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falling to the bottom, and others rising to the top of the fluid. The yeast before mentioned is thus separated among other matters, while the bulk of the fluid is materially increased. It is in this stage that we have the power of regulating the extent of the fermentation, by separating the floating leaven, or allowing it to return into the liquor. Hence, the process of fermentation in a full cask, ejecting that substance by the bunghole.

The disengaged gas is carbonic acid chiefly; but holding some alcohol in solution. It appears, by analysis, that this is the produce of part of the carbon of the sugar and of its oxygen; and this is the great change which leads to the production of the alcohol. But it also contains some obscure vegetable matter in suspension; because, if passed through water, it not only converts it into vinegar, but deposits that mucilage, which, in vinegar, is called the mother. It is possible, however, that this may itself be a new compound: and it is one which, in certain cases, contains azote.

All those juices of fruits which undergo the vinous fermentation, either with or without the addition of sugar, contain an acid. Vegetable acids are obtained chiefly from fruits. The apple, for instance, contains malic acid; the lemon, citric acid; the grape, tartaric and malic acids. The marquis de Bouillon has ascertained that must will not ferment if all the tartar which it contains be separated from it; but it ferments perfectly well on restoring that salt. The same chemist ascertained that the strength of wine is considerably increased by adding tartar and sugar to the must. We may conclude from these facts that the presence of a vegetable acid is of importance in these spontaneous fermentations. It deserves attention, that Bouillon obtained more tartar from verjuice than from wine; and he observed, that the more the proportion of sugar in grapes increased, the more that of tartar diminished.

It seems more than probable, from the experiments of Bouillon and Chaptal, that the tartaric acid is partly decomposed during the fermentation, and that a portion of malic acid is formed. The process, therefore, is more complicated than was suspected by Lavoisier. It is obviously analogous to combustion, as is evident from the evolution of caloric and the formation of carbonic acid, which is a product of combustion. Proust has ascertained that, during the fermentation, not only carbonic acid, but azotic gas also, is disengaged. This is a demonstration, that all the constituents of must are concerned; for sugar does not contain that principle. Thenard could detect no azote in the carbonic acid from

wort.

We have already seen that a vinous fermentation, to be perfect, requires very exact proportions of mucilage and saccharine matter, so as to have the one just sufficient to destroy or attenuate the other; in which case the result will be, if the operation has been properly conducted, a mixture of alcohol and water, differently flavored, according to the materials from which it is produced, as grapes, pears, apples, or malt and hops; but such accuracy in the

proportions cannot be expected, either from nature working at large, and varying in every climate, soil, and situation, or from our most ingeniously conducted experiments.

A perfect fermentation, therefore, has been considered an object almost impossible to be obtained; and all we wish to show is, that the errors of the mixture may be corrected, and the whole process improved, by good management.

The common practice, until a few years back, has been to ferment in open vessels; and though it was a circumstance well known among chemists, that a certain portion of spirit and flavor escaped in the form of vapor during the process, yet no one had an idea that the condensatory system could be applied, as it appeared impossible to effect the fermentation in air-tight vessels, being unable to surmount the great difficulty which existed of keeping down and managing that enormous bulk of non-condensable gases, which are emitted during the decomposition of the saccharine matter, and which acquire greater expansive force by the gradual increase of heat.

The idea, however, occurred to Madame Gervais, that distillation might be carried on during the fermenting process. Having come to this conclusion, she proceeded to construct an apparatus that would operate in such manner as to return into the vessel the spirit and the flavor that was evolved from the fermenting gyle, and let out the non-condensable gases, which might, by the increasing heat, acquire too great an expansive force, and burst the working-tun. A short description of this apparatus will be a fresh proof that the greatest advantages are often derived from the most simple means.

It consists of a vessel resembling the head of the ancient still, and constructed of such form as to be capable of being placed securely on the back, or vat, in which the process of fermentation is to be carried on; the back or vat must be closed air-tight, with a hole in the top, communicating with that part of the apparatus called the cone, or condenser This cone is surrounded by a cylinder or reservoir, which is to oe filled with cold water, so that the alcoholic vapor, or steam, evolved during the process, may be condensed as it comes in contact with the cold interior surface of the cone; and, being thereby converted into a liquid, trickles down the inside of the condenser, and through a long pipe is returned into the fermenting liquor.

By the application of this apparatus, a considerable portion of alcohol, which has been hitherto suffered to escape in the form of vapor, along with the non-condensable gases, is condensed and returned into the liquor; and the non-condensable gases are carried off by a pipe, which, proceeding from the interior lower part of the cone, and running up the inside of the cylinder in the cold water, passes out through the side, and the end is immersed some depth below the surface of water contained in a separate vessel, permitting the gases to escape, but still under a certain degree of pressure, the object of which is to confine the alcoholic steam and gas within the cone, and allow them a sufficient time

to cool and condense.

To obtain a good fermentation, as complete a decomposition of the must or wort, and as perfect a recomposition of alcohol as possible, are the great objects to be obtained. To acquire the former, three requisites are necessary-fluidity, heat, and motion; the latter-density, coolness, and tranquillity.

Let us examine each of these separately; first, of fluidity.

The specific gravity of the liquid most eligible to produce a good fermentation, is between 1020 and 1-140, or eighteen, and 132 pounds by Dicas's improved saccharometer, made by Joseph Long. Below eighteen pounds of real extract per barrel, the liquid is too thin to produce a proper fermentation, and above 132 pounds it is too thick; but, supposing the specific gravity of the must or wort to be correct, it may be carried beyond a proper dilatation by too much heat, or congealed to too great a consistency by excessive cold; consequently either a thunder-storm or hard frost will derange the operation, and are equally injurious to fermentation. Any method, therefore, that will ensure an even temperature must be of great importance; and such a method is obtained by applying the apparatus already described, since, by preventing the access of atmospheric air, the sudden changes of the external temperature can have no effect upon the fermenting gyle; and if it has been commenced at a proper heat (which is between sixty-five and eighty), will proceed through its different stages, as well during the hottest days of summer, as in the selected months of autumn and spring.

With respect to motion, we are indebted to M. Gay Lussac, as we have already stated, for a beautiful and important experiment, proving that must, possessed of all the requisites to produce a good fermentation, will not begin to ferment unless excited by a foreign agent. He placed the must in a close vessel, from which the atmospheric air had been exhausted, where it remained several days without giving any signs of fermentation, from which he concluded some power was wanting to break the union of its constituent principles; he therefore introduced a small quantity of oxygen, which immediately caused the must to ferment, evidently proving the necessity of a small portion of atmospheric air (which contains oxygen), to allow the fermentation to commence. But it at the same time proves, that, after performing that office, this great enemy to all fermented liquors may be dispensed with, without impeding the process; as the small quantity of oxygen, introduced by M. Gay Lussac, was soon absorbed by the carbon to form carbonic acid gas, and he found no occasion for any further supply.

This discovery is of the greatest importance, since it enables us, without the least detriment or inconvenience to the process, to exclude the oxygen of atmospheric air, which, by constantly supplying the gyle with the principle that causes and promotes acidity, casts on it from the first that roughness and disagreeable flavor which spoil most of our common beverages.

Here again the new apparatus proves of great benefit, for, as soon as carbonic acid gas is evolved

VOL. IX.

from the fermenting gyle, the atmospheric air, being lighter, is driven out from the upper part of the working tun; and, as no air is permitted to enter afterwards, all the subsequent carbonic acid gas emitted, diminishes the quantity of oxygen contained in the gyle, by the oxygen uniting with the carbon as fast as it disunites from the saccharine matter during its decomposition, and thereby secures a soundness and peculiar mildness, not to be procured by any other mode.

The necessary conditions for a complete decomposition of the saccharine matter having been stated, it remains to notice those required for a good production of alcohol.

The first already mentioned is a certain density, in order to allow the several principles which are disunited to recombine. It is doubtful whether such a combination will in any case take place, until the temperature of the gyle, having attained its greatest heat, is afterwards cooled a few degrees; a fact confirming which is, that a portion of the liquid taken out when at its greatest heat, and tried by distillation, produced little or no spirit; but such refrigeration must not be effected too suddenly, as it might coagulate the yet undecomposed mucilage, and check its further action on the remaining saccharine matter; and by arresting that natural operation which ought to be pursued a longer or shorter period, according to the specific gravity of the fermentable matter, might produce that result termed 'ropiness,' by holding in solution the coagulated mucilage.

Here again the apparatus will be found of great service, for, by frequently renewing the cold water in its reservoir, the internal temperature will gradually diminish by the heat of the gyle coming in contact with the cold interior of the cone: but, in order to effect this, the tranquillity above mentioned is necessary, since the continual motion is caused by the oxygen soliciting new combinations with the carbon, and thereby constantly giving rise to a fresh supply of heat.

Besides the advantages already mentioned, which are common to all fermented liquors, there are others peculiar to each, that require to be explained.

The apparatus being applied to ferment the must of grapes, has been found to procure an increase of quantity, amounting in some instances to ten or twelve per cent., and which necessarily varies according to situation, season, or former management; but in no instance has it been found less than from five to six per cent.

When applied to the fermentation of beer, this saving has constantly been between four and a half and five per cent., a quantity certainly inferior to that obtained from wine, but which will not appear unimportant when it is considered that this saving is a spirit congenial to the nature of the beer, and an essential oil necessary to its preservation; in addition to the peculiar mildness and superior flavor.

Mr. Henry found, by a series of very interesting experiments, that malt infusion might be made to enter into complete fermentation by impregnating it with carbonic acid, prepared

M

from chalk and sulphuric acid, and the liquor thus fermented gave a yeast which made perfect bread, gave alcohol by distillation, and vinegar by further keeping. The wort itself undoubtedly contained all the ingredients of yeast, since this substance was produced during the fermentation; but the experiment is decisive to prove that no addition of azotic extract is required to begin fermentation in materials naturally fermentable, though, when once begun, the yeast, as fast as it was produced, must have assisted in the fermentation then going on. The evidence for the necessity of an acid to begin fermentation is, therefore, more decisive, but it is still doubtful whether any particular one is required, or whether there are not several which will answer the purpose. In Mr. Henry's experiments the acid employed was the carbonic, and, from the arrangement of the apparatus, probably a small portion of sulphuric was also carried in along with it. But in grape juice there is no proof of the existence of carbonic acid ready formed, though the tartaric, malic, and other vegetable acids contain within themselves the ingredients of carbonic acid, and are chiefly and ultimately resolvable into this acid. Yeast will ever. induce fermentation after it is pressed and dried into solid cakes (a practice not uncommon, as it will keep for a great length of time in this form), but after this operation it can hardly contain any carbonic acid ready formed, though with abundant tendency to reproduce it by the first mutual action of its constituent parts.

The attenuation of liquors, or the diminution of their specific gravity by fermentation, is very striking. This is shown by the hydrometer, which swims much deeper in fermented liquor, than in the same materials before fermentation. Much of this attenuation is, doubtless, owing to the destruction of the sugar, (which, dissolved in water, adds to its density), and to the consequent production of alcohol, which, on the contrary, by mixture with water, diminishes the density of the compound. The extract, or mucilage, also appears to be in some degree destroyed by fermentation, for the gelatinous consistence of thick liquors is much lessened by this process: the destruction of this principle, however, is by no means so complete as of the sugar, many of the full-bodied ales, for example, retaining much of their original clamminess and gelatinous density even after having undergone a very perfect fermentation.

The acetous fermentation must now be noticed. When any of the vinous liquors are exposed to the free access of atmospheric air, at a temperature of 80° or 85°, they undergo a second fermentation, terminating in the production of a sour liquid called vinegar. During this process, a portion of the oxygen of the air is converted into carbonic acid; hence, unlike vinous fermentation, the contact of the atmosphere is necessary, and the most obvious phenomenon is the removal of carbon from the beer or wine; the vinegar of this country is usually obtained from malt liquor, while wine is employed as its source in those countries where the grape is abundantly cultivated.

Not only do vinous liquors suffer this change,

but every substance susceptible of the vinous can likewise pass into the acetous fermentation; hence, sugar dissolved in water, sweet vegetable juices, or infusions of grains that have been malted, can be converted into vinegar. Fecula, even without the previous process of malting, is equally susceptible of it; for, in the process of starch-making, a quantity of vinegar is formed, not merely from the small portion of saccharine matter in the grain, but likewise, as Vauquelin, in his Analysis of the Sour Liquors of the Starch-Makers, has remarked, froin the fecula itself. Even substances which are not at all susceptible of the vinous fermentation, it appears to be established, may suffer the acetous. This is indeed contrary to an opinion formerly maintained, which regarded the acetous merely as a continuance of the vinots fermentation, and as necessarily preceded by it. But it often happens where the former cannot be traced, and where there is no reason to suppose that it ever did exist, as in vegetable juices or infusions containing much mucilaginous with scarcely any saccharine matter, which soon become sour; and the sourness which even pure mucilage, or a solution of gum in water suffers, is probably owing chiefly to the production of acetous acid.

Nor is pure alcohol, in any state of dilution with water, capable of undergoing the acetous fermentation: there must always be present other vegetable principles, as sugar, mucilage, or farinaceous matter. Even a certain proportion of these is requisite. Hence strong wines do not become so readily sour as weak or sweet wines; for the same reason, wine that has been clarified is less liable to ferment; and strong wines can be made to pass into the acteous fermentation more easily, by adding to them sugar or mucilage; and, when these highly spirituous wines are thus made to ferment, they furnish a much stronger vinegar than those which are weak. Even the vegetable acids appear to contribute to it, and, in the conversion of sweet vegetable juices or of wine into vinegar, there is reason to believe that the malic and tartaric acids they contain are partly changed and pass into the acetic acid.

The addition of some substances which act as ferments, appears also to be requisite. It is true that wine and other fermented liquors will of themselves become sour in a certain time; but this is probably from their containing a portion of matter analogous to ferment, and which excites the change. In preparing vinegar, it is known that a certain quantity of such matter must be added, either a portion of the substance which has been deposited from a liquor that has previously passed into vinegar, or a quantity of yeast; and there is every reason to believe, that it is vegetable gluten which is the essential principal of these ferments. Fourcroy and Vauquelin accordingly found, that, when sugar was added to water which had stood over the gluten of wheat, it quickly formed vinegar; and Berthollet obtained the same result from a mixture of gluten and starch. This principle, Vauquelin remarks, contributes to the formation of vinegar in the liquor formed in the manufacture of starch; and the matter which is contained in

common vinegar from malted grain, and which renders it so liable to putrefaction, is, according to the chemist, vegetable gluten.

The admission of atmospheric air is essential to the acetous fermentation. Hence, wines that are well bottled may be kept for a long time uninjured, and the more free the exposure to the air is, the sooner they become sour. The oxygen of the air is at the same time always absorbed. According to Saussure, this oxygen is not absorbed so as to enter into the composition of the acid, but is expended entirely in abstracting carbon, and of course forming carbonic acid. In keeping wine in contact with oxygen gas for a year in receivers closed with mercury, he found it converted into vinegar; but the diminution of the volume of the gas never exceeded, but was always inferior to the volume of the wine; and hence, acording to the view he gives of the experiment, the oxygen had combined with carbon so as to form carbonic acid, which had been absorbed by the liquor. And accordingly he found, that when he made the experiment with wine previously impregnated with carbonic acid gas, this wine, under the same circumstances, was equally converted into vinegar, but without the volume of the elastic fluid above it being changed; the oxygen consumed being replaced by an equal volume of carbonic acid gas.

A certain degree of temperature is requisite to the acetous fermentation. It takes place slowly, even below 60°; but it proceeds with more rapidity between 60° and 80°; and in forming vinegar artificially, the temperature is kept high. If it fall below 500 it is nearly checked; and hence wines can be longer preserved by being kept below this temperature.

The phenomena which occur in the acetous fermentation are somewhat analogous to those in the vinous. When it is proceeding rapidly, there is an intestine motion, not accompanied, however, with such a disengagement of elastic fluid 28 in the vinous fermentation; the liquor is turbid; its temperature rises; and its smell becomes perceptibly acetous. These appearances at length subside, and the liquor gradually becomes clean, having deposited a kind of glutinous sediment somewhat similar to yeast.

The theory of the acetous fermentation is not yet completely elucidated. Since the strength of the acid which is formed from it is proportioned to the quantity of alcohol, or of matter of a composition analogous to alcohol, and in general capable of passing into it: and, since this alcohol disappears during the fermentation; Lavoisier supposed that the theory of the process might be inferred from the changes which this principle can be supposed to suffer: and, as he found that during the change oxygen is absorbed, while scarcely any sensible quantity of carbonic acid is extracted, he concluded, that the acetous fermentation consists in the oxygenizement of the alcohol. If the experiments of Saussure be admitted as correct, in proving that as much carbonic acid is formed as corresponds with the quantity of oxygen consumed, this acid being retained by the liquor, the theory of Lavoisier would require to be so far modified as to ascribe the change of alcohol into vinegar rather to the abstrac

tion of carbon than the fixation of oxygen; leaving of course, however, a larger proportion of the latter principle in the composition of the acetic acid.

This simple view cannot however be received as altogether just, since alcohol alone cannot undergo this change, nor can it by oxygenizement be converted into acetic acid; and since the presence of mucilage, saccharine matter, or other principles, is always necessary to the acetous fermentation, the operation of which is not explained in conformity to his theory: neither does it explain the action of the ferment which appears to be nearly equally indispensable. It will afterwards appear, that nitrogen probably enters into the composition of acetic acid; and the operation of the ferment may be partly that of affording this element.

Vinegar, the product of the acetous fermentation, is prepared in different countries from different materials. Where the grape is cultivated, it is obtained from weak or spoiled wine. This is kept in a proper temperature with the access of the air, and the fermentation is excited by the addition of a quantity of the sediment of vinegar, of wine already sour, or of the lees of such wine. The product is stronger in proportion to the previous strength of the wine. In this country it is prepared either from unrefined sugars, or from the wort obtained by infusion from malted grain; the fermentation being excited by yeast, and being carried on in a warm apartment. This vinegar is in general inferior in strength and purity to that from wine, and is more liable to become mouldy or suffer the putrefactive fermentation. This appears to be owing chiefly to the presence of glutinous matter; and hence the rationale of the method which Scheele pointed out as the best for preserving vinegar, that of heating it, and bringing it even to boil for a few minutes, the glutinous matter being separated by a kind of coagulation.

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Panary fermentation has already been noticed under the article BREAD, and little more than the theory remains to be examined. Although the fermentation of dough has been termed panary, there is little doubt but it is merely a modification of the acetous. The subjects of both species of fermentation are certainly different, in regard to consistency; but it is probable, that the modification alluded to is the consequence of this difference: for the fermentable matter, from want of room for action, does not arrive at the same point of chemical change which it would do in a more diluted state. We shall not attempt to theorize on the changes which take place during the panary fermentation, fur ther than to suppose that the flour, yeast, and water, give out their elementary components for the formation of saccharine matter, starch, carbonic acid, and acetic acid; and that, during the incipient generation of the latter, the process is stopped by the action of artificial heat.

The fermentation that produces putrefaction is the last stage of this process. The most remarkable changes produced upon a body by putrefaction are upon its color, smell, and taste. Flesh beginning to putrefy, is well known to exhale very soon after a penetrating fetid smell, its color becomes pale, then inclining to blue,

and afterwards livid and black, and its taste nauseous. Transparent liquor, as urine and broth, during putrefaction, becomes also turbid; as the putrefaction advances the smell becomes more and more fetid, and it also acquires great pungency, which is caused by a large quantity of volatile alkali, disengaged from those substances that are completely putrefied. Solid bodies, whilst they are putrefying, swell, become soft, lose the cohesion of their parts, and are lastly reduced to a very disagreeable putrid pulpy mass: the fluids become turbid, and the effluvia are loathsome and sickening, and after a time a putrid gas is disengaged in a slow but sensible effervescence. A foul and brown serum then passes out from the pulpy mass, and about this time the effluvium is very sensibly ammoniacal, which is indicated by its effects on the eyes and throat, and by forming a white vapor with muriatic acid gas. For some time a large part of the putrid substance is evaporated, and carried off in the putrid gas and dispersed in the atmosphere, after which the extreme fetor subsides; and finally the process of putrefaction ceases, and leaves a kind of fat fetid earthy matter. All the gases certainly known to be produced by putrefaction, are carbonic acid, carburetted hydrogen, sulphuretted and phosphuretted hydrogen, and ammonia; but either these, or some of these, must be considerably changed by the solution of the animal matter; or some compound, not yet examined, must be produced in that state of putrefaction, when the gas evolved occasions such dreadful effects upon those that have the misfortune to fall in the way of it, even when diluted considerably with common air. This is said to be the case when the abdomen of a large animal is first burst, the gas from which causes instant fainting, and sometimes death; and even when death does not ensue, it leaves excessive debility and other alarming symptoms for a considerable time. The most deleterious gas that is known is, perhaps, carburetted hydrogen, but the effects of this, as obtained by chemical means, are far short of those above-mentioned, when equally diluted. The generation of ammonia has been satisfactorily accounted for, since the discovery of the constituent parts of the volatile alkali, by the new combination formed between the azote of the animal matter, and the hydrogen, of which latter there are many sources, and particularly that of the decomposition of water. As ammonia is always produced during putrefaction, it seems rational to suppose, that one important purpose of the moisture necessary to the process, is to afford, by its decomposition, the hydrogen of the volatile alkali. The nitrous acid is also an undoubted product of putrefaction; but farther experiments and facts are necessary for explaining the reason why in some cases the azote tends to unite with oxygen to form this acid, and in others with hydrogen to form ammonia.

Every kind of vegetable matter is liable to this species of decomposition: there is none but what ultimately decays, though some resist it, or preserve their composition much longer than others. Those suffer it most quickly which are soluble in water; and any vegetable principle

dissolved in this fluid passes very speedily into it: the surface of the liquor appears covered with a mould: various elastic fluids are disengaged, and at length it is entirely decomposed. Those which are not perfectly soluble, if merely kept humid, present nearly the same results. Oils and resins, which refuse to unite with water or imbibe it, resist any change of this kind for a long period, and can indeed scarcely be said to be subject to it.

The same circumstances favor this species of spontaneous decomposition which favor the others, particularly humidity, and a moderate heat. Any species of vegetable matter, kept perfectly dry, is long in exhibiting any sign of alteration or decay. A certain temperature, which must be less, however, than what will dissipate the humidity, hastens the decomposition, by favoring the approximation and consequent exertion of the affinities of the constituent elements. And the presence of the air often promotes it; at the same time, however, modifying the results.

The gases which are disengaged during this decomposition are of course combinations of the principles of the vegetable substance. According to Saussure junior, they are compounds of hydrogen with carbon, forming inflammable gases and carbonic acid. The former appear principally when the action of the atmosphere is excluded by the substance being immersed under water: the latter is produced when the air is admitted; and its production depends in a great measure on the action of the oxygen of the atmosphere. A portion of water appears also to be formed by the union of part of the oxygen and hydrogen of the vegetable matter.

The principal difference between this species of decomposition and the putrefaction of animal matter is, that there is no evolution of ammonia, or of those fetid combinations which characterise the latter. This is owing to the absence of nitrogen, which is essential to the formation of these. And, accordingly, those varieties of vegetable matter which contain this element, present, in their ultimate decomposition, results extremely similar to those of animal substances: such is particularly the case with all those which contain gluten, and with gluten itself in its pure form.

The residual matter of vegetable substances, after this species of decomposition, frequently contains a large proportion of carbon, especially when formed from those principles in which this element is abundant, as from the ligneous matter; and this may remain long unaltered, the other principles which could re-act upon it having been abstracted in the progress of the decomposition. A residuum of this kind forms that black soft matter which has been named vegetable mould, and which constitutes so important a part of the soil.

When this is obtained free from the undecomposed vegetable matter, more or less mixed with it, it appears from the researches of Saussure, who has particularly examined it, to be nearly uniform in its composition and properties. Subjected to distillation, it gave carburetted hydrogen and carbonic acid gases; water, hold

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