VITICULTURE.

New Zealand Journal of Agriculture, Volume XX, Issue 3, 20 March 1920, Page 187

VITICULTURE.

S. F. ANDERSON,

Vine and Wine Instructor

WINEMAKING OPERATIONS. Last months’ notes dealt principally with the time of gathering and the condition the winemaking grapes should be in when commencing the vintage. It will be assumed that everything is now in readiness in the press-house and cellar for getting in the grapes. The making of dry red wine will first be dealt with, as in New Zealand it covers the principal work, the making of sweet wine being usually an aftermanipulation by the addition of spirits and sugar to the dry wine.

Fermenting.

Where the grapes have been gathered at their maximum condition and all objectionable or green bunches thrown out, so that the resulting must comes up to the sample. obtained from the tests made beforehand and obtained from an average of the crop selected for that purpose, it can be estimated, what the probable alcoholic content of such a wine will be. Under usual conditions fermentation lasts from forty-eight to seventy-two hours. During this period, and where the grapes are fermented on their skins, the vigneron must give it close attention. The labour employed must be so divided that a reliable man is always on duty. As long as violent fermentation- is proceeding the carbonic gas given off is . a protection from the surrounding air and its contaminations. The fermentation brings to the top a thick layer of skins varying from 4 in., to 8 in. From time to time this has to be broken up and pushed down into the body of the vat. This is necessary to allow all the colouring-matter in the skins to be extracted by the process of fermentation. It is also a help in keeping the temperature down. The temperature of the fermenting mass in the vats is an important matter, and should be under control. It may vary during the day from 75 0 to 95 0 F., and between these two points (say, 85° is as high as it should go. The fermentation is prolonged by the lower and hastened by a higher temperature. If maintained as near as possible to the mean of these points the wine will be the better for it. The weather during March and the early part of April is rarely too cold to seriously check fermentation. To prevent it going too high has generally been the concern of the New Zealand winemaker. One of the effects on the wine of allowing it to work at too high a temperature is the danger of its being affected by acetic, lactic, or other harmful bacteria; while at the lower temperature vinous fermentation soon sets in and holds its own, destroying the others. To maintain a right temperature, after breaking up and pushing down the cap of skins plunge the thermometer well into the body of the vat, note its reading, and if exceeding 85" draw off some of the must and pump it over the top, repeating this till the reading shows it is within the best limits. It should be impressed on the mind of the winemaker that the grapes, fermenting-house, and all utensils teem with harmfuh bacteria. These can only be prevented from affecting the wine by keeping down the temperature, of the vat-contents, and by the greatest cleanliness in conducting the work. The floor of the fermenting-house, the grapeboxes, and utensils should all be washed at least once in twentyfour hours. The warmer ' the weather the greater is the danger. It is within the period of the grapes being put into the vat, fermentation taking place, and its removal to the cellar that the wine is made good or bad. As soon as filled the vats should be kept covered. Strong unbleached calico is the best for this purpose. The cover is removed from time to time to permit of the cap being pushed down and taking the temperature. The fermentation gradually slows down as the sugar is transformed into alcohol and carbonic gas, and the contents become cool. When completed, what was the must is now wine, and if tested with the saccharometer that instrument will float at zero

or water-level. This indicates that all the sugar has been transformed. When quite still and the wine cool it. should be drawn off, provision having been. made beforehand by a perforated shield or bunch of twigs placed over the outlet and fixed inside the vat to keep back the skins. The wine falls into a tub placed for that purpose, and. is pumped direct from that into casks. The shorter the delay in carrying out this work and the contact of the wine with the air the better for the wine. It is unavoidable in doing this that some of the thick portion goes into the casks, apart from a turbid state of the wine at this period. Before this matter finally settles in the wine a second or . silent fermentation occurs, caused probably by some unfermented portion asserting itself. To provide for the escape of the carbonic gas from this secondary fermentation place small bags of well-washed coarse sand, about 6 in. square, over the bung-holes. This permits the escape of the gas while preventing contact with the air. Some winemakers keep the wine in the vats on the skins for some days, with the object of obtaining a deeper colour. If the weather is very cool and the vat closely covered possibly no harm will result. The practice is not recommended, however. If the grapes passing through their fermentation receive regular breaking-up of the cap all the colouringmatter will be extracted by the violent ebullition they pass through.

Making White Wine.

It will be noted on reference to last month’s notes that, with the exception of Pineau Gris, the white-wine grapes do not attain the natural sugar-content of the dark ones. Wine from the white grapes is more delicate and subject to outside influences. It is not generally fermented on the skins. The white grapes are the latest in ripening and can be left to the last. The must from these grapes should not go into the ordinary wooden vats or casks in which red grapes have been fermented, as more or less colour might be imparted. There would not be any objection in the case of concrete vats, provided they were well cleaned.

The white grapes pass through the stemmer and crusher, the must coming out on to the floor of the press and running from that,into a tub. From that it is pumped into a large vat to be aerated. As the stems, and skins soon collect in the press and pile up, pressure can be applied two or three times till the press will not hold any more, after which the final pressure is completed.

Aerating the must of the white grapes is an important stage in the making of a white wine, on account of the albuminous matter in the white grapes, which is a hindrance to its keeping-qualities and fine flavour. To successfully carry out this part of white-wine-making sufficient grapes should be gathered the evening before, so that an early start can be made to fill a vat the following day, regulating the work so that the vat will be three-quarters filled early in the day. Aeration of the must for the purpose of eliminating the harmful albuminoids is done by four or five hours thorough stirring. Drawing the must off into a tub, and pumping it back into the vat, and letting it fall from a height of 3 ft. or 4 ft. is the best way of doing this. If scum collects it should be skimmed off and put into a vessel by itself, to be made use of afterwards. At the completion of the aeration pump the must

into the casks to ferment, not quite filling them, so as to allow of some working over, and cover the bung-holes with the small sand-bags already mentioned. Each day's work' should be complete in itselfstemming, crushing, filling of vat, aeration, and finally pumping into the casks to ferment. '

. As the fermentation gets strong the froth works over more or less, and vessels should be put to catch it. The sides of the casks should be wiped clean with a damp cloth several times during the day. This froth rapidly becomes sour, and would communicate with the wine if neglected, setting up acetic contamination.

Further notes on the treatment of the wines will be given next month. . ‘ 1