By menstruums is understood a body which, in a fluid or subtilised state, is capable of interposing its small parts betwixt the small parts of other bodies. This act so obviously relates to the art of brewing, especially where the extracting of the malt and the boiling of the hops are concerned, that it should not be passed unheeded by.
The doctrine of menstruums, as laid down by Boerhaave, seems most intelligible and applicable to our purpose. He says, the solutions of bodies in general are the effect only of attraction and repulsion, between the particles of the menstruums and those of the body dissolved, the whole action depending on the relation between these two; of consequence, there cannot be any body, natural or artificial, which, without distinction, will dissolve all bodies whatsoever; nor is the cause assignable why certain menstruums dissolve certain bodies: the effects of alcaline, acid, neutral, fixed, or volatile salts, any more than those of oils, water, alcohol, fire, or air, are not to be accounted for by any general rule, that universally holds true; nor even, in many cases, doth the dissolution of a body depend on the purity or simplicity of the menstruum: the nearest path then to success, is cautiously to apply every menstruum we know of to the body whose solvent we want to discover.
The elements of fire and air greatly promote the action and effect of menstruums, and in this light they are admitted as such. Water dissolves most salts, all the natural sapos of plants, and the ripe juices of fruits; for in these, the oils, salts, and spirit of the vegetables, are accurately mixed and concreted together, and malts, having the same constituent parts with them, this element becomes a proper menstruum to extract this grain: though malts, by being dried with heats which greatly exceed what is necessary to bring barley to a state of maturity, do, from hence, require greater, though determinate heats, yet inferior to that at which water boils; but such heats must be applied in proportion to their dryness, to extract their necessary parts. Even earths, by the intervention of acids, dissolve in water; but having treated of the four elements already, as far as we conceived was requisite for the art of brewing, we shall, in this chapter, confine ourselves to oils and salts, and view these acting as menstruums only.
To the definition already given of oils, it may be necessary to add, in general, they contain some water, and a volatile acid salt; that they receive different appellations, and have different properties in proportion to their respective spissitudes. Oils from vegetables are obtained by expression, infusion, and distillation; in either of which methods, a too great heat is to be avoided, as this gives them a prejudicial rancidness, and where water does not interpose, alters their color until thereby they are turned black.
In general oils unite with themselves, but, excepting alcohol, not with water, unless when combined with salts, for salts attract water, and so they do oils: hence arises many elegant preparations both natural and artificial, from which wines are formed.
The power of oils in dissolving bodies is in a proportion to their heat, and being capable, when pure, of receiving a quantity of fire equal to 600 degrees, it is not surprising this liquid should mix with gums and with resinous bodies; but the color of these, and of every subject when thrown into boiling oils, changes in proportion to the impression made on them by heat, either to a yellow, a red, or a black. Oils which are inspissated, or thickened by heat, are termed balsams. Do not the oils of malt, from the heat they have undergone, resemble these? and from the circumstance of their having endured a heat superior to that necessary for putrefaction, may they not be suspected to possess a volatile alcaline salt? Beyond doubt, the extracts from malt (though they boil at a heat of 218 degrees only) yet do they, in great measure, dissolve hops, which are gum resinous.
Salt may well be denominated a menstruum, as it is easily diluted with water; fixed alcaline salts we have already seen appear to be the produce of fire alone.—Such are never distinguished in the composition of vegetables in their natural state; though a volatile alcalious salt (the effect of heat equal or superior to that necessary for putrefaction) is found in many, and especially in such as are putrified.
The power of a fixed alcali as a solvent is great, applied (says Boerhaave) to animal, vegetable, or fossil concretions, so far as they are oils, balsams, gummy, resinous, or of gummy resinous nature, and therefore concreted from oily substances: these, this salt intimately opens, attenuates, and resolves: disposing them to be perfectly miscible with water: oils of alcohol leaving however the impression of taste naturally belonging to this salt.
Vegetable acid salt dissolves animal, vegetable, fossil, and metalline substances, except mercury, silver, and gold. In most terrestrial vegetables this salt is evident; ripe mealy corn has the least indication of it, yet extracts therefrom, when fermented, and sometimes before they are fermented, discover sensibly their acidity. Sea-plants in general have not their roots inserted in the earth at the bottom of the sea, and these in distillation yield an oily volatile alcali; but more subtil than the native acids of vegetables, are the vinous acids produced by fermentation; they dissolve equally most matters put into them, and render the whole homogene. Into a must or wort, when under this act, by means of an elæosaccharum, might be introduced the choicest flavors, and the aromatics of the Indies be applied to heighten the taste and flavor of our barley wines. The laws of England at present subsisting are indeed opposite to any improvement of this sort, from the apprehensions of abuse: but where elegance alone is intended, undoubtedly the merit of our beers and ales might thereby be increased. As such, this is a part of chymical knowledge well worth the enquiry and attention of the brewer.
Neutral salts have already been mentioned; these are very various, and very different when acting as menstruums. Resins and gum-resins are generally said to be most effectually dissolved by alcohol; but Boerhaave informs us, that sal-amoniac (a very salutary subject and a neutral salt) if boiled with gums, resins, or the gum-resins of vegetables, intimately resolves, and disposes them to be conveniently mixed in aqueous and fermenting spiritous menstruums. Of this class of salts thus much is sufficient. This observation perhaps is of too much consequence to escape the notice of the artist.