FERMENTATION.

463

sngar, and from the evaporation of the fluid a starchy sirup will be obtained, entirelysimilar to that procurable by the action of very dilute sulphuric acid upon starch.

f he substance which operates this saccharine change, or the appropriate yeast of thesugar fermentation, which had been previously imagined to be a residuum of gluten orVegetable albumen in the germinated grain, has been traced by Payen and Persoz to aPeculiar proximate vegetable principle called by them diastase. This substance is gen-® r ated during the germination of barley, oats, and wheat, and may be obtained separatelyy infusing the ground malt in a small quantity of cold water, straining oil' the liquor,isro ®hering it, and heating the clear solution in a water-bath to the temperature of® F. The greater part of the vegetable albumen is thus coagulated, and must be,^P arat £d by a fresh filtration; the liquid is afterwards treated with alcohol as long ase nocculent precipitate of diastase falls. In order to purify it still more completelyb the azotized matter, it may be once more dissolved in water, and again precipitated5 alcohol. When dried at a low temperature, it appears as a white solid, which con-It ‘H ti° azote, is insoluble in strong alcohol, but dissolves in weak alcohol and water.0r , s °mtion is neutral and tasteless ; and if left to itself, it changes spontaneously, soonerfro * ter ’ accor| ling to the degree of warmth, and becomes sour. At the temperature of149° to 168°, it has the property of converting starch into gum or dextrine, andcat^m an ^’ w hen sufficiently pure, it does this with such energy, that one part of it isits" ab * e saccharifying 2000 parts of dry starch. It acts the more rapidly the largerhe Fj 0 P or ^°a. Whenever the solution of diastase with starch or dextrine has beenh 9 to the boiling point, it loses the property of transforming these substances. One2 °^ Parts of well malted barley appear to contain about one part of this new body.tj 0 ‘ .Vinous Fermentation. —In this fermentation the sugar existing in watery solu-®ent' S, f >y the operation of the ferment or yeast, converted into alcohol, with disengage-. °‘ earbonic acid gas. If we dissolve one part of pure sugar in ten parts of water,able t^r 6 t * le so ^ ul i° n lu a temperature of from 68° to 77° F., which is that most favor-ye ast ° f) * ermenta ti on , it will remain unaltered. But if we stir into that solution some beer^°nic' ■ Phenomena of fermentation soon appear in the above circumstances ; for car-ternn * cid * s evolved, with intestine movements of the liquid, and an increase of itstll Ptu rature \ A body of yeast rises to the surface, and exhibits a continual formation andtn 0 (i 0 „ e °‘ a i r bubbles. At length the sugar being in a great measure decomposed, thealcohof Cease > the liquor becomes clear, and instead of being a sirup, it is now a diluteatul of ’ Tl ! e yeast has by this time fallen to the bottom in a somewhat compact form,Provja ^ whitish color, deprived of the property of exciting fermentation in fresh sirup,Ejp er j n ° ur| due excess of it was added at first, for that alone would remain effective.’ a tion s ' 10ws that for the conversion of a determinate quantity of sugar by fermen-1| p e ’ a determinate quantity of yeast is necessary, which has been estimated at about<ic finit e Cent ' ' a the dry state. When the yeast has been decomposed by fermenting itss <i?a r l >r ?r’ ort ' on of sugar, it loses its fermentable property, and leaves thj excess of; be 'tpa n SS! d > formin ? a sweet vinous solution. The same thing happens if the yeast* ate stine a e . rom the wort by a filter in the progress of the fermentation, for then allIti ^ motion speedily stops, although much saccharine matter remains,tinted wi . Jai f s sweet fruits, of grapes, for example, the ferment is intimately asso-atnio spher thesu S ar - H I s at first soluble and inactive, till it absorbs oxygen from theS ° as to n r e ’ ' Viler!>1) y It becomes an operative ferment, but, at the same time, insoluble,? r JKUsl j eci P lta te at the end of the process. When the expressed juice of the grape,“oiling wat enca>se d iu a vessel out of contact of air, and there subjected to the heat of:®*Peri eilBe er> V- 1 '' sma il portion of oxygen present is rendered inactive, and the liquor°f oxyg en no fermentative change. If the grapes be squeezed in an atmosphere deprivedMessed g r ’ a . confined in the same, the juice will also remain unaltered. Recently ex-Se Parati on J ulce is .limpid, and manifests the commencement of fermentation by the

ration h.° the yeasl y * ' ‘ ‘ -

t “ rrr >ent „ turbid after a certain time, gas begins to be evolved, and the separate!

tar Ihe Ves ^°f es t * le sugar. At the end of the process the yeast collects at the bot-'p* 1 ° a ; and a„ Se ’ usua 'ly in larger quantity than was sufficient to complete the fermen*® f^mentati” 66 a cons iderable portion of it possesses still the fermentative faculty...„ Ve dand fl 0 a( 1 i„ lbae ^’,. w k en °nee begun, that is, whenever the yeasty particles are

> is ther

a Ponth P e r

r substance, which can take place only with access of air. The

suSe n r • for Which evolution a very minute quantity

•ts i, l ’ ls thenceforth independent of the contact of air, and „ oes j .

vm„ la .°P ea vessels; so that the production of alcohol and carbonic acid depends sole ymutual reaction of the ferment and the sugar.

w.~— a - '

. 'I'he

.. oi tie ferment and the from a fine ‘ nf “^°" 0 ^bk, a gummy,

stat“ e J east > wMch may be obtained tolerably P water to separate fb consi'-

state of fermentation, after being washed with e'»> folds of and smell,

aad saccharine matter, and after being P resse l b ^ c destitute of both tas ^ bolU „g

‘Wes a pulverulent, grayish yellow, g ranalar dfeolves, indeed, only Too’

'“soluble both in water and alcohol. Cold water dissoiwater very little more.