Experimental cookery

Shortening. Two teaspoons per pound loaf produced good results but Davis and Cline have found that increasing the fat to 1 or 1^^ tablespoons gives an increased volume and sheen but also requires a longer fermen- tation. The staling o£ bread. Aside from the organoleptic means of detect- ing staling, several methods have been used by investigators. Karacsonyi has reported the use of the viscosimeter for this purpose. Piatt summarizes these methods and reviews the literature on staling. When soaked in an excess of water stale bread does not swell to the extent that fresh bread does. When viewed with the microscope the starch granules in stale bread have a more distinct outline, and often an air space occurs between the starch and gluten. The water extract from fresh bread contains more THE STALING OF BREAD 437 soluble starch products than that from stale bread. Fresh bread is more elastic than stale bread, hence measuring the compressibility is also a means of determining the degree of staling. Staling includes all the changes taking place during the storage of bread, cake, pastry, etc. These changes include volatile losses, changes that may be due to oxidation, and most important, changes that occur within the product, which Piatt terms "inherent staling." The volatile losses are largely composed of water, but include small amounts of carbon dioxide, alcohol, acetic acid, diacetyl, and other sub- stances, all of which give the distinctive aroma to fresh bread. The moisture loss can be largely prevented. Stale crackers, fruit cake, and other products often deteriorate in flavor because of the oxidation of the fats they contain. Even if moisture loss is prevented from a loaf of bread certain changes take place within the loaf which give it a flinty feel and a crumbly texture. Colloidal systems change slowly and temperature may have a decided effect on the change. In baking, as the gelatinization temperature of the starch is reached, the starch swells, absorbing whatever moisture it can obtain; but the gluten may lose moisture. However, as the bread cools part of the starch is precipitated and releases moisture, which may be absorbed by the gluten or become the source of the dampness of wrapped cool bread. The staling process is reversible, i.e., the stale bread when heated again to a high temperature acquires the characteristics of fresh bread. This reversal can be repeated several times or until the bread has lost too large a proportion of moisture. Though both starch and protein play a role in staling, more work has been done in studying the part starch plays than that of the protein. Not all the starch is gelatinized in baking, so that the freshly baked bread is not entirely transparent, but has more of a transparent appearance than stale bread. Bryant has reported the following percentage of soluble extract in one experiment: for dry flour after mixing 9.32 per cent, after proofing 10.52 per cent, 30 minutes after baking 13.82 per cent, 6 hours after baking 13.46 per cent, 24 hours after baking 11.92 per cent, and 70 hours after baking 10.41 per cent. He adds that the effect of fat in bread in preventing staleness is not known, but that salt is supposed to tend to increase the staling in that starch changes more rapidly to insoluble starch if salt is present.