a1 Reader in Agricultural Chemistry in the University of Cambridge.
Attention is drawn to the complexity of the ideas comprised in the term strength as applied to flour, and the necessity of investigating each idea separately.
The chemical composition of the gliadin and glutenin of strong and weak flours has been investigated, and it is shown that they are identical in all the flours examined. It is suggested therefore that the difference between strong and weak flours is connected rather with the physical properties of their gluten than with the chemical composition. Since it is well known that the physical properties of proteids are profoundly affected by small quantities of acids, alkalis, and salts, the amounts of these substances in strong and weak flours were determined. In the few cases examined, it was found that strength was associated with a high ratio of proteid to salts, and weakness with a low ratio. It is suggested that the variation of this ratio may be the explanation of the different physical behaviour of the gluten of strong and weak flours, and that this is the factor which determines that component of strength which governs the shape of the loaf, and its power of retaining gas. This point is receiving further investigation.
The factor which primarily determines the size of the loaf which a flour can make is quite distinct. The size of the loaf is shown to depend in the first instance on the amount of sugar contained in the flour together with that formed in the dough by diastatic action. It is proposed to measure this by incubating the flour with yeast and water, and collecting the carbon dioxide evolved during 24 hours. Particular attention should be paid to the rate of gas evolution in the later stages of the fermentation, as this is shown to be more directly connected with the size of the loaf.
Taking Humphries and Biffen's definition of strength as “the capacity for making large well-piled loaves,” and applying the above ideas, it is stated that the largeness of the loaf depends chiefly on the capacity of the flour to give off gas when fermented with yeast, especially in the later stages of dough fermentation, and the suggestion is made that shapeliness, and probably gas retention, are dependent on the physical properties of the gluten as modified by the presence of varying proportions of salts.