Abbildungen der Seite

falling to the bottom, and others rising to the proportions cannot be expected, either from top of the Auid. The yeast before mentioned nature working at large, and varying in every is thus separated among other matters, while the climate, soil, and situation, or from our most inbulk of the fluid is materially increased. It is geniously conducted experiments. in this stage that we have the power of regulating A perfect fermentation, therefore, bas been the extent of the fermentation, by separating the considered an object almost impossible to be floating leaven, or allowing it to return into the obtained; and all we wish to show is, that the liquor. Hence, the process of fermentation in errors of the mixture may be corrected, and the a full cask, ejecting that substance by the bung- whole process improved, by good management. hole.

The common practice, until a few years back, The disengaged gas is carbonic acid chiefly; has been to ferment in open vessels ; and though but holding some alcohol in solution. It ap- it was a circumstance well known among chepears, by analysis, that this is the produce of mists, that a certain portion of spirit and favor part of the carbon of the sugar and of its oxygen; escaped in the form of vapor during the process, and this is the great change which leads to the yet no one had an idea that the condensatory production of the alcohol. But it also contains system could be applied, as it appeared imsome obscure vegetable matter in suspension; possible to effect the fermentation in air-tight because, if passed through water, it not only vessels, being unable to surmount the great converts it into vinegar, but deposits that muci- difficulty which existed of keeping down and lage, which, in vinegar, is called the mother. It managing that enormous bulk of non-conis possible, however, that this may itself be a densable gases, which are emitted during the new compound : and it is one which, in certain decomposition of the saccharine matter, and cases, contains azote.

which acquire greater expansive force by the All those juices of fruits which undergo the gradual increase of heat. vinous fermentation, either with or without the The idea, however, occurred to Madame Geraddition of sugar, contain an acid. Vegetable vais, that distillation might be carried on during acids are obtained chiefly from fruits. The the fermenting process. Having come to this apple, for instance, contains malic acid ; the le- conclusion, she proceeded to construct an appamon, citric acid ; the grape, tartaric and malic ratus that would operate in such manner as to acids. The marquis de Bouillon has ascertained return into the vessel the spirit and the flavor that must will not ferment if all the tartar which that was evolved from the fermenting gyle, and it contains be separated from it; but it ferments let out the non-condensable gases, which might, perfectly well on restoring that salt. The same by the increasing heat, acquire too great an chemist ascertained that the strength of wine is expansive force, and burst the working-tun. A considerably increased by adding tartar and short description of this apparatus will be sugar to the must. We may conclude from these a fresh proof that the greatest advantages are facts that the presence of a vegetable acid is of often derived from the most simple means. importance in these spontaneous fermentations. It consists of a vessel resembling the head of It deserves attention, that Bouillon obtained more the ancient still, and constructed of such form tartar from verjuice than from wine; and he ob- as to be capable of being placed securely on the served, that the more the proportion of sugar in back, or vat, in which the process of fermentation grapes increased, the more that of tartar dimi- is to be carried on; the back or vat must be nished.

closed air-tight, with a hole in the top, commuIt seems more than probable, from the expe- nicating with that part of the apparatus called riments of Bouillon and Chaptal, that the tartaric the cone, or condenser This cone is surrounded acid is partly decomposed during the fermenta- by a cylinder or reservoir, which is to be filled tion, and that a portion of malic acid is formed. with cold water, so that the alcoholic vápor, or The process, therefore, is more complicated than steam, evolved during the process, may be conwas suspected by Lavoisier. It is obviously densed as it comes in contact with the cold inanalogous to combustion, as is evident from the terior surface of the cone; and, being thereby evolution of caloric and the formation of car- converted into a liquid, trickles down the inside bonic acid, which is a product of combustion. of the condenser, and tlırough a long pipe is reProust has ascertained that, during the fermenta- turned into the fermenting liquor. tion, not only carbonic acid, but azotic gas also, By the application of this apparatus, a conis disengaged. This is a demonstration, that all siderable portion of alcohol, which has been the constituents of must are concerned ; for bitherto suffered to escape in the form of vapor, sugar does not contain that principle. Thenard along with the non-condensable gases, is concould detect no azote in the carbonic acid from densed and returned into the liquor; and the wort.

non-condensable gases are carried off by a pipe, We have already seen that a rinous fer- which, proceeding from the interior lower part mentation, to be perfect, requires very exact of the cone, and running up the inside of the proportions of mucilage and saccharine matter, cylinder in the cold water, passes out through so as to have the one just sufficient to destroy or the side, and the end is immersed some depth attenuate the other; in which case the result below the surface of water contained in a separate will be, if the operation has been properly con- vessel, permitting the gases to escape, but still ducted, a mixture of alcohol and water, differ- under a certain degree of pressure, the object of ently flavored, according to the materials from which is to confine the alcoholic steam and gas which it is produced, as grapes, pears, apples, within the cone, and allow them a sutticieni turne or malt and hops; but such accuracy in the to cool and condense.

[merged small][merged small][merged small][ocr errors]

To obtain a good fermentation, as complete a from the fermenting gyle, the atmospheric air, decomposition of the must or wort, and as per- being lighter, is driven out from the upper part feet a recomposition of alcohol as possible, are of the working tun; and, as no air is permitted the great objects to be obtained. To acquire the to enter afterwards, all the subsequent carbonic former, three requisites are necessary—Huidity, acid gas emitted, diminishes the quantity of heat, and motion ; the latter-density, coolness, oxygen contained in the gyle, by the oxygen and tranquillity.

uniting with the carbon as fast as it disunites Let us examine each of these separately; first, from the saccharine matter during its decompoof Auidity.

sition, and thereby secures a soundness and The specific gravity of the liquid most eligi- peculiar mildness, not to be procured by any ble to produce a good fermentation, is between other mode. 1.020 and 1:140, or eighteen, and 132 pounds The necessary conditions for a complete deby Dicas's improved saccharometer, made by composition of the saccharine matter having Joseph Long. Below eighteen pounds of real been stated, it remains to notice those required extract per barrel, the liquid is too thin to pro- for a good production of alcohol. duce a proper fermentation, and above 132 The first already mentioned is a certain denpounds it is too thick; but, supposing the speci- sity, in order to allow the several principles hc gravity of the must or wort to be correct, it which are disunited to recombine. It is doubtmay be carried beyond a proper dilatation by ful whether such a combination will in any case too much heat, or congealed to too great a con- take place, until the temperature of the gyle, sistency by excessive cold; consequently either having attained its greatest heat, is afterwards a thunder-storm or hard frost will derange the cooled a few degrees; a fact confirming which is, operation, and are equally injurious to fermen- that a portion of the liquid taken out when at its tation. Any method, therefore, that will ensure greatest heat, and tried by distillation, produced an even temperature must be of great import- little or no spirit; but such refrigeration must ance ; and such a method is obtained by apply- not be effected too suddenly, as it might coaguing the apparatus already described, since, hy late the yet undecomposed mucilage, and check preventing the access of atmospheric air, the its further action on the remaining saccharine sudden changes of the external temperature can matter; and by arresting that natural operation have no effect upon the fermenting syle; and if which ought to be pursued a longer or shorter it has been commenced at a proper heat (which period, according to the specific gravity of the is between sixty-five and eighty), will proceed fermentable matter, might produce that result through its different stages, as well during the termed 'ropiness,' by holding in solution the coahottest days of summer, as in the selected months gulated mucilage. of autumn and spring.

Ilere again the apparatus will be found of With respect to motion, we are indebted to great service, for, by frequently renewing the M. Gay Lussac, as we have already stated, for a cold water in its reservoir, the internal temperabeautiful and important experiment, proving ture will gradually diminish by the heat of the that must, possessed of all the requisites to pro- gyle coming in contact with the cold interior of dace a good fermentation, will not begin to fer- the cone: but, in order to effect this, the tranment unless excited by a foreign agent. He quillity above mentioned is necessary, since the placed the must in a close vessel, from which continual motion is caused by the oxygen solithe atmospheric air had been exhausted, where citing new combinations with the carbon, and it remained several days without giving any thereby constantly giving rise to a fresh supply signs of fermentation, from which he concluded of heat. some power was wanting to break the union of Besides the advantages already mentioned, its constituent principles; he therefore introduced which are common to all fermented liquors, a small quantity of oxygen, which immediately there are others peculiar to each, that require to caused the must to ferment, evidently proving be explained. the necessity of a small portion of atmospheric The apparatus being applied to ferment the air (which contains oxygen), to allow the fermen- must of grapes, has been found to procure an tation to commence. But it at the same time increase of quantity, amounting in some instanproves, that, after performing that office, this ces to ten or twelve per cent., and which necesgreat enemy to all fermented liquors may be dis- sarily varies according to situation, season, or pensed with, without impeding the process; as former management; but in no instance has it the small quantity of oxygen, introduced by M. been found less than from five to six per cent. Gay Lussac, was soon absorbed by the carbon When applied to the fermentation of beer, to form carbonic acid gas, and he found no oc- this saving has constantly been between four and casion for any further supply:

a half and five per cent., a quantity certainly inThis discovery is of the greatest importance, ferior to that obtained from wine, but which will since it enables us, without the least detriment not appear unimportant when it is considered or inconvenience to the process, to exclude the that this saving is a spirit congenial to the nature oxygen of atmospheric air, which, by constantly of the beer, and an essential oil necessary to its supplying the gyle with the principle that causes preservation ; in addition to the peculiar mildand promotes acidity, casts on it from the first ness and superior flavor. that roughness and disagreeable flavor which Mr. Henry found, by a series of very interestspoil most of our common beverages.

ing experiments, that malt infusion might be Here again the new apparatus proves of great made to enter into complete fermentation by benefit

, for, as soon as carbonic acid gas is evolved impregnating it with carbonic acid, prepared Vor. IX.


from chalk and sulphuric acid, and the liquor but every substance susceptible of the vinous thus fermented gave a yeast which made per- can likewise pass into the acetous fermentation ; fect bread, gave alcohol by distillation, and hence, sugar dissolved in water, sweet vegetable vinegar by further keeping. The wort' itself juices, or infusions of grains that have been undoubtedly contained all the ingredients of malted, can be converted into vinegar. Fecula, yeast, since this substance was produced during even without the previous process of malting, is the fermentation; but the experiment is decisive equally susceptible of it; for, in the process of to prove that no addition of azotic extract is re- starch-making, a quantity of vinegar is formed, quired to begin fermentation in materials naturally not merely from the small portion of saccharine fermentable, though, when once begun, the yeast, matter in the grain, but likewise, as Vauquelin, as fast as it was produced, must have assisted in in his Analysis of the Sour Liquors of the the fermentation then going on. The evidence Starch-Makers, has remarked, froin the fecula for the necessity of an acid to begin fermentation itself. Even substances which are not at all is, therefore, more decisive, but it is still doubt- susceptible of the vinous fermentation, it appears ful whether any particular one is required, or to be established, may suffer the acetous. This whether there are not several which will answer is indeed contrary to an opinion formerly mainthe purpose. In Mr. Henry's experiments the tained, which regarded the acetous merely as a acid employed was the carbonic, and, from the continuance of the vinous fermentation, and as arrangement of the apparatus, probably a small necessarily preceded by it. But it often happens portion of sulphuric was also carried'in along where the former cannot be traced, and where with it. But in grape juice there is no proof of there is no reason to suppose that it ever did exist, the existence of carbonic acid ready formed, as in vegetable juices or infusions containing though the tartaric, malic, and other vegetable much mucilaginous with scarcely any saccharine acids contain within themselves the ingredients matter, which soon become sour; and the sonrof carbonic acid, and are chiefly and ultimately ness which even pure mucilage, or a solution of resolvable into this acid. Yeast will ever induce gum in water suffers, is probably owing chiefly fermentation after it is pressed and dried into to the production of acetous acid. solid cakes (a practice not uncommon, as it will Nor is pure alcohol, in any state of dilution keep for a great length of time in this form), with water, capable of undergoing the acetous but after this operation it can hardly contain any fermentation: there must always be present carbonic acid ready formed, though with abun- other vegetable principles, as sugar, mucilage, or dant tendency to reproduce it by the first mutual farinaceous matter. Even a certain proportion action of its constituent parts.

of these is requisite. Hence strong wines do The attenuation of liquors, or the diminution not become so readily sour as weak or sweet of their specific gravity by fermentation, is very wines ; for the same reason, wine that has been striking. This is shown by the hydrometer, clarified is less liable to ferment; and strong which swims much deeper in fermented liquor, wines can be made to pass into the acteous ferthan in the same materials before fermentation. mentation more easily, by adding to them sugar Much of this attenuation is, doubtless, owing to or mucilage ; and, when these highly spirituous the destruction of the sugar, (which, dissolved in wines are thus made to ferment, they furnish a water, adds to its density), and to the consequent much stronger vinegar than those which are production of alcohol, which, on the contrary, weak. Even the vegetable acids appear to conby mixture with water, diminishes the density · tribute to it, and, in the conversion of sweet of the compound. The extract, or mucilage, alsó vegetable juices or of wine into vinegar, there is appears to be in some degree destroyed by fermen- reason to believe that the malic and tartaric tation, for the gelatinous consistence of thick acids they contain are partly changed and pass liquors is much lessened by this process: the into the acetic acid. destruction of this principle, however, is by no The addition of some substances which act means so complete as of the sugar, many of the as ferments, appears also to be requisite. It is full-bodied ales, for example, retaining much of true that wine and other fermented" liquors will their original clamminess and gelatinous density of themselves become sour in a certain time; even after having undergone a very perfect fer- but this is probably from their containing a pormentation.

tion of matter analogous to ferınent, and which The acetous fermentation must now be noticed. excites the change. În preparing vinegar, it is When any of the vinous liquors are exposed to known that a certain quantity of such matter the free access of atmospheric air, at a temper- must be added, either a portion of the substance ature of 80° or 85°, they undergo a second fer- which has been deposited from a liquor that has mentation, terminating in the production of a previously passed into vinegar, or a quantity of sour liquid called vinegar. During this pro- yeast; and there is every reason to believe, that cess, a portion of the oxygen of the air is con- it is vegetable gluten which is the essential verted into carbonic acid; hence, unlike vinous principal of these ferments.

Fourcroy and fermentation, the contact of the atmosphere is Vauquelin accordingly found, that, when sugar necessary, and the most obvious phenomenon is was added to water which had stood over the the removal of carbon from the beer or wine; gluten of wheat, it quickly formed vinegar; and the vinegar of this country is usually obtained Berthollet obtained the same result from a mixfrom malt liquor, while wine is employed as its ture of gluten and starch. This principle, Vausource in those countries where the grape is quelin remarks, contributes to the formation of abundantly cultivated.

vinegar in the liquor formed in the manufacture Not only do vinous liquors suffer this change, of starch; and the matter which is contained ja

[ocr errors][ocr errors]

common vinegar from malted grain, and which tion of carbon than the fixation of oxygen ; leaving renders it so liable to putrefaction, is, according of course, however, a larger proportion of the latter w the chemist, vegetable gluten.

priuciple in the composition of the acetic acid. The admission of atmospheric air is essential This simple view cannot however be received to the acetous fermentation. Hence, wines that as altogether just, since alcohol alone cannot are well bottled may be kept for a long time un- undergo this change, nor can it by oxygenizement injured, and the more free the exposure to the be converted into acetic acid; and since the preair is, the sooner they become sour. The oxygen sence of mucilage, saccharine matter, or other of the air is at the same time always absorbed. principles, is always necessary to the acetous According to Saussure, this oxygen is not ab- fermentation, the operation of which is not exsorbed so as to enter into the composition of the plained in conformity to his theory: neither does acid, but is expended entirely in abstracting it explain the action of the ferment which apcarbon, and of course forining carbonic acid. pears to be nearly equally indispensable. It In keeping wine in contact with oxygen gas for will afterwards appear, that nitrogen probably a year in receivers closed with mercury, he found enters into the composition of acetic acid; and it converted into vinegar; but the diminution of the operation of the ferment may be partly that the volume of the gas never exceeded, but was of affording this element. always inferior to the volume of the wine; and Vinegar, the product of the acetous fermentahence, acording to the view he gives of the ex- tion, is prepared in different countries from difperiment, the oxygen had combined with carbon ferent materials. Where the grape is cultivated, so as to form carbonic acid, which had been ab- it is obtained from weak or spoiled wine. This is sorbed by the liquor. And accordingly he found, kept in a proper temperature with the access of that when he made the experiment with wine the air, and the fermentation is excited by the previously impregnated with carbonic acid gas, addition of a quantity of the sediment of vinegar, this wine, under the same circumstances, was of wine already sour, or of the lees of such wine. equally converted into vinegar, but without the The product is stronger in proportion to the volume of the elastic fuid above it being previous strength of the wine. In this country it is changed; the oxygen consumed being replaced prepared either from unrefined sugars, or from by an equal volume of carbonic acid gas. the wort obtained by infusion froin malted

A certain degree of temperature is requisite grain ; the fermentation being excited by yeast,
to the acetous fermentation., It takes place and being carried on in a warm apartment.
slowly, even below 60°; but it proceeds with This vinegar is in general inferior in strength
more rapidity between 60° and 80°; and in and purity to that from wine, and is more liable
forming vinegar artificially, the temperature is to become mouldy or suffer the putrefactive fer-
kept high. If it fall below 500 it is nearly mentation. This appears to be owing chiefly to
checked; and hence wines can be longer pre- the presence of glutinous matter; and hence the
served by being kept below this temperature. rationale of the method which Scheele pointed

The phenomena which occur in the acetous out as the best for preserving vinegar, that of
fermentation are somewhat analogous to those in heating it, and bringing it even to boil for a few
the vinous. When it is proceeding rapidly, there minutes, the glutinous matter being separated by
is an intestine niotion, not accompanied, how- a kind of coagulation.
ever, with such a disengagement of elastic fluid Panary fermentation has already been noticed
2 in the vinous fermentation; the liquor is under the article Bread, and little more than
turbid; its temperature rises; and its smell be- the theory remains to be examined. . Although
comes perceptibly acetous. These appearances the fermentation of dough has been termed pa-
at length subside, and the liquor gradually ve- nary, there is little doubt but it is merely a mo-
comes clean, having deposited a kind of glutin- dification of the acetous. The subjects of both
aus sediment somewhat similar to yeast. species of fermentation are certainly different, in

The theory of the acetous fermentation is not regard to consistency; but it is probable, that
yet completely elucidated. Since the strength of the modification alluded to is the consequence
the acid which is formed from it is proportioned of this difference: for the fermentable matter,
to the quantity of alcohol, or of matter of a compo- from want of room for action, does not arrive at
sition analogous to alcohol, and in general capable the same point of chemical change which it
of passing into it: and, since this alcohol disap- would do in a more diluted state. We shall
pears during the fermentation ; Lavoisier sup- ot attempt to theorize on the changes which
posed that the theory of the process might be take place during the panary fermentation, fur
inferred from the changes which this principle can ther than to suppose that the flour, yeast, and
be supposed to suffer : and, as he found that water, give out their elementary components for
during the change oxygen is absorbed, while the formation of saccharine matter, starch, car-
Searcely any sensible quantity of arbonic acid is bonic acid, and acetic acid; and that, during the
extracted, he concluded, that the acetous fermen- incipient generation of the latter, the process is
tation consists in the oxygenizement of the al- stopped by the action of artificial heat.
cohol. If the experiments of Saussure be ad- The fermentation that produces putrefaction
mitted as correct, in proving that as much car- is the last stage of this process. The most re-
bonic acid is formed as corresponds with the markable changes produced upon a body by
quantity of oxygen consumed, this acid being re- putrefaction are upon its color, smell, and taste.
tained by the liquor, the theory of Lavoisier would Flesh beginning to putrefy, is well known to
require to be so far modified as to ascribe the exhale very soon after a penetrating fetid smell,
change of alcohol into vinegar rather to the abstrac- its color becomes pale, then inclining to blue,





and afterwards livid and black, and its taste dissolved in this fluid passes very speedily into

Transparent liquor, as urine and it: the surface of the liquor appears covered broth, during putrefaction, becomes also turbid; with a mould: various elastic fluids are disenas the putrefaction advances the smell becomes gaged, and at length it is entirely decomposed. more and more fetid, and it also acquires great Those which are not perfectly soluble, if merely pungency, which is caused by a large quantity kept humid, present nearly the same results

. of volatile alkali, disengaged from those sub- Oils and resins, which refuse to unite with water stances that are completely putrefied. Solid or imbibe it, resist any change of this kind for a bodies, whilst they are putrefying, swell, become long period, and can indeed scarcely be said to soft, lose the cohesion of their parts, and are be subject to it. lastly reduced to a very disagreeable putrid The same circumstances favor this species of pulpy mass: the fluids become turbid, and the spontaneous decomposition which favor the effluvia are loathsome and sickening, and after a others, particularly humidity, and a moderate time a putrid gas is disengaged in a slow but heat. Any species of vegetable matter, kept sensible effervescence. A foul and brown serum perfectly dry, is long in exhibiting any sign of then passes out from the pulpy mass, and about alteration or decay.

A certain temperature, this time the effluvium is very sensibly aınıno- which must be less, however, than what will niacal, which is indicated by its effects on the dissipate the humidity, bastens the decomposieyes and throat, and by forming a white vapor tion, by favoring the approximation and consewith muriatic acid gas. For some time a large quent exertion of the affinities of the constituent part of the putrid substance is evaporated, and elements. And the presence of the air often carried off in the putrid gas and dispersed in the promotes it; at the same time, however, modiatmosphere, after which the extreme fetor sub- fying the results. sides; and finally the process of putrefaction The gases which are disengaged during this ceases, and leaves a kind of fat fetid earthy decomposition are of course combinations of the matter. All the gases certainly known to be principles of the vegetable substance. Accordproduced by putrefaction, are carbonic acid, ing to Saussure junior, they are compounds of carburetted hydrogen, sulphuretted and phosphu- hydrogen with carbon, forming inflammable retted hydrogen, and ammonia; but either these, gases and carbonic acid.

The former appear or some of these, must be considerably changed principally when the action of the atmosphere by the solution of the animal matter ; or some is excluded by the substance being immersed compound, not yet examined, must be produced under water: the latter is produced when the in that state of putrefaction, when the gas evolved air is admitted ; and its production depends in a occasions such dreadful effects upon those that great measure on the action of the oxygen of the have the misfortune to fall in the way of it, even atmosphere. A portion of water appears also to when diluted considerably with common air. be formed by the union of part of the oxygen This is said to be the case when the abdomen and hydrogen of the vegetable matter. of a large animal is first burst, the gas from The principal difference between this species which causes instant fainting, and sometimes of decomposition and the putrefaction of animal death; and even when death does not ensue, matter is, that there is no evolution of ammonia, it leaves excessive debility and other alarming or of those fetid combinations which characterise symptoms for a considerable time. The most the latter. This is owing to the absence of deleterious gas that is known is, perhaps, nitrogen, which is essential to the formation of carburetted hydrogen, but the effects of this, as these. And, accordingly, those varieties of vegeobtained by chemical means, are far short of those table matter which contain this element, present, above-mentioned, when equally diluted. The in their ultimate decomposition, results extremely generation of ammonia has been satisfactorily similar to those of animal substances : such is accounted for, since the discovery of the consti- particularly the case with all those which contuent parts of the volatile alkali, by the new com- tain gluten, and with gluten itself in its pure bination formed between the azote of the animal form. matter, and the hydrogen, of which latter there The residual matter of vegetahle substances, are many sources, and particularly that of the after this species of decomposition, frequently decomposition of water. As ammonia is always contains a large proportion of carbon, especially produced during putrefaction, it seems rational when formed from those principles in which to suppose, that one important purpose of the this element is abundant, as from the ligneous moisture necessary to the process, is to afford, matter; and this may remain long unaltered, the by its decomposition, the hydrogen of the volatile other principles which could re-act upon it alkali

. The nitrous acid is also an undoubted having been abstracted in the progress of the product of putrefaction ; but farther experiments decomposition. A residuum of this kind forms and facts are necessary for explaining the reason that black soft matter which has been pamed why in some cases the azote tends to unite with vegetable mould, and which constitutes so inoxygen to form this acid, and in others with hy- portant a part of the soil. drogen to form ammonia.

When this is obtained free from the undeEvery kind of vegetable matter is liable to composed vegetable matter, more or less mixed this species of decomposition: there is none with it, it appears from the researches of Sausbut what ultimately decays, though some resist sure, who has particularly examined it, to be it, or preserve their composition much longer nearly uniform in its composition and properthan others. Those suffer it most quickly which ties. Subjected to distillation, it gave carburetted are soluble in water; and any vegetable principle hydrogen and carbonic acid gases; water, hold

« ZurückWeiter »