Experience has demonstrated, that all Ferments abound much more in essential Oil, than the Liquor which produced them; and consequently they retain, in a very high Degree, the Smell and Flavour of the Subject. It is therefore requisite, before the Ferment is applied, to consider what Flavour is intended to be introduced, or what Species of Ferment is most proper for the Liquor.
The Alteration thus caused by Ferments is so considerable, as to render any neutral fermentable Liquor, of the same Flavour with that which yielded the Ferment. This Observation is of much greater Moment than will presently be conceived; for a new Scene is hereby opened, both in the Business of Distillation, and others depending upon Fermentation. It must, however, be observed, that its Benefit does not extend to Malt, treated in the common Method; nor to any other Subject but what affords a Spirit tolerably pure and tasteless: For, otherwise, instead of producing a simple, pure, and uniform Flavour, it causes a compound, mixed, and unnatural one. How far the fine Stiller may profit by it, well deserves his Attention; and whether our native Cyder Spirit, Crab Spirit, &c. which have very little Flavour of their own, may not, by this Artifice, be brought nearly, if not intirely, into the State of some foreign Brandies, so highly esteemed, is recommended to Experience.
It is common with Distillers, in order to increase the Quantity of Spirit, give it a particular Flavour, or improve its Vinosity, to add several things to the Liquor, during the Time it is in a State of Fermentation; and these Additions may properly be reduced to Salts, Acids, Aromatics, and Oils.
All rich vegetable Juices, as Treacle, Honey, &c. which either want a natural Acid, have been deprived of it, or contain it in too small a Quantity, will be greatly improved by adding, at the Beginning of the Operation, a small Quantity of the vegetable or fine mineral Acids; as Oil of Sulphur, Glauber’s Spirit of Salt, Juice of Lemons, or an aqueous Solution of Tartar. These Additions will either give, or greatly improve the vinous Acidity of the Subject, but not increase the Quantity of the Spirit, that Intention being performed by Aromatics and Oils.
All pungent Aromatics have a surprising Quality of increasing the Quantity of the Spirit, as well as in altering, or improving the Flavour; but their Use requires that the Fermentation should be performed in close Vessels. And if a large Quantity be intended to be added, Care must be taken not to do it all at once, lest the Oiliness of the Ingredients should check the Operation. But if the Flavour be the principal Intention, they should not be added till the Operation is nearly finished. After the same Manner a very considerable Quantity of any essential vegetable Oil may be converted into a surprisingly large Quantity of inflammable Spirit; but great Caution is here also necessary not to drop it too fast, or add too large a Quantity at a time, which would damp the Fermentation; it being the surest Method of checking, or totally stopping this Operation, at any Point of Time required. The best Method, therefore, of adding the Oil, so as to avoid all Inconveniencies, is to rub the Oil in a Mortar with Sugar, which the Chemists call making an Olæosaccharum, by which Means the Tenacity of the Oil will be destroyed, and the whole readily mix with the Liquor, and immediately ferment with it. The Distiller would do well to consider these Observations attentively, as he may thence form an advantageous Method of increasing the Quantity of Spirits, and at the same Time greatly improve their Quality and Flavour.
But in order to put these Observations in practice, particular Regard must be had to the containing Vessel in which the Fermentation is performed, the Exclusion of the Air, and the Degree of the external Heat or Cold.
With regard to the containing Vessel; its Purity, and the Provision for rendering it occasionally close, are chiefly to be considered. In cleansing it, no Soap, or other unctuous Body should be used, for fear of checking the Fermentation; and, for the same Reason, all strong alkaline Lixiviums should be avoided. Lime-water, or a turbid Solution of quick Lime may be employed for this Purpose, without producing any ill Effect; it will also be of great Service in destroying a prevailing acetous Salt, which is apt to generate in the Vessels when the warm Air has free Access to them; and tends to pervert the Order of Fermentation, and, instead of a Wine or Wash, produce a Vinegar. Special Care must also be had, that no Remains of Yeast, or cadaverous Remains of former fermented Matters, hang about the Vessels, which would infect whatever should be afterwards put into them; and cannot, without the utmost Difficulty, be perfectly cured and sweetened.
The occasional Closeness of the Vessels may in the large way, be provided for by Covers properly adapted; and, in the small way, by Valves, placed in light Casks. These Valves will occasionally give the necessary Vent to preserve the Vessel, during the Height of the Fermentation; the Vessel otherwise remaining perfectly close, and impervious to the Air.
It is a Mistake of a very prejudicial Nature, in the Business of Fermentation, to suppose, that there is an absolute Necessity for a free Admission of the external Air. The express contrary is the Truth, and very great Advantages will be found by practising according to this Supposition. A constant Influx of the external Air, if it does not carry off some Part of the Spirit already generated, yet certainly catches up and dissipates the fine, subtile, or oleaginous and saline Particles, whereof the Spirit is made, and thus considerably lessens the Quantity. By a close Fermentation this Inconveniency is avoided; all Air, except that included in the Vessel, being excluded. The whole Secret consists in leaving a moderate Space for the Air at the Top of the Vessel, unpossessed by the Liquor. When the Liquor is once fairly at work to bung it down close, and thus suffer it to finish the Fermentation, without opening or giving it any more Vent than that afforded it by a proper Valve placed in the Cask; which, however is not of absolute Necessity, when the empty Space, or rather that possessed by the Air, is about one tenth of the Gage; the artificial Air, generated in the Operation being then seldom sufficient to open a strong Valve, or at most not to endanger the Cask.
This Method may be practised to good Advantage by those whose Business is not very large; but it requires too much Time to be used by the large Dealers, who are in a manner forced to admit the free Air, and thus sustain a considerable Loss in their Quantity of Spirit, that the Fermentation may be finished in the small Time allowed for that Purpose. It may, however, be said, that the silent, slow, and almost imperceptible vinous Fermentation, is universally the most perfect and advantageous.