Letters on the Culture of the Vine Part 8: Fermentation of the Wine

Letter XIV – Fermentation of the Must – Primary Fermentation

For convenience? sake, the process of the vinous fermentation has been divided into two stages, the first being termed the primary, violent, or tumultuous; the other, the secondary, gentle, or insensible fermentation. The former being that which is usually conducted in the vat. The latter, that which commonly takes place after the new wine has been racked from the vat into the cask. We have now to treat of the first, and of certain methods before alluded to, of abating its violence, when the wine maker has reason to apprehend that it may be such as to produce an injurious effect upon the quality of the wine.

In from one to fifty hours after the must has been expressed, the fermentation will in this climate usually have established itself. In colder countries the period is often much prolonged, here it seldom exceeds thirty-six hours. It commences by the formation of a slight scum on the surface of the must, which gradually, and by insensible degrees increases, until it becomes of considerable thickness: a circle of small bubbles then forms itself round the margin; the scum continues to thicken, until at length it cracks in various places, and bubbles of carbonic acid gas rise and burst in various parts of the surface. This is the critical moment for depriving the must of a large portion of its ferment, and by this means to prevent the fermentation from rising to that excessive degree of violence which is usual here in warm weather, particularly if the grapes have not obtained a very high degree of maturity. At this period a large proportion of the ferment is collected at the surface, and forms, in fact, the scum above-mentioned; and if it be carefully skimmed, or what is better, if the contents of the vat be racked off into another fermenting vessel, leaving this ferment with a small portion of the lees behind, it is probable that the subsequent process will proceed much more gently, and the temperature of the mass be kept much lower than otherwise would have been the case. In making experiments some years since, I ascertained this fact, and I have since been informed that the practice of racking off the must at the commencement of the fermentation, prevails in a few districts in the south of France, where it is considered desirable to prevent perfect attenuation in the fermenting vat, that the insensible fermentation in the cask may be prolonged. This is precisely the result which has attended my experiments; and although the untoward rainy weather, which, during the last two seasons interfered with our operations in wine making, by rotting the grapes, and compelling us to hasten the gathering of the crop, prevented my carrying on these experiments in the manner, and to the extent I desired, I have no doubt as to the accuracy of my observations, and the soundness of the principle. By subjecting equal portions of the same must to fermentation, I ascertained, that when it had not been racked off from its ferment, the temperature rose from 12 degrees to 15 degrees higher than it did in those portions in which the separation had been made. I recommend this fact to the attention of those wine makers whose produce is liable to suffer from the excessive violence of the first fermentation. If they desire to avail themselves of it, they should have the process watched narrowly, and seize the moment when the scum begins to crack, and the bubbles of gas to burst in various parts of the surface; if the racking be delayed ten or fifteen minutes longer, the increasing agitation of the liquor will have re-combined a portion of the ferment, and the same result be no longer obtainable. When the grapes have become exceedingly ripe, and the weather at the gathering is cool and temperate, I do not consider it expedient thus to deprive the must of a portion of its ferment, particularly if the fermenting mass be not of considerable volume. If, however, the wine maker desires to make a sweet wine, he will find his object much more easily attainable by the adoption of the means just described.

From the stage above-mentioned, the fermentation rapidly passes into the tumultuous, and, if means have not been used to check it, the temperature rises, sometimes to the extent of 96 degrees to 98 degrees; a dense head of froth of several inches, and sometimes (if the volume of the fermenting mass be considerable) of several feet in thickness, covers the vat, whilst a rapid internal motion, caused by the escape of small bubbles of gas, pervades the entire mass, which has now become greatly increased in volume. Large quantities of carbonic acid gas are now detached from the surface, which being vastly heavier than the common air, flows over the sides of the vat, and, unless means have been taken for its dilution with the latter, by a free current, speedily fills the apartment; the lower levels being, of course, first occupied. No person should venture, without a light, into a closed building in which there are considerable quantities of fermenting wine; for unless freely ventilated from the bottom, there is danger of instant suffocation. Wherever the candle will not burn brightly there is danger; and it should be understood, that owing to the weight of the gas, the danger is always greatest at the lowest level. I have known a cellar situated underneath the place where the wine was fermenting, and communicating with it, by a large trap door, so filled with this dangerous gas, as to be unsafe to enter until it was expelled. After a period, longer or shorter, according to the violence of the fermentation, and the quantity of sugar contained in the must, it begins to abate. With me, this period usually varies from thirty-six to seventy or eighty hours. The sweetness of the must has now probably almost disappeared, and more or less gradually, the mass subsides to nearly its original bulk. As soon as this is observed, it should be watched, because it is desirable to rack it into casks before the sweetness has altogether disappeared, or, at all events before the wine has become perfectly still. The exact period for racking off from the vat, there are in different countries various rules for determining, but here we may safely reduce them to two. First, the disappearance of sweetness; whenever this takes place, although there may be, and indeed, almost invariably, is, sugar remaining in the wine undecomposed, but masked by the harsh roughness of the latter, there can be no more than is absolutely requisite to feed the secondary fermentation in the cask. Secondly, when the fermentation subsides so as to become comparatively gentle, it may still be quite sweet to the taste, and have a considerable quantity of its sugar undecomposed, nevertheless, it cannot gain by remaining in the vat. Whenever, therefore, the fermenting mass attains either of these two conditions, it should immediately be drawn off into casks. As this brings us to the termination of the first or violent fermentation, with reference to white wine, we may now retrace our steps to describe what modifications of the process are requisite in the manufacture of red wine.

To make this, as we have seen before, it is necessary that the skins or marc should be fermented with the must, to extract the color, and the peculiar astringent principle which accompanies it. In France, when quality is an object, it is a general, although not an universal, practice, to separate the berries from the stalks, on account of the bitterness imparted by the latter to the wine. Of various methods for performing this, the most approved seems to be, to rub the bunches of fruit over a coarse wire grating enclosed in a frame, under which is placed a large vessel to catch the berries, which fall through as they are detached; the stalks, as they are rubbed bare, being collected and thrown on one side. I prefer, however, to crush the grapes in the usual way first, and to submit the marc to the action of the screw, to render it dry enough to handle. Then to spread it thinly upon any clean surface; a floor or cloth for instance, and with a light wooden rake, having fine teeth, set very close together, to rake out the stalks. This method gives very little trouble. I then prefer to keep the skins thinly spread out, and sometimes turned to prevent them from heating, until the fermentation is about to commence in the vat, and the must is drawn off from its yest as above described; then to add them to the former. Sufficient allowance should, of course, have been made in filling the vat for the space they occupy. Another method is also taken when we do not consider it advisable to deprive the must of a portion of its ferment, and are thus enabled to add the skins to it, without waiting for the commencement of the fermentation; and this is, as soon as a quantity of the grapes has been sufficiently crushed in the treading box, to pass their skins through a common riddle, with meshes an inch square, which separates them from the stalks sufficiently, and is performed without difficulty. As soon as the fermentation is fairly established in the vat, the whole mass of the marc is thrown up to the surface in the form of a thick crust, or head, the under portion of which is alone subjected to the action of the fermenting must, so as to give out the whole of its color. To remedy this it is usual, where a high colour is considered essential, to beat down the head of the marc frequently, that it may be all acted upon. Still the action upon the marc remains incomplete, because it is again immediately thrown up to the surface; besides which, another evil is sometimes brought about by this practice. The surface of the marc has a tendency to run rapidly into the acetous stage of fermentation, and may become, quite acid in a few hours. If this be now beaten down through the fermenting mass, an acid impregnation will be communicated to the whole, and the wine be more or less injured. To obviate both difficulties, a simple and ingenious plan has been devised, which appears well to merit adoption in the manufacture of red wine. The object is to keep the whole body of the marc some inches beneath the surface of the wine; and to effect this, a sort of false lid is fitted to the inside of the vat, about 14 or 15 inches from its upper margin. This lid is composed of loose boards, but made so as to fit closely together. After the marc is put into the vat, a sufficient quantity of the liquid is drawn off from the bottom, to lower the upper surface to the part to which the lid has been fitted. The boards of which it is composed, are then laid on this surface; and to prevent them from rising when the wine which was drawn off from the bottom is returned to the vat, three cross pieces are laid upon them, at equal distances from each other, and crossing the lid at right angles. These cross pieces are confined to their places by having each end slipped under a chock of wood, previously nailed securely to the inside of the vat, at the required height from the top. The lid being now securely fixed, the wine drawn off is returned to the vat, and, of course, covers the marc and the lid to the depth of several inches. The fermentation of the red wine having proceeded until the moment for racking it into casks has arrived, it will be more convenient that I should defer to another paper the description of this part of the process, which is similar to that adopted with white wine; except in one particular, viz., the disposal of that portion of the wine which is contained in the marc: I shall, therefore, conclude this paper with some account of the latter.

We will suppose the wine to have been drawn out of the vat down to the lees, the marc is then usually taken out in tubs and carried to the press, and then expressed much in the same manner as I have described in a former paper, in treating of the skins of white grapes. In the various wine districts, there are different modes of disposing of the wine so obtained; sometimes it is equally divided through the casks of wine drawn off from the vat, to impart a higher color, and more body and astringency; and sometimes it is kept quite separate, as inferior in quality. As a general rule, it is added to those wines which are chiefly valued for their strength and full body, and is excluded from those which are prized for their lightness and delicacy of flavour. The wine maker here, must, therefore, decide for himself, according to the nature of his wine, and the object he has in view. He may be assured that the addition of the wine expressed from the marc, will communicate a degree of harshness and astringency, which his vintage would not otherwise have possessed, but these qualities are greatly modified by age, and generally so much mellowed by long keeping in the cask, that the wine which has received it, often finishes by becoming the best.

Letter XV – Secondary Fermentation

In the preceding paper we brought to a close an account of the primary or tumultuous fermentation, and we left the subject at that point when the wine was considered to be in a fit condition to rack into casks. The processes to be adopted in preparing these for use have already been described, we will, therefore, suppose that the wine maker is well provided with a sufficient number of various sizes, all in fit condition, and with properly fitted bungs. It is not requisite, and perhaps not advisable, that the casks should, in the first instance, be mounted up on their proper stands in the cellar they are ultimately to be placed in, on account of the increased temperature, greater or less, according to its state, the still gently fermenting wine cannot fail to impart to any cool cellar. If the fermenting cellar be secure, and not too much exposed to currents of air from without, it will be better to keep the freshly filled casks there, in such manner that free access may be had to each, to fill it up frequently. In racking from the vat into the casks upon the ground, the most convenient plan is by a tube, driven into the hole left within three or four inches of the bottom of the cask or vat, which, for this purpose ought to be one inch and a-half in diameter. This tube is usually made of any tough close-grained wood, and has attached to it a hose of well-seasoned leather, of suitable length, with another tube attached to its extremity to drive into another cask, or as in this case, to be inserted into the bung-hole. A little care in the use of this simple instrument, enables two, or at most three men, to rack off a large quantity of wine in a short time, without the least waste or loss of the aroma and spirit of the wine, which must occur in drawing it off into buckets or tubs, and pouring it through a funnel into the casks. In the absence of the tubes and hose above mentioned, the wine may be drawn off into buckets, and poured into the casks through a large funnel. Previously to their being filled, the casks, which I will suppose to be ranged on the ground, as near as possible to the vat from which they are to be filled, and securely checked, will require to undergo the following preparation. Let a quantity of the wine to be drawn off, be heated to the boiling point, in any clean convenient sized vessel, and the scum being first removed, let about a quart be poured quite boiling into each cask. Put the bung in tight, and have the cask well agitated from end to end, turning it gradually round, until every part has been brought into contact with the boiling wine. Then take the bung out, and drain off the wine into a tub or bucket, and return the cask to its former position. There are two objects in this; first, to prove if the cask be quite staunch; if it have any faulty place, the hot liquid will be sure to discover it, as every cooper knows, for this purpose boiling water would have answered equally well; wine, however, is used because it is desirable to saturate the inside of the cask with the same liquid with which it is to be filled, and by using it hot to drive out any water which may have remained since the cask was cleansed, and which may, and very often does, when left in, communicate an unpleasant flavour to the wine. In France, they sometimes use about a pint of good brandy for the same purpose, but that interferes with sulphuring the cask, as I shall shortly point out. The hot wine having been drained off for a few minutes, and the cask returned into its position, take about three to six square inches of sulphur match (made by dipping into melted brimstone strips of linen or calico rag, and of which a sufficient stock should always be ready for use in every wine maker’s cellar,) and having suspended it upon a piece of crooked wire about a foot long, light the end of the match, and insert it into the hung-hole; then immediately put in the bung, and hold it forcibly down, while the match is burning. The sulphurous acid gas generated by the burning sulphur, drives out, with a loud hissing noise, the atmospheric air, of which it takes the place. If the wine be now added to the cask, it becomes more or less impregnated with the vapour of the burning sulphur, which is said to cause the precipitation of the ferment still suspended in large quantities in it, and thus to hasten the period when it can be racked off from the lees. But, whatever may be its mode of action, the burning of the sulphur in the casks certainly operates as a great antiferment, and checks effectually, if used with judgment, the tendency to the acetous degeneration, as well as too violent a fermentation in the cask. It is sometimes the practice to grate down spices and aromatic herbs into the melted sulphur, but I believe the simple match answers every good purpose; and I have never discovered the odour of the sulphur to remain, at all events, after a few weeks. Observe, that no brandy cask, or cask recently rinsed with brandy, should be prepared by burning a match in it. The probability is, that if any of the spirit remain in the cask, which in the former it is almost sure to do, the head of the cask would be blown out, sometimes with great force, and a loud explosion. I have known the accident, through carelessness, to happen repeatedly. The casks being now properly prepared, may be filled with new wine. If the quantity be considerable, several small casks of gradually diminishing capacity should be filled, that a supply for keeping the others constantly full may be always at hand, without touching the contents of one of the larger. It is not advisable, in most cases, to mingle the thick wine, which remains at the bottom of the vat, with the remainder of its contents; it is best to keep it apart.

After it is drawn off from the vat, if the proper period has been taken, the wine begins to ferment gently in the casks, and in so doing, usually throws off a considerable quantity of froth, together with such skins, seeds, &c., as may be floating in it. The escape of these, as well as of such portion of the yest as may be thrown up to the surface, should be promoted by keeping the casks constantly full. To accomplish this, they will at first require to be replenished, at least three or four times during the twenty-four hours, diminishing gradually to once a day, three times a week, and so on, until they can finally be bunged up close. If during the process of filling up the casks, the seeds or skins should be observed to be in such quantity that the fermentation is insufficient to cast them forth, they should be removed by hand. This gentle effervescence is termed, as we have already seen, the secondary fermentation, and the longer it is sustained, in a perceptible degree, the more rapidly will the new wine meliorate itself, and the more generous will it become. All the experience I have had in the manufacture of wine in this colony, has tended to confirm me in the opinion, that a tumultuous fermentation, not over violent, and of not less than sixty to eighty hours duration, followed by a distinctly perceptible secondary fermentation of several weeks, (provided the grapes have been rich in the saccharine principle, and without which condition, it could scarcely be so prolonged,) is the modification of the process, which in our climate it is desirable to attain, in order to elaborate fully the qualities of the wine. If the first fermentation be over violent, and the fermenting mass considerable, it is probable that so much of the sugar will be decomposed during this part of the process, as greatly to abbreviate the duration of the secondary fermentation, for want of sugar to feed it; and in this case I have usually found the wine, for a length of time, difficult to fine and get into good order for use. Such wine, though occasionally of considerable strength, has usually been characterised by greater harshness and bitterness, by inferior fragrance, and a want of that mellow flavour which is found in all really good wine. I should always prefer to have the sugar still distinctly perceptible to the taste, in fact, to have the wine sweet when it is racked from the vat, and even to continue so, in a slight degree, at the expiration of several weeks. The necessity of keeping casks of new wine constantly full, is one of the conditions which it is necessary to observe most rigorously in its management; and I shall now proceed to explain the reasons.

The wine fresh from the vat, still contains a large portion of its ferment, in an unaltered state, a very small proportion (as we have before seen) being decomposed by the vinous fermentation. A portion of this ferment, the secondary fermentation has a tendency to throw up to the surface, in the form of a head of froth, from whence, if the cask be quite full, it escapes by the hung-hole. If the wine be allowed gradually to subside in the cask through neglect, this outlet for it is prevented, and it in part attaches itself to the inside of the staves round the bung, these having been first saturated with wine, now become coated with that very principle, which, as soon as all the sugar in a fermented liquor has been decomposed by the vinous fermentation, becomes the active agent in exciting the acetous stage, and converts it into vinegar. Now the new wine contains a considerable quantity of fixed air, which as it disengages itself through the bung hole, causes the former to diminish rapidly in volume, hence one reason that, to keep them full, casks of new wine require to be so frequently replenished; but, another cause is the high temperature acquired during the violent fermentation, and the consequent reduction of its volume as it cools down in the cask. If the operation be neglected for a few days, sometimes even for a day, the wine will have shrunk several inches, leaving a large portion of the inner surface of the staves exposed to the action of the atmosphere; the effect of which will almost infallibly be, to convert into vinegar, by means of the ferment with which they are coated, the wine they have previously absorbed. Persons who have never witnessed it, would find it difficult to credit how rapidly this conversion sometimes takes place. If the cask, after being for a longer or shorter period neglected, be now filled up, an acid impregnation, more or less according to the extent of this neglect, is imparted to the whole contents of the cask. It may not at first be perceptible to the taste, and the wine, if generous, may be enabled to resist the leavening of vinegar it has received, in which case it will continue sound, but with the flavour produced by mixing a small quantity of vinegar with a considerable body of wine. But the chief danger consists in this, that the acetic acid or vinegar, being once introduced into the wine, remains unchanged; unless destroyed by some alkaline preparation, it cannot be reconverted into wine, and its natural tendency is to exert its agency upon the rest of the wine, sometimes by a slow and almost imperceptible process, until it converts it into vinegar also. I am persuaded that more wine has been spoilt amongst us by neglecting to keep the casks constantly full, than by all the other causes of failure put together. To guard against this evil, therefore, as soon as the wine has been racked off, let a portion be at hand, contained in bottles and other small vessels, to keep the casks full, to over?owing. If much froth be discharged from the bung-hole, it may at first be left altogether uncovered; but, as soon as practicable, a bung upside down, should be laid over the opening. As the effervescence abates, the bung may be put into its place, and at length, when the wine has become quite still, be gradually tightened. Care, however, should be taken not to do this too soon, lest the cask should be burst by the pressure of the disengaged gas. If, as is usual, a cloth is placed under the hung, to make it fit closely, until the latter is finally driven home, the cloth should be frequently changed, or washed in lime-water. At first, it may become quite acid in twenty-four hours. All vessels of wood, which are used to contain wine, but particularly closed vessels, such as casks and kegs, should be rinsed carefully, as soon as they are emptied, with hot water, and then drained till dry. By causing this to be observed strictly as a rule, the wine grower may be assured he will prevent much wine from being spoiled.

After the wine has been in the cask a few days, it will probably have become sufficiently still to remove into the cellar, there to finish the process of the secondary fermentation.  For this purpose, the bungs may be temporarily tightened, to be loosened again as soon as the casks are mounted upon their supports, in the cellar. The supports ought to be as solid as possible, to prevent unnecessary vibration, and sufficiently high from the floor of the cellar (say from 11 to 12 inches,) to admit a common pail under the lower chimes; logs of wood, placed parallel to each other, about 12 or 15 inches apart, and squared to the breadth of 5 or 6 inches on their upper surfaces, are the best. The under surface need not be squared, but the log being gaged from the squared face, to the thickness of 8 or 10 inches, and marked with a chalk-line; notches should be taken out at intervals of 4 to 5 feet, down to the chalk-mark. These notches are intended to receive short pieces of 3 x 4 scantling crossing the logs at right angles, and serving as supports for them to rest upon. They are advantageous to block up the logs to an uniform level, when there are inequalities in the floor of the cellar, and to prevent the necessity of squaring the under sides of the logs. [See Sketch, Plate 3, Fig v.] Each cask should be kept ?rm in its place, without touching its neighbours, and, if practicable, with room between it and the wall, to admit a man to pass freely behind it, by four chocks of wood. These chocks should be about 6 inches long, and 3 ½ to 4 inches thick at the back, broad enough to ?ll up the space between the hoops, [See Sketch, Plate 3, Figs vi. and vii. This figure can be seen in Part 9] and hewn in such manner as to fit the curvature or bulge of the casks. The casks of new wine having been firmly secured as above described, a bung, of peculiar form, will now be advantageous to use, provided that there is no longer any very sensible effervescence. These bungs are made about six inches long, and taper, so that about one-half may be immersed in the wine, and the other project above the staves outside. They are serviceable in preventing so much waste by evaporation, as usually takes place when the common hung is used, especially when not driven tight, and they are much more easily taken out, without disturbing the wine, when the casks are to be filled up. Even when driven in hard, they are readily loosened by a few slight taps on the sides with the “bung starter,” or a wooden mallet. They may be made of any close grained wood, but either by boiling, for several hours, or long immersion in cold water, should be freed from any astringent gum, &c., they may contain, before they are used.