The superiority of yeast bread became gradually visible to all, the decisions of the medical faculty were forgotten, and the prohibition laws were allowed tacitly to sink into oblivion. The new mode of baking by degrees extended itself to other countries, and is now, we believe, practised everywhere. In warm climates, where the yeast of beer cannot be had, other substitutes are employed, which answer the same purpose. In the East Indies, bread is raised by means of the liquor called toddy, which flows out of the cocoa-nut tree when its branches are cut, and which ferments so rapidly, that in two or three hours it becomes an intoxicating liquor. In the West Indies dander is employed for the same purpose. This is the liquid which remains in the still after the rum is distilled off, and is therefore analogous to what our distillers call spent wash. It no doubt consists of a solution of unaltered sugar, prevented from fermenting by the alcohol which the liquid contained before distillation, and mixed doubt less with a quantity of yeast. In that warm climate it undergoes a very speedy fermentation, and on that account answers all the purposes of yeast in the baking of bread. In this country it is no uncommon thing to convert the spent wash into small beer, which the workmen drink with avidity. But it only undergoes this change when fermented in the usual way with yeast.
8. The appearance of wheat flour is too familiar, to every person to require any description here. The ancients knew that it consisted chiefly of a substance called starch ; which, as Pliny informs us, was first separated from wheat by the inhabitants of the Island of Chio, and in his time the starch of Chio was con sidered the best and lightest, because it was made from wheat which was not ground. .(Plinii Natur. -Hid. 18. 7.) This is the mode still followed by the manufacturers of starch, sand is no doubt the reason why the other constituents of wheat were so long in being discovered. About the year 1728 Beccaria, an Italian philosopher, discovered another constitu ent of wheat, to which the name of gluten has been given. His method of obtaining it was this : He took a quantity of flour, and formed it into dough with water ; _this dough he kneaded continually be tween his fingers, while a small stream of water dropt upon it. He continued the kneading as long as the water ran off milky. By this process, the whole of the starch was washed away, and there remained in his hand a grey-coloured, elastic, and very adhesive substance, which was the gluten. (Collect. Academ. pantie Etrang. 10. 1.) No other grain, besides wheat, contains gluten in any considerable quantity. Traces of it may be discovered in barley. But the gluten of barley cannot be separated by washing. It is obtain ed by solution in water. For gluten is soluble in a small proportion in cold water. But when that liquid is heated to'120° or 130° the gluten coagulates, and falls down in grey-coloured flocka. By this method gluten may likewise be discovered in the leaves of many trees.
The water employed to wash out the starch soon deposites that substance in the form of a white pow der. if this water be now filtered, evaporated to a small quantity, filtered again to separate the coagu lated gluten, clarified with white of egg, and then evaporated to the consistence of a syrup, it deposites, as we them a sufficient quantity of gluten, or mix them with wheat flour. In this way barley,
potatoes, and even turnips, may be made into very good bread.
11. The sugar is by far the smallest, in proportion, of all the constituents of wheat flour. If it be starch sugar, as we believe it to be, it possesses the following properties: It does not crystallize in prisms like common sugar, but assumes the form of spheres like honey. It is not so hard as common sugar, nei ther is it so soluble in water. Its sweetening power, according to Kirchhoff, is to that of common sugar as 1 to 2i. But the most distinguishing property is that, when dissolved in water, it ferments of itself, without the addition of any yeast ; whereas common sugar does not undergo that process unless yeast be mixed with its aqueous solution. Hence the reason why the dough of wheat flour ferments, and is con verted into leaven. This fermentation does not take place if the saccharine matter be washed out of it by water, as Mr Edlin ascertained by direct experiment. The fermentation of wheat flour is confined to the saccharine matter. It first undergoes the vi nous fermentation ; here the process, if possible, ought to be stopped. But as this is usually not pos sible, the acetous fermentation commences, and vine gar is formed. Probably at last the starch itself is acted on, and occasions the bad taste of ill baked lea vened bread, though this is doubtful.
12. As to the proportions of these three constitu ents, they differ so much in different kinds of wheat flour, that nothing precise on the subject can be de termined. The greater the proportion of gluten, the better in all cases is the flour. When the wheat has not fully ripened, or when it has been exposed to rain while lying on the field, the gluten cannot easily be separated from the starch by the process above described ; nor does it form an elastic, adhe sive mass ; but a friable substance, distantly resem bling the fibrous matter of potatoes. Hence the goodness of the flour may be determined by the state of the gluten. The writer of this article has repeat edly applied this test to London flour; but he has been always unlucky enough to find it decidedly bad. From the flour furnished by two or three differ ent bakers in different parts of the town, he either was unable to obtain any gluten, or it wanted the ad hesiveness which characterizes the gluten of good wheat. No doubt, there must be abundance of excel lent flour in London ; but we believe (and our opinion is founded on the bread, which, in general, is greatly inferior in goodness to the Edinburgh bread) that.a very considerable proportion of the flour used is bad. The inhabitants of London pride themselves on the goodness of their bread ; but never was any set of men more mistaken. The London bread is, indeed, whiter; but, in other respects, worse than any we have met with in Great Britain, except the bread baked in Berwick-upon-Tweed, which is very bad, owing entirely to the unskilfulness of the bakers.