Yeast, or Barm, is the froth or scum which rises on beer, during the act of fermentation.

Yeast is an article of the greatest importance in domestic economy ; forming a in head, which would otherwise become heavy and unwholesome. As it cannot at all times be obtained in sufficient quantities, we propose to state various methods which have been contrived, for generating and preserving this commodity.

In the. 2d vol. of the " Memoirs of the Philosophical and literary Society of Manchester, " Mr. Henry has published a method of preparing artificial yeast, by which good bread may be made, without the aid of any other ferment. He directs flour and water to be boiled to the consistence of treacle ; and, when the mixture is cold, to saturate it with fixed air. Next, it must be poured into large bottles with narrow mouths, which should be loosely covered with paper; and, over this, with a slate and a weight, to keep them steady. The bottles ought now to be placed in a room, the temperature of which is from 70 to 80° ; and the mixture be stirred two or three times in the course of 24 hours. At the end of about two days, according to Mr. H., such a degree of fermentation will have ensued, that the mixture acquires the consistence of yeast. In this state, the flour, intended to be made into bread, must be incorporated with such artificial barm, in the proportion of 6lbs, of the former to one quart of the latter, and a due quantity of warm water. The whole is now to be kneaded together proper vessel, covered with a cloth, and suffered to stand for 12 hours, or till it be sufficiently fermented ;. when it should be formed into loaves, and baked. Mr. Henry adds, that this yeast would be more perfect, if a decoction of malt were substituted for water.

A simple decoction of malt, however, is now fully proved to be convertible into yeast, fit for brewing : this discovery was made by Mr. Joseph Senyor, on whom the Society for the Encouragement of Arts, in the year 1790, conferred a bounty of 20l. He directs 3 wooden or earthen vessels to be procured, one being capable of holding 2 quarts, the other 3 or 4, and the third 5 or 6 quarts. A quarter of a peck of malt is then to be boiled for 8 or 10 minutes, in 3 pints of water; when one quart must be poured off the grains into the first vessel: as soon as the liquor becomes cool, such vessel ought to be removed towards the fire, or to a temperature of about 70 or 80° of Fahrenheit's thermometer. In the course of 30 hours, the fermentation will commence ; when 2 quarts of a similar cool decoction (made, we suppose, from the same malt), must be mixed with this yeast, in the second, or larger vessel; and be repeatedly stirred in the manner practised in common vats. As the fermentation increases, a greater portion of the like decoction must be added, and be worked in the largest vessel: thus, at length, a sufficient quantity of yeast will be produced, for brewing 40 gallons of beer.

This useful contrivance of Mr. Senyor, is farther confirmed by the recent experiments of a correspondent, whose plain and interesting account we are induced to quote in his own words : " I caused (says he) a gallon of rather weak wort to be made ; with part of which, when cool, I filled the middle part of Nooth's machine-: as soon as it was thoroughly saturated with fixed air, I mixed the whole, and placed it in a wooden vessel near the fire, the weather being rather cool. In about 24 hours, there were some faint signs of fermentation ; yet, at the expiration of the fourth day, I obtained no more than two table-spoonfuls of very indifferent yeast; and the wort had become extremely offensive. As the yeast was not only very poor, but in too small a quantity for any domestic purpose, I made an infusion of malt and a decoction of hops, in the manner used among the inhabitants of the island of Jersey, when they find it necessary to increase a small quantity of brewer's yeast. To this preparation, I added my two spoonfuls of yeast; let the mixture stand 24 hours ; then poured off the watery part; mixed the sediment with an increased proportion of the malt and hops; which fermented, and produced yeast enough to work a gallon of strong-beer, that yielded. a pint of very fine yeast, of which excellent bread was made. Having some reason to suspect, that the fixed air was of little or no use in this experiment, and that a wort might be made, which would ferment of itself, before the liquor were spoiled by too long keeping, I caused to be made four gallons of good wort, rather above porter strength, well hopped, and with a considerable quantity of colour, and treacle, to preserve it from putrefaction. It was equally divided, one-half impregnated with fixed air, as in the first experiment; each was put into a wooden vessel; and both were placed in an equally warm situation. At the expiration of 24 hours, there being no signs of fermentation, I stirred in a tea-spoonful of salt, and shook a little flour on the surface of each. In 12 hours more, the unimpregnated wort shewed some appearance of fermentation, which went off, and was renewed by placing the liquor near the fire ; and at the seventy-fourth hour, it had a tolerably good head of yeast ; but the impregnated wort was only beginning to ferment. In 24 hours after, we took a pint of yeast from the wort which was not impregnated with fixed air, and about a tea-cupful from the other, which was as inferior in quality as in quantity. The worts were then mixed, put into other vessels, and bid fair to become excellent beer. - I cannot say that this is a very expeditious mode of making yeast; but I believe it is a sure one, and within the power of every person who can procure the necessary ingredients for making good beer." - Our correspondent, therefore, conceives to have proved by this experiment, " that fixed air is, at least, not requisite to produce a fermentation in beer."

Dr. Lettsom ("Hints for pro-moling Beneficence, " etc. 1797) recommends the following preparation as a substitute for yeast : Boil 4 oz. of flour in 2 quarts of water, foe half an hour; and sweeten it with 3 oz. of Muscovado sugar. When the mixture is nearly cold, pour it on 4 spoonfuls of yeast, into an earthen or stone jar sufficiently deep to admit the new barm to rise : it must now be well shaken; placed near the fire for one day; and then the thin liquor be poured off the surface. The remainder is next to be agitated, strained, closed up for use, and kept in a cool place. Some of the yeast, thus prepared, ought always to be preserved, for renewing or making the next quantity that may be wanted.

The following method of preparing excellent yeast, we state from the " Transactions of the Econo' mical Society of Petersburg" on the authority of Baron Von Mest-macher : When the wort is made, and it becomes necessary to provide yeast for its fermentation, he directs 40 gallons to be drawn off, into a vessel provided with a lid, and capable of holding one-third more than that quantity. Next, 7lbs. of leaven are to be dissolved in a little wort, and mixed with the 40 gallons : 17 lbs. of rye-meal, and an equal quantity of ground malt, must now be added, by agitation for some minutes, and suffered to stand for half an hour. At the end of that time, a spoonful of the best yeast ought to be incorporated with this compound ; the lid be placed upon the vessel; and the whole remain undisturbed for 48 hours ; when the mixture will be found converted into 60 gallons of remarkably good barm.

In the 1st vol. of "Annals of Agriculture, " Mr. Kirby suggests mealy potatoes to be boiled, till they become perfectly soft; in which state, they must be mashed with hot water, so as to acquire the consistence of yeast. Two ounces of coarse sugar, or molasses, are then to be added to every pound of potatoes ; .and, when the mixture is luke-warm, two spoonfuls of barm must be stirred into it, according to the proportion above stated. This composition should now be removed towards the fire, or to a warm place, till the fermentation cease; when a certain portion may be kneaded with flour, which ought to stand eight hours before it is baked. - Mr. K. observes, that every pound of potatoes, thus managed, produces nearly a quart of yeast, which will remain good for three months. - The roots, however, ought, in the opinion of Mr. BoRdley, to be perfectly ripe and well-sprouted; as, in the contrary case, no fermentation will ensue.

Similar to this preparation, is the substitute for yeast contrived by Mr. Richard Tillyer Blunt; in consequence of which he obtained a patent, in October, 1787. - He directs 8 lbs. of potatoes to be boiled in water, in the same manner as for the table: after which they must be mashed ; and, while they are warm, 2 oz. of honey, or other saccharine matter, and one quart of common yeast should be added. - Three pints of this compound are sufficient, with the aid of warm water, for making the sponge; and, when this begins to sink, the dough ought to be formed into loaves, and baked.

An useful substitute for yeast, may be obtained by nearly rilling a bason, or tea-cup, with bruised or split pease, and pouring on them boiling water: the whole is now to be set on the hearth, or other warm place, for 24 or 48 hours, according to the temperature of the season : at the end of that time, a froth, possessing all the properties of yeast, will appear on the surface of the fluid. This method, we understand, is commonly practised in the eastern countries ; and the barm, thus procured, is said to render the bread light and palatable.

To the different modes of procuring yeast, already specified, We shall add an easy and expeditious process, which appears to be very plausible; and has lately been communicated to the Editor, by an anonymous correspondent ; though he cannot vouch for its success. - Take six quarts of soft water, and two handfuls of wheaten or barley-meal ; stir the latter in, before the mixture is placed over the fire, where it must very gradually simmer, and at length boil, till two-thirds of the fluid be evaporated, so that it may consist of two quarts. When this decoction becomes cool, incorporate with it (by means of a whisk) a powder, consisting of two drams of salt of tartar, and one dram of cream of tartar, previously mixed. The whole should now be kept in a warm place. - Thus, a very strong yeast for brewing, distilling, and baking, is said to be obtained. For the last mentioned purpose, however, such barm ought to be first diluted with pure water, and passed through a sieve, before it be kneaded with the dough; in order to deprive it of its alkaline taste.

The preservation of yeast, for a considerable time, is an object of equal importance to that of producing it artificially : hence, it has been recommended to put a quantity of that commodity into a canvas bag, and to submit the whole to the action of a screw-press, so as to deprive it of all moisture; in consequence of which, the barm will remain in the bag, as firm and tough as clay : in this state, it must be packed in casks, well secured from the access of air, and may be kept in a sound state for any period of time. We believe, however, it would be more safe and advisable to form the pasty yeast into circular, flat resembling ten-saucers., and in that state to dry the whole mass, either in the open air under shade, or in the moderate warmth of a baker's D.

Mr. Felton Mathew's mode of separating beer from yeast, and preserving the latter (for which he obtained a patent, in February, I796), in many respects corresponds with that just described: the principal difference is, that he directs the bags to be placed in troughs perforated with holes, to prevent the former from bursting ; and then to submit them to the action of a lever, aided by incumbent weights. When the beer is thus expressed, the yeast remaining in the bags, will crumble into coarse powder: this must be spread on canvas, hair-cloth, or similar porous material, and gradually dried in a malt-kiln, or in any room or stove, where a regular temperature of from 80 to 90 degrees is maintained ; and, lastly, as soon as it becomes perfectly dry, the barm must be packed in bottles or casks, from which the air is completely excluded.

Another mode of preserving yeast, consists in throwing a withy, or the young shoots of willows twisted together, into the vessel where the yeast is working 5 and suspending them in a warm room, till the next opportunity of brewing arrives. We conceive, how-, the following expedient to be preferable, both in point of cleanliness and economy ; it being suc-lully practised by some careful house-wives: - Take a clean wooden bowl, of such size as may be most convenient; spread a regular coating of yeast around its inner surface ; and, as often as this dries, repeat the process, till a thick cake be formed: the vessel must be kept in a dry place. When any barm is wanted, a small piece may be cut out; and, after dissolving it in warm water, the solution will answer all the purposes of fresh yeast, whether designed for baking, or for brewing.

The. following process being advantageously employed in Germany, for preserving barm, so as to be fit for all domestic uses, after a considerable time, we have inserted it for the benefit of our country-readers : When the yeast is taken from new beer, it must be put into a clean linen bag, and be laid in a vessel half full of dry, sifted wood-ashes : the whole is then to be covered to the thickness of three or four inches with similar ashes, and be pressed together. In this situation, the barm should remain for a day, or longer, if it be necessary ; when the ashes will absorb all the moisture, and the yeast acquire the consistence of a thick paste. It must now be formed into small lumps, or balls ; dried in a moderate heat; and kept in bags, in an airy, dry place : when any barm is wanted, a few of such balls may be dissolved in warm water; or, which is preferable, in beer; and they will answer every purpose of fermentation.

Beside its utility in baking and brewing, late experiments have fully proved, that yeast is of singular efficacy in putrid fevers, putrid sore throats, and similar malignant complaints: for the first discovery of this important fact, we are indebted to the Rev. Edmund Cartwright. The dose of barm, according to his experience, and that of other practitioners, is two large'spoonfuls, to be repeated every three hours : in some cases, this has been sufficient; but, in others, it was necessary to administer the Peruvian bark, between each dose. In a few instances, indeed, emetics and laxatives were given previously to taking the yeast; but, in general, this simple remedy seldom failed to effect a cure; provided due attention was bestowed on the diet and regimen of the patient.