Conversations on Chemistry Part 90

There are likewise several circ.u.mstances required to produce fermentation. Water and a certain degree of heat are both essential to this process, in order to separate the particles, and thus weaken their force of cohesion, that the new chemical affinities may be brought into action.

CAROLINE.

In frozen climates, then, how can the spontaneous decomposition of vegetables take place?

MRS. B.

It certainly cannot; and, accordingly, we find scarcely any vestiges of vegetation where a constant frost prevails.

CAROLINE.

One would imagine that, on the contrary, such spots would be covered with vegetables; for, since they cannot be decomposed, their number must always increase.

MRS. B.

But, my dear, heat and water are quite as essential to the formation of vegetables, as they are to their decomposition. Besides, it is from the dead vegetables, reduced to their elementary principles, that the rising generation is supplied with sustenance. No young plant, therefore, can grow unless its predecessors contribute both to its formation and support; and these not only furnish the seed from which the new plant springs, but likewise the food by which it is nourished.

CAROLINE.

Under the torrid zone, therefore, where water is never frozen, and the heat is very great, both the processes of vegetation and of fermentation must, I suppose, be extremely rapid?

MRS. B.

Not so much as you imagine: for in such climates great part of the water which it requires for these processes is in an aeriform state, which is scarcely more conducive either to the growth or formation of vegetables than that of ice. In those lat.i.tudes, therefore, it is only in low damp situations, sheltered by woods from the sun's rays, that the smaller tribes of vegetables can grow and thrive during the dry season, as dead vegetables seldom retain water enough to produce fermentation, but are, on the contrary, soon dried up by the heat of the sun, which enables them to resist that process; so that it is not till the fall of the autumnal rains (which are very violent in such climates), that spontaneous fermentation can take place.

The several fermentations derive their names from their princ.i.p.al products. The first is called the _saccharine fermentation_, because its product is _sugar_.

CAROLINE.

But sugar, you have told us, is found in all vegetables; it cannot, therefore, be the product of their decomposition.

MRS. B.

It is true that this fermentation is not confined to the decomposition of vegetables, as it continually takes place during their life; and, indeed, this circ.u.mstance has, till lately, prevented it from being considered as one of the fermentations. But the process appears so a.n.a.logous to the other fermentations, and the formation of sugar, whether in living or dead vegetable matter is so evidently a new compound, proceeding from the destruction of the previous order of combinations, and essential to the subsequent fermentations, that it is now, I believe, generally esteemed the first step, or necessary preliminary, to decomposition, if not an actual commencement of that process.

CAROLINE.

I recollect your hinting to us that sugar was supposed not to be secreted from the sap, in the same manner as mucilage, fecula, oil, and the other ingredients of vegetables.

MRS. B.

It is rather from these materials, than from the sap itself, that sugar is formed; and it is developed at particular periods, as you may observe in fruits, which become sweet in ripening, sometimes even after they have been gathered. Life, therefore, is not essential to the formation of sugar, whilst on the contrary, mucilage, fecula, and the other vegetable materials that are secreted from the sap by appropriate organs, whose powers immediately depend on the vital principle, cannot be produced but during the existence of that principle.

EMILY.

The ripening of fruits is, then, their first step to destruction, as well as their last towards perfection?

MRS. B.

Exactly. --A process a.n.a.logous to the saccharine fermentation takes place also during the cooking of certain vegetables. This is the case with parsnips, carrots, potatoes, &c. in which sweetness is developed by heat and moisture; and we know that if we carried the process a little farther, a more complete decomposition would ensue. The same process takes place also in seeds previous to their sprouting.

CAROLINE.

How do you reconcile this to your theory, Mrs. B.? Can you suppose that a decomposition is the necessary precursor of life?

MRS. B.

That is indeed the case. The materials of the seed must be decomposed, and the seed disorganized, before a plant can sprout from it. Seeds, besides the embrio plant, contain (as we have already observed) fecula, oil, and a little mucilage. These substances are destined for the nourishment of the future plant; but they undergo some change before they can be fit for this function. The seeds, when buried in the earth, with a certain degree of moisture and of temperature, absorb water, which dilates them, separates their particles, and introduces a new order of attractions, of which sugar is the product. The substance of the seed is thus softened, sweetened, and converted into a sort of white milky pulp, fit for the nourishment of the embrio plant.

The saccharine fermentation of seeds is artificially produced, for the purpose of making _malt_, by the following process:-- A quant.i.ty of barley is first soaked in water for two or three days: the water being afterwards drained off, the grain heats spontaneously, swells, bursts, sweetens, shows a disposition to germinate, and actually sprouts to the length of an inch, when the process is stopped by putting it into a kiln, where it is well dried at a gentle heat. In this state it is crisp and friable, and const.i.tutes the substance called _malt_, which is the princ.i.p.al ingredient of beer.

EMILY.

But I hope you will tell us how malt is made into beer?

MRS. B.

Certainly; but I must first explain to you the nature of the second fermentation, which is essential to that operation. This is called the _vinous fermentation_, because its product is _wine_.

EMILY.

How very different the decomposition of vegetables is from what I had imagined! The products of their disorganisation appear almost superior to those which they yield during their state of life and perfection.

MRS. B.

And do you not, at the same time, admire the beautiful economy of Nature, which, whether she creates, or whether she destroys, directs all her operations to some useful and benevolent purpose? --It appears that the saccharine fermentation is extremely favourable, if not absolutely essential, as a previous step, to the vinous fermentation; so that if sugar be not developed during the life of the plant, the saccharine fermentation must be artificially produced before the vinous fermentation can take place. This is the case with barley, which does not yield any sugar until it is made into malt; and it is in that state only that it is susceptible of undergoing the vinous fermentation by which it is converted into beer.

CAROLINE.

But if the product of the vinous fermentation is always wine, beer cannot have undergone that process, for beer is certainly not wine.

MRS. B.

Chemically speaking, beer may be considered as the wine of grain. For it is the product of the fermentation of malt, just as wine is that of the fermentation of grapes, or other fruits.

The consequence of the vinous fermentation is the decomposition of the saccharine matter, and the formation of a spirituous liquor from the const.i.tuents of the sugar. But, in order to promote this fermentation, not only water and a certain degree of heat are necessary, but also some other vegetable ingredients, besides the sugar, as fecula, mucilage, acids, salts, extractive matter, &c. all of which seem to contribute to this process; and give to the liquor its peculiar taste.

EMILY.

It is, perhaps, for this reason that wine is not obtained from the fermentation of pure sugar; but that fruits are chosen for that purpose, as they contain not only sugar, but likewise the other vegetable ingredients which promote the vinous fermentation, and give the peculiar flavour.

MRS. B.

Certainly. And you must observe also, that the relative quant.i.ty of sugar is not the only circ.u.mstance to be considered in the choice of vegetable juices for the formation of wine; otherwise the sugar-cane would be best adapted for that purpose. It is rather the manner and proportion in which the sugar is mixed with other vegetable ingredients that influences the production and qualities of wine. And it is found that the juice of the grape not only yields the most considerable proportion of wine, but that it likewise affords it of the most grateful flavour.

EMILY.

I have seen a vintage in Switzerland, and I do not recollect that heat was applied, or water added, to produce the fermentation of the grapes.