Page:Encyclopædia Britannica, Ninth Edition, v. 3.djvu/270

beginning of the process being from 550 to G00 Fahr. The baker can ascertain if the oven is at a proper tem perature by throwing a little flour on the sole of the oven, which ought to turn to a light brown colour. Ovens in London are usually built of brick, with a sole only 2| inches thick ; in Scotland stone is used, the sole being from 10 to 12 inches thick, and the oven consequently

retains heat much more effectually.

In Scotland the system of using ferments is not gener ally practised as in London, some of the varieties of yeast or barm being mixed directly with the flour. In some localities the system of setting " quarter sponge" is adopted, in which the sponge originally prepared contains only one- fourth of the flour to be used. To this, after an interval of about twelve hours, more flour and water are added, which brings it up to half sponge, and about two hours thereafter the mass is ready for making the dough. In Paris, where bread-making is carried to the highest perfection, leaven, as has already been mentioned, is the fermenting agent employed. This consists of a portion of dough laid aside from a previous baking in a uniform temperature for seven or eight hours, during which it swells and acquires an alcoholic odour. This, termed " the chief leaven," is taken and worked up with flour and water to a firm paste double its original mass, when it becomes " the first leaven." After an interval of six hours the amount is again doubled, forming the second leaven. The " complete leaven " is formed by doubling the size of the second leaven, and the proportion the complete leaven bears to the finished dough is about one-third in summer and one-half in winter. Sound flour yields from 90 to 94 4-lb loaves per bag of 280 Ib, some "strong" flours giving even a greater quantity of bread. A table of experiments, conducted by Messrs Lawes and Gilbert, gives a mean result of 135 - 2 of bread from 100 of flour; and in the observations of a large number of English and French authorities quoted by them, the ratio of bread to 100 of flour varied from 127 to 150. The following table gives the mean of 25 analyses of the bread of London bakers by Dr Odling:—

Water 43 43 Organic matter 55 - 26 Mineral matter or ash 1 - 30 Percentage of ash in dry bread 2 30 nitrogen in new bread 1 26 ,, ,, in dry bread 2 22 The bakers standard of excellence of flour, apart from the question of colour, is the weight of bread it will pro duce of a proper dry ness and texture. The " strength " of flour in this respect appears to depend much more on its condition than on the absolute percentage of its constituents. Panary Fermentation.—It would be altogether out of place in this paper to refer to the conflicting theories as to the cause of fermentation in organic substances. The so- called panary fermentation in bread-making is a true alco holic fermentation, and whether induced by" yeast or leaven the result is precisely the same. The gluten of the flour is the fermenting agent, and it is stirred into activity by contact with a glutinous body already in an active condi tion, which may be either yeast or leaven. In this con dition it exerts a fermentative influence over the sugar which may either have existed previously in flour, ^or which is at least immediately developed in it by the influ ence of moisture. The active gluten splits up each mole cule of sugar into two of alcohol, two of carbonic acid, and one of water, and consequently an infinite number of minute air bubbles are developed throughout the ferment ing mass. The reaction is shown in the follow-in^ equa tion : C 6 H. 4 7 = 2(XH 6 + 2CO, + H 2 0.

Carb. Hyd. Oxy. Carb. Hyd. Oxy. 1 molecule of Grape Sugar 6 14: 7 2 molecules of Alcohol 4 12 2 2 ,, Carbonic Acid 2 ... 4 1 Water 2 1 . 6 14 7 As the evolution of carbonic acid and alcohol proceeds, the sponge gradually swells, the little bubbles coalesce and enlarge, rising through the tenacious mass till the surface is reached, and then the carbonic acid bursts out and the dough begins to fall. This process would go on a consider able time, but the alcoholic fermentation would soon pass into an acetous fermentation and the sponge would become sour. When acetous fermentation ensues, as not un- frequently happens in baking, it may be remedied to some extent by the addition of bicarbonate of soda to the sponge. The late master of the mint, Dr Thomas Graham, was the first to demonstrate the presence of alcohol in fermented dough, and he thus described his experiment: "To avoid the use of yeast, which might introduce alcohol, a small quantity of flour was kneaded, and allowed to ferment in the usual way to serve as leaven. By means of the leaven a considerable quantity of flour was fermented, and when the fermentation had arrived at the proper point, formed into a loaf. The loaf was carefully enclosed in a distilla tory apparatus, and subjected for a considerable time to the baking temperature. Upon examining the distilled liquid, the taste and smell of alcohol were quite perceptible, and by repeatedly rectifying it, a small quantity of alcohol was obtained, of strength sufficient to burn and to ignite gun powder by its combustion. The experiment was frequently repeated, and in different bakings the amount of the spirit obtained of the above strength was found to vary from 3 to 1 per cent, of the flour employed." Although the tem perature of the oven drives off that amount of the spirit, fermented bread is yet found to retain a proportion of alco hol, as much as from 221 to 401 per cent, having been found in different specimens of baked bread. Speaking in 1858, Dr Odling estimated the amount of alcohol thrown out into the atmosphere from the bread baked in London as equal to 300,000 gallons of spirits annually. Many years ago a patent was secured by a Mr Hicks for collect ing and condensing the alcoholic fumes from bakers ovens, and a company was formed for working the invention. After an expenditure of 20,000 the attempt had to be abandoned, not from any failure to obtain the spirit, but because the bread baked in the process was dry, unpalat able, and unsaleable.

When what is termed " whole wheaten flour "that is,

the entire substance of the grain, excepting only the outer bran is baked, it is known that the resulting loaf is of a dark brown colour, sweetish in taste, and liable to be some what heavy and sodden. The brown colour was at one time supposed to be due to the presence of bran particles in the flour, and in 184G an American, Mr Bentz, invented a process for removing the outer cuticle of wheat before grinding, it being supposed that the flour so prepared would yield a loaf of white colour, while utilising a larger proportion of the substance of the grain than is commonly used. To the astonishment of experimenters, however, the bread made from such flour was found to have the colour and other characteristics of whole wheaten bread. The subject was investigated by an eminent French chemist, M. Mege Mouries, who found that the peculiar action of whole wheaten flour was due to the presence in the outer part of the seed of a peculiar nitrogenous body, to which he gave the name cerealin, and which is closely allied in composition and action to the diastase of malt. Cerealin exerts a peculiarly energetic influence on starch, transform ing it into a brown adhesive mixture of dextrin and sugar.

He showed that when the fermentative action of gluten