15. Fermentum cervisiae.—Barm or Yeast.

(Cerevisiae Fermentum, L.D.)

History.—Leaven and ferment have been known from the most remote periods. Leaven (or sour dough), called in Hebrew seor [Hence the German sauer and English sour.], and ferment, termed in Hebrew khametz [The sour fermented mare's milk used by the Tartars appears to have derived its name, koumiss, from the Hebrew khametz.], are both referred to in the Old Testament: the one applies to solids, the other to both solids and liquids. In the common version, however, both these Hebrew words are translated leaven [In Exodus, xiii. 7, the terms seor and khametz occur together, and are evidently distinct. "Unleavened things (matzah) [άζυμα] shall be consumed during the seven days, and there shall not be seen with thee fermented things [ξυμωτόν], and there shall not be seen with thee leavened mass [ξύμη]."—Biblical Cyclopaedia, vol. ii. pp. 236-7.) The interpolated Greek words are from the Septuagint.]. The Greeks appear to have used the term ξύμη in a general sense, to include both leaven and ferment. Dioscorides [Lib. ii. cap. 107.] speaks of the medical properties of the leaven of wheat (άλενρων ξύμη), which Galen [De Simpl. Med. Facult. lib. vi. cap. vi. § 3.] and Paulus [Paulus Aegineta, trans. by F. Adams. Syd. Soc. Ed. vol. iii. p. 126.] simply call ξύμη. Pliny [Hist. Nat. lib. xviii. cap. 12 and 26; lib. xxii. cap. i2. Ed Valp.] distinguishes leaven (fermentum) from beer yeast (spuma cervisiae).

The history of the discovery of the vegetable nature of yeast is an interesting subject of inquiry. So long since as the year 1680, Leeuwenhoek [Arcana Naturae delecta, p. 1, et seq. ed. nov. Lugd. Bat. 1722.] described and figured the globules of beer-yeast. He was fully aware of its vegetable nature, but was ignorant of its power of vegetating or growing, and notwithstanding the high magnifying power which he used, he failed to detect the presence of the granules or nuclei in the interior of the yeast-cells.

In 1826, Desmazières [Desmazière's observations were first published at Lisle. They were afterwards reprinted in the Annals des Sciences Naturelles, t.x.p. 42, 1827.] published some observations on Persoon's genus Mycoderma, which he defined anew, and referred to Gaillon's class of infusory animals, called Nemazoaria (now placed among Algae). He described a Mycoderma vini, glutinis farinulae, malti-juniperini, malti-cervisiae, and cervisiae. The latter is frequently considered to be the yeast-plant; but Desmazières confounded two things which deserve to be considered entirely distinct, namely, the yeast-plant, properly so called (the Torula Cerevisiae of Turpin), and a larger filamentous confervoid plant, to which more strictly the name of Mycoderma Cervisiae of Desmazières should be confined.

To Cagniard-Latour is due the credit of establishing the real nature of yeast. During the years 1835 and 1836, he communicated to the Société Philomathique some researches on ferments, which were published in the journal called l'Institut (Nos. 158, 159, 164, 165, 166, 167, 185, and 199); and on the 12th of June, 1837, he presented to the Academy of Sciences his Mémoire sur le Fermentation Vineuse, a notice of which appeared in the Comptes Rendus of that period. The report [A translation of this report appeared in Jameson's Edinburgh New Philosophical Journal, vol. xxv.] on this memoir, drawn up by Turpin, in the name of himself, Thenard, and Becquerel, was made to the Academy in July, 1838 (Comptes Rendus); and the memoir itself was printed in the 68th volume of the Annales de Chimie et de Physique, 1838.

About the same time, Schwann [Poggendorff's Annalen der Physik, Bd. xli. p. 184, 1837.] was occupied in investigations on this subject, but his observations were not published until 1837. He denied that the organized being found in fermenting liquids is one of the infusoria, as Desmazières had supposed, but asserted that it is undoubtedly a plant, and that it has great resemblance to many jointed fungi. Meyen, who examined it at Schwann's request, agreed as to its vegetable nature, and considered that the only doubt which could exist respecting it was, whether it was an algal or a fungus, but its deficiency in green pigment led him to regard it as a fungus. The filamentous fungus found in saccharine solutions which are undergoing fermentation, Schwann, therefore, proposed to to call the sugar-fungus (Zuckerpilz). Meyen [Report on the Progress of Vegetable Physiology during the year 1837, translated by W. Francis, pp. 83-84, London, 1839.] adopts Schwann's proposal, and refers to three species of Saccharomyces, viz., S. vini, S. cerevisiae, and S. pomorum.

In 1837, Kützing [Journal für praktische Chemie, Bd. xi.] described and figured the yeast-plant.

On the 20th of August, 1838, Turpin [Mémoire de l'Académie Royale des Sciences, t. xvii. 1840.] read to the Academy of Sciences at Paris, his valuable Mémoire sur la Cause et Its Effets de la Fermentation Alcooliquc et Aceteuse.

The notion that yeast was an organized being, in fact a living plant, was at first strongly opposed by Berzelius and Liebig [In Liebig's Annalen der Pharmacie, vol. xxix. p. 100, 1839, a satirical paper (The Mystery of Vinous Fermentation unfolded) was published, representing yeast to be an infusory animal which fed on sugar, and evacuated by the alimentary canal spirit of wine, by the urinary organs carbonic acid. In his Chemistry in its Application to Agriculture and Physiology, edited by Dr. Playfair, 2d edition, 1842, Liebig declares yeast to be a body in a state of decomposition, and states that the idea of its reproducing itself, as seeds reproduce seeds, cannot for a moment be entertained. But in the third edition of his Animal Chemistry (edited by Dr. Gregory, 1846), he does not attempt to deny the vegetable nature of yeast, though he thinks that investigation into the nature of this substance is not yet completed.]; but was soon adopted by the eminent chemist Mitscherlich [See the Report of the Academy of Sciences at Berlin for February 1843, quoted in the translation of Link's Report on the Progress of the Physiological Botany, published by the Ray Society, p. 428, 1846.].

Botany.—The substance called yeast is a mass of microscopic cryptogams.

The organization and vitality of yeast are demonstrated by the form and structure of its particles, as determined by the microscope; by their chemical composition; by their reproductive power, as proved by the generation of yeast during the fermentation of beer; and lastly, by the effects of mechanical injuries [A very curious fact was mentioned to me by the importer of German and Dutch yeast, in Finch-lane, Cornhill, London: it is, that mechanical injury kills or destroys yeast. Foreign yeast is imported in bags, and of these great care is required in their removal from place to place. If they be allowed to fall violently on the ground, the yeast is spoiled. A bruise, as a blow given to the bag, also destroys it. The men who make up the dried yeast into quarter-pound and half-pound balls for sale, are obliged tohandle it very dexterously, or they injure and destroy it. In fact, falls, bruises, or rough handling, kill it, and the yeast which has thus been mechanically injured may be readily distinguished from good, unaltered yeast. Its colour becomes darker, somewhat like the change which an apple or pear ungergoes when it becomes rotten; and, from being crumbly and powdery, it becomes soft, glutinous, sticky to the fingers like flour-paste, and soon stinks. I have submitted some of this injured or dead yeast to microscopical examination, but have been unable to detect any difference in its appearance from healthy yeast. The effect of mechanical injuries is also noticed by several writers. Thus Liebig (Chemistry in its application to Agriculture, by Dr. Playfair, p. 286, 3d. ed. 1842) remarks that simple pressure diminishes the power of yeast to excite vinous fermentation.], of heat and cold [Boiling for a short period injures, and for a long period destroys, the power of yeast to excite fermentation (Berzelius). Cold interrupts fermentation, apparently by renderingthe yeast-plant torpid.], and of chemical and other poisons [The power of yeast to excite vinous fermentation is arrested or destroyed by alcohol, acids, alkalies, various salts (chloride of sodium, bichloride of mercury, nitrate of silver, &c.), volatile oils, excess of sugar, &c. (See Berzelius and Liebig; also, Quevenne, in the Journ. de Pharmacie, t. xxiv. p. 3334, 1838.].

Kützing [The following are, according to Kützing, the generic and specific characters of the Yeast-plant, which he calls Cryptococcus Fermentum, and refers to Mycophaceae (Pilztanze), a sub-order of Algae.

Cryptococcus.—Mucus hyaline globules, collected in an intermediate mucous stratum.

C. Fermentum.—Submersed: globules elliptical, solid, in the centre 1- or 2-punctate.], who is a believer in the convertibility of some of the lower algals into species, or even genera, of a higher organization, is of opinion that yeast is an algal in its lowest, but a fungus in its highest, grade of development.

It is more probable, however, that this plant is a fungus in all stages of its existence; and that what we know as yeast is either a mass of sporidia or the separated joints of the spawn or mycelium of a fungus whose more perfect state is at present undetermined, but which is probably a mucedinous fungus, perhaps allied to Penicillium. In the present state of uncertainty, I have thought it preferable to designate it by its more classical name (Fermentum Cervisiae) than to adopt any of the following botanical names, which have been given to it: Mycoderma Cervisiae, Desmazières; Torula Cerevisiae, Turpin; Cryptococcus Fermentum, Kützing; Saccharomyces Vini et Cerevisiae, Schwann and Meyen. For while Mycoderma is a spurious genus (Fries and the Rev. M. J. Berkeley), the yeast-plant has been declared, by an eminent fungologist, to be certainly no Torula; and as Kützing's notion of its algaceous nature is not admitted by botanists, his name of Cryptococcus Fermentum is scarcely admissible for it.

When submitted to microscopic examination, yeast is found to consist of globose, or more or less ovoidal, ellipsoidal, or somewhat pyriform, transparent, nucleated cells, varying in size from 1/7500th to about 1/2500th of an English inch. The nucleus appears to me to consist of a mass of granules or nucleoli of unequal size: some of the larger ones are highly refractive, and probably contain oily or fatty matter. The nucleoli are called by Turpin, globuline.

Turpin spent a night in a brewery to examine the changes which the yeast undergoes during the fermentation of beer. The fresh yeast had the appearance indicated in Fig. 176. In one hour after it had been added to the wort, he says that germination had commenced; the maternal cells had produced one or two buds or young cells (see Fig. 177). In three hours many of the cells were didymous, or double, the buds having attained the size of the maternal cells, and some of them had themselves begun to produce other buds or young cells (see Fig. 178). In eight hours the cells were arranged in rows, forming moniliform mucedinous plants, composed of several cells or joints, which varied somewhat in diameter and shape. Terminal, and in some cases lateral, buds or young cells were observed, showing that the plants were about to ramify. Some of the smaller rows were seen to explode and emit a fine powder, consisting of minuter globules (see Fig. 179). Turpin placed some yeast-cells in an aqueous solution of sugar, and in three days observed that jointed filaments, with lateral branches, were produced (see Fig. 180).

I have myself examined yeast at Messrs. Hanbury and Buxton's brewery at various stages of the fermentation of both porter and ale, from a few hours to many days. In the more advanced stages of fermentation, I observed the globules of yeast were frequently in strings, or rows, apparently forming moniliform often branched plants. But as the cells or joints were very readily separable, I could not satisfy myself that the adhesion was otherwise than mechanical, such as we see between the blood-disks when they arrange themselves in series like money-rolls, and such as we sometimes perceive even in inorganic amorphous precipitates. My experience agrees precisely with that of Schlossberger [Pharmaceutical Journal, vol. v. p. 131, 1845.], who states that he "never could perceive a budding or bursting of the yeast-cells, accompanied by a discharge of their contents, nor could I ever produce this by compression. These curious brachial and other adjustments of the cells of yeast to each other, appeared to me the work of chance." It is, however, proper to add, that the artificial rupture of the cells has been effected by Mitscherlich, who also confirms Turpin's observation of the budding of the yeast-cells (see p. 84).

Origin.—It is well known that a pure solution of sugar will not undergo fermentation when exposed to the air, but a saccharine vegetable juice, which contains albuminous matter (as the juice of the grape), suffers spontaneous fermentation, and this process always begins with the formation of yeast-cells.

By some it is assumed that these arise from yeast-germs floating in the air, and which, meeting with a fit receptacle for their development in the vegetable juice, germinate and grow, and effect vinous fermentation. By others their production is ascribed to a generatio primitiva.

Turpin was of opinion that there are three sources or modes of production of the yeast-plant: 1st, the transformation of globuline into yeast-cells; 2dly, budding, or the separation of the joints of moniliform stems; 3dly, the escape of spores (globulins seminulifères) from the interior of the cells: Mitscherlich admits the two latter modes of growth.

The amylaceous particles contained in the cells of the albumen of barley (see Figs. 181, 182) are called by Turpin globuline. The transformation of these into yeast-cells is, according to the same authority, the primitive origin of beer yeast. Dr. Lindley [Introduction to Botany, p. 113, 4th ed. 1848] partly confirms Turpin, for he states that he has seen these smaller granules sprout during fermentation; and he adds, that they have at that time lost all their starch, for iodine produces no sensible effect upon their colour.

Turpin states that 35 lbs. of dried or pressed yeast produced during the brewing 5700 litres [about 14 butts] of beer 247 lbs. of dried or pressed yeast: that is, an actual increase of 212 lbs. of new yeast.

In the deposit from the porter refrigerator of Messrs. Truman and Hanbury's brewery, I have observed the forms deposited in Fig. 183, c, d, e, and f. These constitute the plant called by Desmazieres the Mycoderma Cervisiae.

Occurrence in the Human Body.—Yeast-cells have been found in the human body. Hannever detected them in the black coating of the tongue of a typhoid patient. They have also been discovered in the liquids of the oesophagus, stomach, and intestine. In some cases, probably, they may have been introduced by the beer drank by the patient; but, in other cases, their presence could not be accounted for in this way. As they are developed in the urine of diabetic patients, their occurrence in urine has been supposed to indicate the existence of sugar, but they have been found also in non-saccharine urine. [Des Végétaux qui croissent aux l'Homme et sur les Animaux, par M. Ch. Robin, Paris, 1847.]

Description. In commerce, three varieties of yeast are known and distinguished. These are, brewers' yeast, dried yeast, and patent yeast.

1. Brewers' yeast.—In breweries, two kinds of may be distinguished, namely, upper or top yeast, and lower or bottom yeast. These have been described by Mitscherlich [Poggend. Ann. lix.; also, Chem. Gazette, vol. i. p. 568, 1843.].

Top yeast consists of large cells, at the extremities of which small ones are developed. It appears, therefore, to be produced by buds. Berlin, the most beautiful top yeast is obtained at a temperature of 77° F.

Bottom yeast consists of cells of various sizes, without any small globules attached to the large ones. It appears to be produced by the growth of small isolated granules (spores?), which Mitscherlich thinks have escaped from the yeast-cells which have burst and disburthened themselves of their contents. Bottom yeast is multiplied at a lower temperature than top yeast: Mitscherlich says, that the bottom ferment of Bavarian beer is produced at a temperature which must not exceed 48° F. nor go below 32° F. The bottom yeast sold at breweries is generally impure.

Brewers and bakers distinguish yeast according to the quality of the beer from which it is obtained. Ale yeast is the best and strongest; and used for bread-making. Porter yeast is objected to by bakers, but is used in distilleries. Small-beer yeast is said to be weak, but rapid in its effects, and is sometimes used in making rolls.

2. Dried yeast.—Under this name is sold a granular or pasty mass of yeast-cells, which have been separated from mechanically admixed solids, as well as from the supernatant fermented liquid, probably by filtration through linen cloths and subsidence. That which is sold in London is imported from Holland, Belgium, and Germany, and is commonly called German yeast. It comes over in hempen bags, each holding half a hundred weight. If transported in casks it is apt to burst them, unless they are strongly iron-bound, by the quantity of carbonic acid which it evolves.

3. Patent yeast.—This might with more propriety be called artificial yeast. It is a watery liquid, containing yeast-cells, and which has usually been prepared purposely by the fermentation of an infusion of malt and hops. The hops probably contribute to prevent the liquid becoming rapidly sour. Turpin thinks that their oil may act as a stimulant in the development of the yeast-plant. I am informed by a baker that he prepares patent yeast for bread-making by mashing half a peck of ground malt with six gallons of water at 170° F.; then boiling the wort with half a pound of hops; and to the cooled liquid adding some brewers' yeast. In 24 hours the patent yeast is fit for use [Various receipts for making yeast are given in Webster's Encyclopaedia of Domestic Economy, p. 760.]. It rapidly turns sour in warm weather; and I am informed that bread made with it does not keep so well as that prepared with other kinds of yeast. It is in general use among bakers, especially those who use an inferior kind of flour.

Mr. Fownes [Pharmaceutical Journal, vol. ii. p. 403, 1842.] describes the following mode by which he prepared some artificial yeast: "A small handful of ordinary wheat-flour was made into a thick paste with cold water, covered with paper, and left for seven days on the mantle-shelf of a room where a fire was kept all day, being occasionally stirred. At the end of that period three quarts of malt were washed with about two gallons of water, the infusion boiled with some hops, and when sufficiently cooled, the ferment added. The results of the experiment were a quantity of beer (not very strong, it is true, but quite free from any unpleasant taste), and at least a pint of thick barm, which proved perfectly good for making bread."

Composition.—Yeast has been analyzed by Marcet [Quoted by L. Gmelin, Handb. d. Chem. Bd. ii. S. 1100.], by Dumas [Traité de Chimie appliquée aux Arts, t. vi. p. 316, 1843.], by Mitscherlich [Lehrbuch d. Chemie, 4. Aufl. S. 370 (quoted by Schlossberger).], by Mulder [The Chemistry of Vegetable and Animal Physiology, translated by Dr. Fromberg, p. 49; also, Pharm. Central Blatt für 1844, S. 891.], and by Schlossberger [Ann. d. Chem. u. Pharm. Bd. li. S. 193, 1844; also, Pharm. Journal, vol. v. p. 42, 1846.].

It consists of two parts, the cell-walls, composed of a kind of cellulose, and the contents of the cells, composed of a proteine substance, and probably fat, or oil.

1. Cell-walls.—By digesting yeast in a weak solution of potash, the contents of the cells are removed, and the membranous matter composing the cell-walls is left. In its composition it approximates to cellulose or starch.

2. Content of the Cells.—According to both Mulder and Schlossberger, yeast-cells contain a substance allied to the proteine bodies.

Besides traces of phosphorus and sulphur.

Mulder regards the contents of the cells as being the hydrated oxide of proteine, C₄₀H₃₇N₅O₂₆=C₄₀H₃₁N₅O₁₂+O₈+6HO.

It is probable that, besides a proteine body, the cells contain a fatty, or oily substance. Schlossberger states that he extracted a yellow oil from yeast by means of ether.

3. Ashes.—According to Schlossberger, the ashes of upper yeast amounted to 2.5; of lower yeast, to 3.5 per cent.

Physiological Effects.—The effects of yeast on the animal economy are, if at all, not very obvious. The constituent of the cell-walls is insoluble, and therefore inert. The contents of the cells may, perhaps, be slightly nutritive. To the evolved carbonic acid have been ascribed the topical antiseptic effects of yeast.

The tonic and laxative effects ascribed to beer yeast, are probably referable to the fermented malt liquor in which the yeast-cells are usually contained and exhibited (see Wort).

Uses.—Yeast is employed both for medicinal and chemical purposes.

As a medicine, yeast has been used both internally and externally. Internally, it has been administered as a tonic and antiseptic in typhoid fevers. Dr. Stoker [On Continued Fever, p. 121, Dubl. 1829-30.] states, that it usually acts as a mild laxative, improves the condition of the alvine evacuations, and is more effectual in removing petechiae and black tongue than any other remedy. It is admissible where cinchona and wine cannot be employed, on account of the inflammatory symptoms. The dose of it is two tablespoonfuls every third hour, with an equal quantity of camphor mixture. Enemata of yeast and assafoetida are said, by the same writer, to be efficacious against typhoid tympany.

Externally, it has been used in the form of poultice. (See Cataplasma Fermenti.)

Yeast is an important agent in panification and brewing. In some cases of dyspepsia, unfermented bread appears to agree better with the stomach than fermented bread, which is supposed to derive an injurious quality from the yeast used in its preparation.

Yeast is sometimes added to liquids to excite the vinous fermentation, and thereby to detect the presence of saccharine matter.

L. Gmelin [Recherches Expérimentales sur la Digestion, Paris, 1826.] employed this test to detect sugar in the animal fluids after the ingestion of amylaceous food. Dr. Christison [The Library of Practical Medicine, vol. iv. art. Diabetes, p. 249.] found it so delicate, that he could detect with it one part of sugar in 1000 parts of healthy urine of the sp. gr. 1.030. Messrs. Richard Phillips, Graham, and George Phillips [Parliamentary Report.], used it to detect the presence of saccharine matter in tobacco adulterated with this substance. (For the mode of using this test, see Saccharum.)

1. CATAPLASMA FERMENTI, L.; Cataplasma Fermenti Cerevisiae; Yeast Poultice.—(Yeast, Water heated to 100° F., of each f℥v; Flour lb j. Mix the yeast with the water, and add the flour, stirring so that a poultice may be made. Place it before the fire until it swells up.)—It is applied, when cold, to fetid and sloughing sores as an antiseptic and stimulant: it destroys the fetor, often checks the sloughing, and assists the separation of the dead part. It should be renewed twice or thrice a day. I have frequently heard patients complain of the great pain it causes. The carbonic acid is supposed to be the active ingredient.

The following poultices are analogous in their nature and effects:—

2. CATAPLASMA FAECULAE CEREVISIAE, Guy's Hospital Ph.; Poultice of the grounds of beer.— (Grounds of beer; Oatmeal; as much of each as may be required to make a poultice.)—It is applied cold twice or thrice a day, in the same cases as the preceding preparation, to which its effects are analogous.

This poultice was formerly called [Chirurgical Pharmacy, p. 279, Lond. 1761.] the discutient cataplasm or cataplasma discutiens, and was applied to disperse tumours.

3. CATAPLASMA BYNES, Guy's Hospital Ph.; Malt-meal and Yeast Poultice; Malt Poultice.—(Malt-meal and Beer yeast; as much of each as may be required make a poultice.)—This poultice is to be applied warm.

The Elements of Materia Medica and Therapeutics, Vol. II, 3th American ed., was written by Jonathan Pereira in 1854.