An old word the name for the thick froth, produced in brewers vats and sold for bread-making purposes, and for brewing home-brewed ales, ginger beer and treacle beer. In the trial of the Earl of Somerset for high treason and for the murder of Sir Thomas Overbury, in the reign of James I, the arraigning council, Sir Francis Bacon , mention barm, or yeast, as an agent for poisoning. “As we may see in the example of Henry VIII, that where the purpose was to poison one man, there was poison put in the barm or yeast; and with the barm, pottage or gruel was made, whereby sixteen of the Bishop of Rochester‘s servants were poisoned”. This the word barm, with a precise, if sinister meaning and association, was in use over 300 years ago. The term is used in country districts as meaning brewer’s yeast, and in some parts is even applied to pressed yeast.
But since bakers, or others for them, began to make a fermenting agent for themselves, about 1800, that has been described as bar, while the word yeast has been retained for the brewery product, as well for the more modern article sold in more solid form. Barm contains yeast cells, generally as a variety of species, as well as some of the liquor in which the yeast has been grown. Barms are of many kinds and all degrees of “strength”; that is, a particular lot may contain few or many yeast cells and much or little of the acids, peptones, alcohols, &c., which have resulted from earlier fermentations. Probably the earliest barm made, as distinguished from leavens – was that from malt and hops as the baker in the first instance merely copied the brewer or the distiller.
This barm was known as compound or comp or patents. Some makers used a quantity of flour in the mixture, some did not. In Scotland, where barms were first made and where they continue in favour, the compound barm was displaced by a kind made with scalded flour and malt. To this was given the name of “Parisian”, although no precise evidence to show that it was copied from the practice of Parisian bakers. Another sort which may contain a little malt , but may be all scalded and raw flour, is called “Virgin barm”.
A kind much used in Australia, South Africa &c. has boiled potatoes, sugar, baked flour and bran as the consituents of the mash. This is called “spontaneous” or ”spon”, probably because, in the regions in which it is used, the liquid will start fermenting without a “stock” of old barm, and mature sufficiently to be used for bread making, by a straight dough process, under such conditions in about 30 hours.
Barms have of course, to be used in comparatively large quantity, It is a strong barm that contains12oz of yeast to the gallon, and the work is done by the yeast cells only. Barms have much influence on the nature of bread. Flour barms produce a condition of crumb that might be described as raw; it seems moist and clinging, but the bread is white and its skin smooth. As a rule, except in the case of “spontaneous” referred to above, barms are used with a long process of fermentation, either in two or three stages, and the flavours attributed to the barm may really be due to the changes in material within the dough, resulting from the processes.
From The Baker’s ABC by John Kirkland, formerly Head Teacher of National School of Baking, published 1927 by Gresham