120 



♦ KNOWLEDGE ♦ 



[Aug. 24, 1883. 



the mill has been worked for a short time, it becomes 

 necessary to " dress " or re-cut these lines on the surface of 

 the millstone. This operation requires a considerable 

 amount of skill, and is performed by means of a heavy 

 hammer with a chisel cutting edye, set at right angles to 

 the hilt (something like certain makes of geological 

 hammers). Blow r-fter blow is struck with this implement 

 until the line is sutKciently deepened and a good cutting- 

 edge is produced. There are usually about eight or ten of 

 these lines to the inch. It will be readily understood that 

 a single false blow may undo a lot of careful work by de- 

 stroying or damaging one of the.se delicate ridges. At 

 present, in many large mills the stones are dressed by 

 machinery. The cutter consists of a small steel wheel with 

 a number of little diamonds embedded in its circumference. 

 The machine provides for the rapid revolution of this cutter 

 at the same time that it is drawn along the surface of the 

 stone in the direction in which the line lines run. The 

 diamonds thus dress the stone with remarkable speed and 

 accuracy. 



The Hour as it leaves the stone is termed " whole meal " ; 

 it contains the starch, itc, Ln the form of very fine particles, 

 while the husk of the grain is simply cut into fragments of 

 sensible size, which in the case of wheaf^flour constitute the 

 bran. Brown bread is either made from whole meal or 

 from white flour to which bran has been added. Most 

 people prefer, as a staple article of consumption, bread 

 made from flour deprived of its bran. The miller removes 

 this material by passing the flour through a number of 

 sieves of varying degrees of fineness ; in this way the husk 

 is separated in different degrees of coarseness ; " braii," 

 "pollard," and "sharps" are names given to three grades 

 of the separated husk — bran being the coarsest, and sharps 

 the finest of the fhree. 



The bran and the white flour produced from the interior 

 of the grain differ considerably in composition, there being 

 much more nitrogenous matter in the former than in the 

 latter, which, on the other hand, contains a much higher 

 percentage of starch. We have here a most important 

 question to consider, because the nutritive value of bread 

 must depend largely on its composition. Speaking gene- 

 rally, we may divide food-stufTs into two groups — first, the 

 nitrogenous or flesh-forming substances, termed by the 

 physiologist "proteids," and, second, the non nitrogenous 

 or fat-forming and heat-producing substances. The nitro- 

 genous food-stufis are also eflicient as maintainers of 

 animal heat. It is necessary for the healthy continuance 

 of life that both nitrogenous and non - nitrogenous 

 articles of food be eaten. Animals fed exclusively 

 on non-nitrogenous diet speedily emaciate and die ; life 

 is, however, much more prolonged in those entirely fed 

 with nitrogenous food. The value of bread as an article 

 of food is greater the more nitrogenous matter it contains, 

 provided the nitrogenous matter is of such a nature as to 

 be readily assimilated by the .stomach. From time to time 

 the use of whole-meal bread has been urgently ad-\ ocated 

 on the score of its greater nutritive power ; but the larger 

 proportion of nitrogenous matter it contains is largely 

 compensated by its being practically insoluble. The bran 

 of whole-meal bread is found to be discharged from the 

 system in an almost unchanged condition. From its pro- 

 ducing a mechanical irritation of the inner surface of tlie 

 intestine, it often acts beneficially in cases of chronic con- 

 stipation. 



Dealing first with white flour, a momentary reference 

 may be made in passing to other methods of cooking it than 

 making bread. Dmnplings, suet-puddings, &c., consist 

 essentially of flour mi.xed with suet or other fat, kneaded 

 with water into dough, and subsequently boiled. The 



chemical changes thus produced are very^^slight, the prin 

 cipa) one being the gelatinising of the starch. 



The simplest form of bread is the ship-biscuit, or " hard 

 bread " of the sailor. To make these biscuits, flour with a 

 little salt is kneaded with water into a stiff dough. This 

 is rolled into a thin sheet and cut into biscuits, which are at 

 once rapidly baked in an oven. Although hard, ship-biscuits 

 of good quality have an agreeable flavour, and when soaked 

 in hot coffee and then buttered, form an appetising dish. 

 Bread of this kind is particularly valuable for sea-going 

 purposes, because it may be kept in a dry place for almost 

 an indefinite length of time without undergoing any 

 change. 



It would be difficult to persuade many landsmen that 

 ship-biscuit at all deserves the name of bread. Perhaps 

 with the sailor, who invariably so terms it except when 

 he uses the phrase " hard tack, ' the wish is father to the 

 thought. Biscuits, whether ship or otherwise, certainly do 

 not fall within our ordinary definition of bread, which may 

 be described as the flour of wheat or other grain made into 

 a paste with water, then rendered porous by being 

 charged with carbon dioxide gas (formerly termed car- 

 bonic acid gas), and next baked by the heat of an oven 

 into loaves with a light brown crust and porous interior. 



The first step in bread-making is to secure some means 

 of causing the dough to rise, that is to render it porous by 

 the production within it of gaseous carbon dioxide. It 

 has been already explained how the gluten in wheat flour 

 enables it to produce a highly elastic dough, and thus to 

 retain the vesicular structure resulting from the generation 

 within it of gaseous Vjubbles. It is here that our know- 

 ledge of the constituents of grains becomes useful. If 

 moist flour be exposed to the air, the nitrogenous matter 

 quickly passes into a state of decomposition, and acquires 

 the power of rapidly changing the starch of flour 

 not only into dextrin and sugar, -but still further into 

 carbon dioxide and alcohol. This second change is termed 

 " fermentation," and is now definitely ascertained to depend 

 on the presence and growth of certain living organisms in 

 the moistened mass. The sporules or seeds of these bodies 

 are floating about in the air, and dropping on to the 

 moistened flour, develop and multiply, and effect this 

 remarkable decomposition of sugar. Although fermenta- 

 tion plays so important a part in the making of bread, yet 

 it is a far more important element in the production of 

 beer and other liquors from malt. When dealing with 

 them, fermentation can best be considered and explained. 

 The moist flour which has acquired this property is termed 

 " leaven," and, when added to a larger quantity of dough, 

 causes fermentation of the whole mass. The carbon dioxide 

 distends the dough by the production of bubbles, the 

 alcohol is evaporated off during the baking of the bread. 

 The production of alcohol and carbon dioxide by the de- 

 composition of sugar is shown by the following equation : — 

 C,;H„0, = i!C,H„0 + 2C0., 

 Sugar. Alcohol. Carbon Dioxide. 



Our next article will continue to deal with the chemistry 

 of bread-making. 



We are glad to be able to announce that after three 

 weeks of enforced rest the editor of Knowlediie hopes to 

 begin lecturing again (at Eastbourne and Hawkhurst) next 

 week, not at once returning to full work, but hoping 

 gradually to resume his usual working habits. He begs 

 that correspondents will bear with him if there have been 

 delays or omissions. Like the man of whom Mark Twain's 

 correspondent wrote so touchingly, he has " done his level 

 best." 



