Diversity of Opinion on Stemming.—There is no subject connected with wine making upon which there is a greater difference of opinion than that of stemming. And it would seem that the diversity of practice is not always caused by the different conditions and exigencies of location, variety of grapes, etc.; but among the different wine makers in the same locality, some remove the stems, and others do not; from which Dr. Guyot infers that the practice cannot be classed among the essential principles governing vinification, but is a mere matter of detail, and that stemming may be practiced or omitted without materially affecting the wine. But Machard, a writer of the Jura, lays it down imperiously as one of the very essentials of good wine making that the grapes should be fermented with the stems, and calls stemming a pernicious practice.

Effect of Stemming.—All agree, however, that the stems, during fermentation, if not removed, yield tannin to the wine, and thereby give it astringency. It is also said to increase fermentation, by furnishing to the must additional germs of fermentation adhering to the stems, and perhaps acting also in a mechanical way, by presenting many salient points, and exposing a greater surface to the action of the ferment.[1] They also add a certain amount of acid to the wine, if green. It is evident that they increase the labor of pressing, by adding to the mass of marc.

Proper Practice.—If, therefore, by reason of the variety of grapes cultivated, or the soil, or situation, your wine is too soft, lacks life and astringency, ferment with all or a portion of the stems; but if your wine is rough, too astringent, it will be found beneficial to stem the grapes. If your grapes lack the fermentive principle, and fermentation is slow and incomplete, leave the grapes on the stem; and in the same way the fermentation will be assisted, if the grapes are overripe.

When the grapes are fermented with the stems, care must be taken that they do not remain too long in the vat, or the wine may acquire a bitter, disagreeable flavor, called by the French goût de râpe, or stem flavor, which is caused by the bitter principle contained therein, and which is dissolved out by maceration.

To Estimate Tannin.—A certain amount of tannin is necessary to the proper clearing of the wine, which is brought about by the tannin combining with albuminous matters, and they are then precipitated, and the wine may be drawn off, leaving them at the bottom of the cask. It is on the application of this well known principle that Maumené gives a very simple method of ascertaining whether the grapes should be stemmed or not. He says: First make a small quantity of wine without the stems, and add tannin, or, what is better, a decoction made by boiling a quantity of stems, and if sensible precipitation is produced, it is better to ferment with the stems, for tannin is wanting; but if the precipitation is not formed, the grapes should be stemmed.

Stemmers.—This is usually effected in California by the use of the common hand stemmer, though some large establishments are using a stemmer run by steam or horse-power. The common stemmer consists of an oblong shallow box or frame, six or eight feet long by two wide, or any convenient size, and about six inches deep, with a coarse wire netting or grating stretched across the bottom. This grating is usually made of heavy galvanized iron wire, with ¾ inch or inch meshes. Instead of having the grating extend the whole length, a portion at one end may be floored with wood, upon which a box of grapes can be placed without injuring the grating. The only objection to this stemmer is that the grape juice comes in contact with the metal of the grating, and it is a well known fact that nearly, if not all, of the baser metals are corroded by the acids; it would be better to replace the wire with a wooden grating, as in France (Fig. 3.).

How to Remove the Stems.—The grapes are dumped from the boxes directly into the stemmer, and the workman seizes as many as he can easily manage with both hands, and rubs and rolls them to and fro upon the wire grating, and the berries, as they are rubbed off, fall through the meshes, and the stems remain in the hand. The few grapes that may remain are removed by raising the mass of stems and forcibly throwing them two or three times upon the grating. Sometimes the stems, with the few grapes clinging to them, are turned over to another workman, who, with a hay fork, tosses them about upon another grating till all the berries are removed. The stemmer ought to be situated over the hopper of the crusher, so that the grapes will fall directly into it, as they are separated from the stems.

Crushing.—It is generally considered essential to crush the grapes whether stemmed or not, although in some special cases, to be hereafter noted, crushing is omitted.

Methods of Crushing.—It is well known that in Europe the grapes are usually crushed by being trodden with the feet of men, usually barefooted, but sometimes in wooden shoes, and many of the best writers of to-day are of the opinion that the wine is better when the grapes have been well trodden with the bare feet, for by thoroughly rubbing the skins and pounding them into a pulp without breaking the seeds, they think that more color and aroma are developed than can be obtained by simply crushing them, as in a machine, and afterwards fermenting. Although the practice of treading is the more common one in Europe, yet there are exceptions, and in some places the crushing is done by rollers and with satisfactory results. In California we are accustomed to regard the treading of grapes as an antiquated practice, and a relic of a past age, and it is almost universally discarded, being practiced only occasionally and by Europeans, who have not yet wholly fallen into our methods of practice. Those who are fastidious in this matter may rest assured, that if they will drink California wine, they run but very small risk of imbibing a liquid which a man has had his feet in.

Aerating the Must.—There seems to be some confusion on this subject, for some claim that the must is better exposed to the air, and prepared for fermentation, by treading. This may be true of treading in the vat during fermentation, but simply treading the grapes to crush them does not aerate the must as much as crushing with rollers, for in the latter case the juice falls through a considerable distance in a finely divided form, which thoroughly exposes it to the air.

Crushers.—The machine generally employed consists of two rollers made of wood, iron, or other suitable material, 6 or 8, or even more, inches in diameter, geared together so that they revolve in opposite directions and towards each other, and so that the grapes will be drawn between them from above. The rollers run near each other, but do not touch, so that the grapes will be crushed, and the seeds remain unbroken. It is operated by one man turning a crank, either attached to one of the rollers or to a pinion. Figure 4 represents such a crusher, except that in the figure the rollers are open-work, instead of solid, as they should be. It is surmounted by a hopper which allows the grapes to fall between the rollers as they revolve, and the whole apparatus should be so placed that the pomace may fall into the fermenting vats, or be easily conveyed to them or to the press, accordingly as it is to be made into red or white wine.

Some stemmers have corrugated instead of plain rollers, but there is no advantage in this, and unless they are very nicely adjusted to the motion of the cog wheels, they may break the seeds, which is always considered injurious to the wine.

Rapidity of Operation.—Five men—one to handle the boxes of grapes, two to stem, standing on opposite sides of the stemmer, one to operate the crusher, and one to take the stems and remove the remaining grapes and to make himself generally useful—can stem and crush with these hand machines twenty tons of grapes per day, enough to make three thousand gallons of wine. And the work can be done much more rapidly by the use of the stemmer and crusher combined, which is to some extent used in the largest establishments.

Special Practice.—Boireau says that it has been observed that of the Médoc wines, those made without crushing the grapes have less color than those made from grapes of the same crop which have been crushed, but that they have a more refined and delicate taste (plus fins de goût), and that consequently many of the proprietors of the grands crûs of the Médoc in those years which are favorable to the maturity of the grape do not crush; they only do it in inferior years, when the grapes have not become sufficiently ripe, and when they fear that the wine may not have a suitable color. And in another place he tells us that in those grand wines which are intended to be bottled, a superabundance of tannin and its consequent roughness may be avoided by complete stemming, fermenting the whole berries, and by drawing from the fermenting vat at just the right time.