it is similar to a Mini-Extensograph that
can record the structures (viscoelastic properties) of the wet gluten and the
dough strands by measuring their extension (using a small sample and the
Kieffer rig). This makes it possible to describe both the quality of the wheat
or flour as raw materials and the effect of the additives and ingredients on
the properties of the dough. Used in the compression mode the instrument simulates
the baker's finger, and by penetrating the specimen (depth of penetration as a
function of the force applied and time) it ascertains the viscosity of the
dough (and thus its water absorption) (Tscheuschner and Auermann, 1964) and
also the crumb characteristics of the finished bread. Compression of a sample of bread crumb defined in
terms of geometric dimensions makes it possible to record and describe the texture
of the sample even more precisely and reliably – useful for describing the chewiness
and staling of the crumb. Similarly, a suitable measuring technique can be used
to describe the cooking properties of pasta. Further measuring cells have
recently been developed that make it possible to measure the
"stickiness" of a surface (dough, bread crumb, pasta, rice) and state
it in terms of numbers, or to describe the characteristics of dough by means of
biaxial stretching, as for the Alveograph (Dobraszcyk, 2002).
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