Friday, January 12, 2007

Friday Library: Science of Cooking, 2

Belle Lowe, Experimental Cookery
1st edition, 1932; Wiley

First part: Emulsions.

Wheat Flour and Bread

Wheat-germ-&-glutenThe protein particles in the flour may be compared to chewing gum, for many of the properties are similar... The behavior of the protein particles when moistened is similar to that of the gum. When first moistened they are crumbly and do not adhere together. After the particles become hydrated they become sticky and tenacious.

gluten2Gluten forms a continuous phase in dough. The protein in the dough forms a continuous network or mesh structure throughout the dough. In this meshwork are the starch granules, the sugar, salts, and water.

The protein particles compose only a portion of the flour content, although after they are hydrated the relative volume that they occupy in the dough is greater than their volume in the flour. If to the chewing gum we add some small round particles… [they] will tend to keep the pieces of gum apart, so that manipulation and sliding over the round particles is required to bring different surfaces of the gum in contact with each other.

gluten...A good quality of gluten must be elastic enough to stretch around the starch granules, and in addition stretch and retain gas bubbles formed in the dough that make the structure porous. No dough will retain all the gas formed within it, but a gluten of good quality will retain a very large portion of the gas bubbles.... Strong glutens may be improved by the addition of malt extract, which contains a larger proportion of the proteolytic enzyme protease than is found in the flour. Since part of the protein is hydrolyzed by the protease there is not such a compact mass left and the remaining gluten is softer and more elastic.


Effect of mechanical treatment on extensibility of dough. Bailey and Le Vesconte have reported that prolonged mixing may destroy the cohesiveness of the gluten... The most extended experiments on the mechanical modification of gluten quality that have been reported are those of Swanson and Working. They devised a machine with a ‘pack-squeeze-pull-tear fashion.’ By mixing the dough for a longer time in this bread mixer they found that the bread could be baked at the end of the first fermentation period, thus decidedly shortening the total time for fermentation... ‘The figures for volume, color and texture show a progressive improvement with the length of time of mixing.’ Dough mixed for 15 minutes produced a loaf better in every way than a loaf mixed for 3 minutes and then fermented in the usual way.... Swanson states that... dough must not be squeezed too hard when kneaded just before it is put into the pan... If kneaded too hard just before being put in the pan these [meshwork of gluten] filaments are packed together and as a result a thicker cell wall is produced.

... Applying these results it can be stated that the first mixing and kneading, when the gluten is developed, should be thorough, but may not need heavy pressure, and the second and third kneading should be done with light pressure and should not be continued for too long a period...
The bowl that the dough is allowed to rise in should have only a thin film of fat... Heavy greasing may produce streaks in the bread... Harrel found that bread baked in ungreased pans gave a better volume and oven spring than bread baked in greased pans.

The staling of bread. ... 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. These are due to changes occurring in the starch and protein of the bread. In baking, the bread reaches a high temperature, and upon cooling these two systems are not in equilibrium. The staling process is reversible, i.e., the stale bread when heated again to a high temperature acquires the characteristics of fresh bread....

If the bread is kept at a temperature of 60 C or above, and if moisture loss and condensation of water are prevented, the bread stays fresh indefinitely.
[Ed: Though it will probably grow Gooey Things.] Thus staling is brought about by cooling of the bread.... at about 40 C [bread] becomes approximately half stale, at 30 C it becomes still more stale, and at 17 to 0 C it becomes totally stale. But although at 0 C bread stales quickly, more intense cold inhibits staling.