A similar want of perfection to that observed in wines, may be noticed in our beers and ales, and it chiefly has its origin in the different degrees of heat the malt has been impressed with, both in drying and extracting; where, in the processes of malting and brewing, a sufficient heat has not been maintained, the liquor undoubtedly must become acid; in proportion as the contrary is the case, or that the beer is overcharged with hops, if this is in no great excess, it retains still a greater tendency to fermentation than to putrefaction, acids not being wanting, but only enveloped. In this case, time will get the better of the disease; like to the wines made from the growth of too hot a sun, these liquors, at a certain period, sicken, smell rancid, and have a disagreeable taste, but, by long standing, they begin to fret, and, receiving more acids from the air, recover their former health, and improve in taste.
But should the quantity of oils exceed this last proportion, in wines formed from corn, the must, instead of fermenting, would putrify, even though, by some means, elastic air has been driven into them. In this case, the over proportion of the oil, and its tenacity, prevents the entrance of the acids, the wort receives no enlivening principle from without, and the air, at first conveyed into it, is enveloped with oils so tenacious as to be incapable of action. Nothing so much accelerates putrefaction as heat, moisture, and a stagnating air; and all substances corrupt, sooner or later, in proportion to the inactivity of the contained air, to the want of a proper vent, and to the closeness of their confinement. Besides these cases, beers and ales, as well as wines, sometimes are vapid and flat, without being sour; this does not so much arise from the imbibing the air of the atmosphere, as from their fermenting, generating and casting off too much air of their own. To prevent this accident, they are best preserved in cool cellars, where their active invigorating principles are kept within due bounds, and not suffered to fly off. These facts ought to convince us of the truth, deduced by Dr. Hales, from many experiments, that there is a great plenty of air incorporated in the substance of vegetables, which, by the action of fermentation, is roused into an elastic state, and is as instrumental to produce this act, as it is necessary to the life and being of animals.
I should here close this short and imperfect account; but as, in the art of brewing, there is no part so difficult, and at the same time so important to be in some measure understood, as the cause and effects of fermentation; and as the examination of this act, in all the different lights in which it offers itself to our notice, can hardly be thought uninteresting, these few detached thoughts I hope will be allowed of.
The effect of the act of fermentation on liquors is, so to attenuate the oils; as to cause them to become spiritous, and easily inflammable. When a wine is dispossessed of such oils, which is nearly the case in vinegar, far from possessing a heating or inebriating quality, it refreshes and becomes a remedy against intoxication. The term of fermentation ought, perhaps, only to be applied to that operation which occasions the expressed juices of vegetables to become wine: but as several acts have assumed the same name, it may not be improper here to notice the difference between them.
Vegetation, one of them, is that operation of nature wherein more air is attracted than repelled. I believe all that has been said above, concerning the juice of grapes, is a convincing proof thereof.
Fermentation is, where the communication of the external and internal air of a must is open, and in a perfect state; when the power of repelling, is equal to that of attracting, air.
Putrefaction is when, by the power of strong oils, or otherwise, the communication between the external and the internal air of the must is cut off, so that the liquor neither attracts the one nor repels the other, but, by an intestine motion, the united particles separate and tend to fly off.
Effervescence is when, by the power of attraction, the particles of matter so hastily rush into contact, as to generate a heat which expels the enclosed air; and this more or less in proportion to the motion excited.