Rheology of foodstuffs.

It would clearly be pointless in this lecture either to attempt to list all the papers that have been published on a vast variety of foodstuffs, nor even selecting only a fcw, to describe in detail to a Budapest audience, the apparatus that is commonly used for testing a few of the principal products that have been intensively studied. Under Professor TELEGDy-Kov~.(Ts, pioneer work has been and is being done here in this field. What will be attempted will he to suggest the fundamental reasons for doing such tests and to propose some sort of classification of the kind of tests that can profitably be done. Why are rheological tests on foodstuffs done at all? For three principal reasons: (1) to ensure that raw materials are suitable for processing. For example, wheat grains that are too hard or too soft willuot mill properly. (In this connection, I am especially happy to read of a recent agreement between my country and Hungary on co-operation in the study of this problem). (2) It is often necessary to test intermediate products. Again taking hread-making as an example, the rheological properties of a flour-dough are clearly very important in defining the quality of the loaf that can be made from it. (3) Finally, we have the finished product. Here one is generally concerned with the reaction of the consumer. This differs widely in different countries and at different times. Thus the French seldom spread jam on their bread and are therefore much more interested in flavollr than in the texture, especially the size of the holes. As a young man, I was sent to Franee to study what differences in the rheological properties of the doughs are correlated with the different textures required in France and in Britain to produce the sort of bread which is wanted in each country. Three types of test can he done. The first attempts to make standard test-pieces and to subject them to simple stresses or strains, so as to measure "physical properties" (as described in the earlier lecture) or at least properties changing in a more or less controlled manner during the tests. Such tests are not aI-ways appreciated hy the man in the factory hut they can he valuable because they make it possible to link rheological properties with, for example, chemical constitution. Much work (which will be briefly descrihed in a moment)