Who first conceived the idea of using yeast or leaven, or making bread by any process of fermentation, or at what period it was first so made, we do not learn. We know that the Israelites made leavened bread; so did the Egyptians and Grecians; but who first invented yeast or leaven? The Romans, it is thought, learned the art of bread-making, with many other valuable lessons, during their war with Perseus, king of Macedon. On the return of their armies from these wars, they brought Grecian bakers with them into Italy. This was two hundred years before the Christian era. Bakers were highly esteemed, and during the reign of Augustus there were three hundred and twenty-nine public bake-houses in Rome, chiefly under the management of Greeks, who were for many years the only ones who could make good bread. They enjoyed many privileges, and were put in charge of the public granaries. The making of fermented bread then gradually found its way into Gaul; but it was a long time before it was known in Northern Europe. In the middle of the sixteenth century, unfermented cakes were the only bread known in Sweden or Norway. It was not till near the end of the sixteenth century that the use of yeast was much known in Northern Europe. About that period yeast from Flanders was brought into Paris as a substitute for leaven. This change greatly improved the bread; but in 1688 the College of Physicians declared that bread made from yeast was very injurious, and the government forbade its being used. But the shrewd Flemish people put up yeast in sacks to allow the liquid part to filter through, and privately sent it to Paris. The excellence of the bread thus made became so evident, that the College of Physicians and their wisdom were forgotten, and the government’s prohibition quietly allowed to sink into oblivion. Very soon this new and improved method of preparing bread extended into other countries. Leaven is flour and water mixed to a paste and set in a warm place--from 70° to 80°--till it ferments, first passing into the vinous and then to the acetous state. Bread made from leaven differs from that made from yeast by almost always having an acid taste. A piece of dough, from well-raised bread, set aside on ice or in a cool place, and worked into the next batch to be made, gives the best mode of making leaven; and by working a little soda into it before setting the sponge, will make very fine bread, without the acidity common to leavened bread, if managed with care.