This Commotion and Separation first begins in the whole Substance; for before the Addition of Water, the Subject may remain in dry, solid, and large Pieces, as in Malt, Sugar, &c. which being reduced to Powder, each Grain thereof is an Aggregate of many smaller compound Corpuscles; these being put into Water, dissolve, and separately float therein, till at length, they become so small as to be invisible, and only thicken the Consistence of the Liquor.
These Corpuscles being thus separated from one another, there next ensues a Separation of their component Particles; that is, the Salt, the Oil, and the Earth, are divided by the Interposition of the aqueous Particles.
The first Commotion is no more than a bare Solution; for the saline Particles being easily dissolvable in Water, they are immediately laid hold of by the aqueous Particles, and carried about with them. But the succeeding Separation, or fermentative Motion, is a very different thing; for by this the saline Particles are divided from those of Oil and Earth, partly by the Impulse of the others in their Motion, and partly by the Force of the aqueous Particles, which are now continually meeting and dashing against them.
This Motion is performed by the Water, as a Fluid, or Aggregate of an infinite Number of Particles, in actual and perpetual Motion; their Smallness being proportionable to that of the fermenting Corpuscles, and their Motion, or constant Susceptibility of Motion, by Warmth, and the Motion of the Air, disposing them to move other subtile moveable Corpuscles also. The certain Agreement of Figure, or Size between the aqueous Particles, and those of the Salt in the fermentable Subject, tends greatly to increase this Commotion; for, by this means, they are readily and very closely connected together; and therefore move almost like one and the same compound Corpuscle; whilst the Water is not at all disposed to cohere immediately with either the Oil or Earth. And thus an unequal Concussion is excited in the compound Corpuscles of the fermentable Subject; which Concussion at length strikes out the saline Particle, loosens the others, and finally produces a Separation of the original Connexion of the Subject.
An aqueous Fluid, therefore, is the true, and indeed the only, Instrument for procuring a fermentable Motion in these compound Corpuscles of the Subject: For were an oily Fluid poured upon any fermentable Subject, no vinous Fermentation would ensue; as the Oil could neither give a sufficient Impulse on the compound Corpuscles, which are grosser than its own constituent Particles, nor divide the oily or saline Particles of the Subject from their Connexion with the others, which detain, and, as it were, envelope, or defend them from its Action.
The compound Corpuscles of the fermentable Subject being affected by the perpetual Motion of the Particles of the aqueous Fluid, a proper Degree of Motion is necessary, or that the Particles move with a proper Degree of Velocity, which principally depends on external Heat. A considerable Degree of Cold, indeed, will not absolutely prevent Fermentation, though it will greatly retard it; and a boiling Heat will prevent it still more. A tepid, or middle Degree of Heat between Freezing or Boiling, is therefore the most proper for promoting and quickening the Operation.
The Admission of Air, also, though not of absolute Necessity, yet greatly promotes and quickens the Action, as being a capital Instrument in putting in a proper Degree of Motion the oily Particles of the Subject. But whilst the Air thus contributes to hasten the Effect, it causes at the same time by its Activity some remarkable Alterations in the oily Particles; for it not only moves, but absolutely dissolves and displaces them from their original Connexions; and thus carries them off with itself from the whole Mass. And, therefore, though the Consideration of the Air does not so properly belong to Fermentation in the general, yet it does in particular; as having an accidental Power to alter every Species of this Operation: Consequently its Agency ought to be well understood, either to procure Alterations at pleasure in the fermenting Mass, or to prevent and correct impending Dangers.
The oily Particles thus separated and dissolved by the Air, are also elastic, though they probably derive that Property from their Intercourse with the Air itself, and their being rendered extremely minute.
When, therefore, an aqueous Fluid is added to a fermentable Subject exposed to a temperate Heat, a fermentative Struggle immediately arises, the saline Part of the compound Particles being dissolved by the continual intestine Motion of the Water, and carried up and down with it in all Directions, amidst an infinite Number of other Particles, as well fermentable, as aqueous ones; whence, by this Collision and Attrition, the saline Particles are dissolved, and separated from their Connexion with the oily and earthy. And as the oily Particles are the most subtle and elastic, they would, by this means, be thrown up to the Surface of the Liquor, and carried off by the Air, were they not closely connected with the earthy ones, whose Gravity prevents their Evaporation, and, by coming in contact with others of the same kind, form Aggregations, and sink down, with the oily Particles, to the Bottom. But before these can form a Bulk too large to be supported by the Water, many of the oily Particles are, by their frequent Collisions with the aqueous Fluid, separated from the earthy ones; and, by Degrees, more strongly connected again with the saline ones; whilst, on the other hand, the same saline Particles imbibe some of the earthy ones, which being left single, upon their Separation from the oily Particles, floated about separately in the Fluid.
And hence proceed the several different Consequences of Fermentation; viz. 1. From the Separation of the saline Particles of the fermentable Subject proceeds the tart, saline, or acid Taste of the Liquor; which is more sensible at first, before the Liquor is duly composed and settled, or the due Arrangement and Connection of the saline Particles with those of the oily and earthy Kinds, completed: After which the Liquor proves milder, softer, or less pungent. 2. From the oily Particles being set at liberty, proceeds the strong Smell of the Liquor, and the Head or shining Skin upon the Surface. 3. The earthy Particles collecting together in Clusters, cause the Fluid to appear turbid, and afterwards a visible earthy, or clay-like Matter to be precipitated: And some of the earthy Parts, in their Motion, arriving at the Head, or oily Skin on the Surface, cause it to thicken; and afterwards taking it down along with it, thus constitute the Lees which abound in Oil. 4. From this new Struggle or Collision, which is productive both of Solution, and a new Connection in the saline and earthy Corpuscles, proceeds the Ebullition in Fermentation. And, lastly, by the same repeated Coalition of the oily with the aqueous and saline Particles, the inflammable Spirit is produced.