the same with yest. See YEST.—Barm is said to have been first used by the Celts in the composition of bread. About the time of Agricola's entrance into Lancashire, a new sort of loaf had been introduced at Rome; which was formed only of water and flour, and much esteemed for its lightness; and it was called the water cake from its simple composition, and the Parthian roll from its original inventors. But even this was not comparable to the French or Spanish bread for its lightness. The use of curmi, and the knowledge of brewing, had acquainted the Celts with an ingredient for their bread, which was much better calculated to render it light and pleasant, than the leaven, the eggs, the milk, or the wine and honey, of other nations. This was the spume which arose on the surface of their curmi in fermentation, and which the Welch denominate burn and we barm. The Celts of Gaul, of Spain, and most probably therefore of South-Britain, had long used it; and their bread was, in consequence of this, superior in lightness to that of any other nation in the world. See the articles BAKING and BREAD.