Wine-Making

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Wine-Making

 

making wine from grapes by alcoholic fermentation. Wine-making is divided into an initial stage, including the processing of the grapes and the preparation of the wine materials, and a secondary stage, including the processing and aging of the wine material to give it its characteristic taste, bouquet, aroma, and stability. The initial raw material for wine-making is grapes (white, rose, black, or red) in the stage of production maturity, that is, in the condition in which adequate quantities of extractive substances, sugar, and acid for the production of the particular wine have formed. Wine materials are prepared from the grapes at initial processing wineries, which are usually located in the regions where the grapes are grown. Then the wine materials are usually processed further at secondary processing wineries. There are also mixed-type plants.

Initial stage. The basic process in the initial stage of wine-making is alcohol fermentation. A pure yeast culture (2-3 percent) is introduced into the must for that purpose. Fermentation can also occur with the natural yeasts that are contained in the grape itself. As a result of fermenting the sugar in the grape must, ethyl alcohol and carbon dioxide are formed (on the average, 1 gram of sugar produces 0.6 milliliters of alcohol), in addition to small quantities of secondary products of fermentation (glycerine, acetaldehyde, acids, acetoin, 2, 3-butanediol, diacetyl, and higher alcohols and ethers). The must is brewed until the sugar is completely fermented when dry wines are being made or until partial fermentation for semis weet, full-bodied, and dessert wines.

White table wines are made primarily from white grapes; red and black grape varieties whose juice is not colored are also used (for the so-called white method; see Figure 1).

In order to avoid souring, the grapes are immediately processed into must at the wineries. In crusher-stemmers the grapes are mashed and turned into pulp, and the stems are separated from the pulp and juice. A pulp pump feeds the pulp into a runoff unit for separation of the free-running must, and then to a continuous or periodic-action press for final pressing. The must is cleared by settling or decanting for 18-24 hours with simultaneous treatment with bentonite and sulfur dioxide. A pure yeast culture is introduced into the clarified must, which is then put into tanks or installations for continuous fermentation. For the best table wines only the free-run must is used; the press fractions of must go for making ordinary fortified wines. During fermentation the must is kept at an optimal temperature (14°-18° C). When the must is fermented in a continuous-action unit the productivity of the equipment increases 30 percent, labor input is cut 50 percent, the diluted yeast preparation is introduced once at the start of the wine-making season, the maintenance of production parameters at the optimal level is easier, and higher wine quality is ensured. When fermentation of the wine has ended—that is, when the discharge of carbonate gas has

Figure 1. Production system for preparing white table wines: (1) container with grapes, (2) bunker-feeder , (3) rolle r crusher-stemmer, (4) pulp pump, (5) sulfur doser for pulp and must, (6) discharger, (7) must receptacle, (8) pump, (9) bentonite doser, (10) must clarifier, (11) device for continuous must fermentation, (12) wine material clarifier, (13) wine storage tank, (14) final crushing press, (15) alcohol doser

stopped and the wine has cleared—the wine is poured off from the yeast sediment and pumped into a clean tank.

Red table wines are made from red or black grape varieties whose juice is ordinarily not colored; all coloring substances are contained entirely in the skin. The primary task of wine-making by the so-called red method is to extract the coloring substances (anthocyanins). After crushing and stem-removal, the grapes are not pressed as is done when making white wines. They are processed by one of three production systems. The first system consists of fermenting the must in the pulp (Figure 2) in oak vats or reinforced-concrete tanks at a temperature of 28°-32° C with a floating or submerged “cap” (the mass consisting of skin and grape seeds). Because of the action of the carbonate gas the grape

Figure 2. Production system for preparing red table wines with pulp fermentation: (1) container for grape delivery, (2) bunker-feeder, (3) centrifugal crusher-stemmer, (4) pulp pump, (5) sulfur doser for pulp, (6) tanks for pulp fermentation, (7) mixer for remixing “caps,” (8) pulp pump, (9) discharger, (10) pumps, (11) tank, (12) tank, (13) final crushing press

skins float to the top and thicken on the surface of the fermenting must in the form of a cap. The skin is carefully mixed three or four times a day for fuller extraction of its coloring and tanning substances. When the wine acquires the necessary color, it is separated from the pulp and the pulp is pressed. The second system consists of heating the pulp to 55°-60° C in pulp-heating units, keeping it at this temperature until the must acquires the desired coloring, then cooling, pressing, and fermenting by the white method. The third system includes extracting the coloring and tanning substances by means of fermented wine material (see Figure 3). In this system, the must is separated from the pulp and fermented by the white method, and then the wine material is put into an extractor for extraction of the coloring and tanning substances from the fresh pulp. Because the alcohol content in the wine is relatively high, extraction proceeds very quickly (in 8-10 hours). This procedure is carried out on a flow production line where all processes are fully mechanized and automated.

After clarification and an intensive coloring have been achieved, red table wine materials obtained by all three production systems are poured off from the yeast sediment and sent for further processing and aging.

Fortified (full-bodied and dessert) wines are made from grapes that have a capacity for high sugar accumulation during the ripening process and also for wilting and turning into raisins when overripened. The aroma and taste of these wines are conditioned by the grape variety (muscatel, Tokay) or the method of production (sherry, Malaga, Madeira, port, Marsala, Cahors, and others). The wine is processed in the same way as table wines are. After fermentation of part of the sugar at percentages defined for each type of wine, the fermentation is stopped by the introduction of pure, potable ethyl alcohol. This is the so-called fortification of the wine.

In order to obtain semisweet wines, the fermentation can be stopped by such means as sharply reducing the temperature, introducing large dosages of sulfur dioxide, and heating to 80°-90° C with multiple filtration.

Secondary stage. Underground storage areas or aboveground buildings with air conditioning are highly effective for aging and storing wine. The wines are stored in oak barrels and casks, as well as in enameled tanks.

Aging is processing for the purposes of obtaining wines of a definite type and of achieving stability. Operations such as adding, racking, clarification, filtration, fining, coupage (blending), cooling, and pasteurization are done at this time. Wine is added to make up for wine lost because of evaporation and to protect it against souring. The wine evaporates

Figure 3. Production system for preparing red table wines with extraction of coloring and tanning substances by flow process: (1) container, (2) bunker, (3) crusher, (4) pulp pump, (5) sulfur doser, (6) extractor, (7) pumps, (8) pressure tank, (9) device for continuous fermentation of must, (10) tank, (11) tank, (12) pump, (13) tank, (14) final crushing press

through the pores of the staves and groove openings of the barrels. Air cavities form in the pores and cause table wine to sour. In order to avoid this, wine of the same age, variety, and quality is regularly added. Racking is the separating of the transparent part of the wine from the residue, which includes yeasts (the first racking), adhesive sediments, and other substances. The oxidation processes that occur as a result of the wine’s contact with the oxygen in the air during racking accelerate the maturation of young wines, improve the taste, increase transparency, and develop the wine’s bouquet and aroma. The wine is clarified by filtration and fining. Under the influence of the oxidation processes, certain components of the wine—tannin, yeasts, pectin, and coloring substances—change to a suspended state, form a cloud, and then fall as sediment. Cream of tartar and micro-organisms (yeasts and bacteria) also settle. The wine is filtered through diatomite, asbestos, cellulose, cloth, and other filters. Fining involves treating the wine with various substances that adsorb the clouding particles and form settling flakes with them. In Russia, fish gum from the air bladders of sturgeon was initially used for this purpose; gelatin, casein, sodium alginate, and bentonite were subsequently used. Potassium ferrocyanide or Phytin are introduced to remove surpluses of iron from the wine.

The coupage of wine is an important means of improving its quality. This involves mixing wines from different grape varieties of different regions, different years, and different types (dry with sweet, red with white, and so on). By cou-page, it is possible to obtain large batches of uniform, standard wines, to eliminate defects and weaknesses in wines, to make them younger, and to cure sick wines. Wines are cooled at temperatures from —3° to —4° C and held for up to three days with subsequent filtration in order to remove sur-pluses of cream of tartar and yeast, pectin, and coloring substances that frequently cause cloudiness. Futhermore, cold treatment improves the quality of the wine. Usually pasteurization is used for wines that are sick or prone to sickness; it gives the wine resistance to oxidation processes and also accelerates maturation. Heating the wine to 60°-70° C and holding it there for several hours with subsequent filtration increases stability and improves the wine’s taste. Good results are obtained by aging full-bodied wines during the summer in the sun, either in open areas or in glassed-in rooms.

Wine is bottled on automated lines. The filling lines usually include a washing unit, a sorting machine for rejecting empty bottles, a sterilizer for empty bottles, a filling machine, a corking machine, a sorter for full bottles, a labeler, a wrapping machine, and a bottle-packing machine. During filling the wine should not be subject to aeration, which causes it to cloud. In the wine-making industry of the USSR a great deal of attention is devoted to introducing the latest machinery and production processes: highly productive flow lines for processing grapes, continuous fermentation units, automated filling lines, large-capacity metallic (or enameled) and reinforced-concrete containers, automatic shops with remote-control consoles for aging and processing wines, devices for thermal processing of wine, tank trucks and railroad tank cars for transporting wine, bottle pasteurizers, ultra-coolers, sulfur dosing units, alcohol dosing units, and other equipment.

REFERENCES

Gerasimov, M. A. Tekhnologiia vina, 3rd ed. Moscow, 1964.
Nilov, V. I., and I. M. Skurikhin. Khimiia vinodeliia, 2nd ed. Moscow, 1967.
Nilov, V. I., and S. T. Tiurin. Sozrevanie i khranenie vinomaterialov v krupnykh rezervuarakh. Moscow, 1967.
Valuiko, G. G. Tekhnologiia stolovykh vin. Moscow, 1969.

G. G. VALUIKO