Various materials are added to wine during the winemaking process to solve specific wine problems. For example, bentonite is added to white and blush wines to remove protein because excess protein can cause hazes to form after the wine is bottled. Small amounts of sulfur dioxide are added when grapes are crushed, and small sulfur dioxide additions continue to be made until the wine is bottled. The sulfur dioxide helps control the growth of microorganisms, and it reduces the effects of oxidation. Wines fermented from apples and stone fruits often contain excessive amounts of pectin. The pectin makes the wine difficult to clarify, so winemakers add enzymes to break down the pectin. The characteristics and use of a few common winemaking materials are briefly discussed here.
Acid blends contain roughly equal parts of tartaric, malic and citric acids. Acid blend is added to juice or wine to increase acidity. However, large quantities of citric acid are undesirable during fermentation. In addition, citric acid can give some wines an odd taste, so this material should be used with some caution. Acid blend is often used in non grape wines.
Bentonite is a fine, clay-like material. It has a negative electrical charge, and it is used to remove positively charged particles from wine. Bentonite is most commonly used to remove excess protein from both white and blush wines. It is also used to clarify white and blush wines, and sometimes bentonite is effective in clearing hazy fruit wines. A normal dose is 1 to 2 grams of dry bentonite per gallon of wine. However, it is often used at dose levels ranging from « to 4 grams per gallon. Bentonite can strip desirable aromas from wine when used in excessive amounts (more than 2 grams per gallon), so testing should always be done.
Bentonite must be mixed with water and allowed to stand for twenty-four hours before being adding to the wine. Put the required amount of hot water in the blender, turn the blender on, and slowly add the dry powder. After the mixture is cool, place it in a refrigerator and allow the bentonite to hydrate for at least 24 hours. Add the mixture to the wine slowly and stir continuously.
Citric acid is used for several purposes in home wineries. Citric acid is mixed with sulfite powder and water and used to sterilize winery pumps, hoses, filters and other winery equipment. Sulfur dioxide solutions are also used for wet barrel storage. Weak (1 percent) citric acid solutions are used to remove the "paper" taste from new filter pads, and stronger solutions (5 percent) are used to sanitize bottling equipment. Sometimes, citric acid is added to finished wines to increase acidity and improve acid balance. In small quantities, it provides a fresh, citric characteristic often appreciated in white table wines. Nevertheless, trials should always be done before making any large additions of citric acid. Significant additions of citric acid are seldom made to red wines because the citric taste may not seem appropriate.
Diammonium Phosphate (DAP)
Diammonium phosphate is a major ingredient in many proprietary yeast foods. It is added to juice or must before fermentation to supply extra nitrogen. The additional nitrogen encourages rapid yeast growth and more dependable fermentations. California Chardonnay grapes are often deficient in nitrogen, and many winemakers add DAP to all Chardonnay juices to help the yeast complete fermentation. Juices lacking adequate nitrogen can cause yeasts to produce excessive quantities of hydrogen sulfide (rotten egg smell).
Gelatin is a popular protein fining material, and gelatins are often used to reduce the bitterness and astringency of red wines. Gelatin removes a quantity of tannin roughly equal to its own weight. Sometimes, white wines have a slightly bitter finish, and sometimes the bitterness can be reduced by fining with a very small quantity of gelatin. Gelatins are also used to clarify white and blush wines. Home winemakers can purchase gelatin for fining red wines at the local grocery store. The grocery store product is sold as Knox's gelatin, and it comes in a box containing four, seven-gram envelopes. Read the package and be sure to buy an unflavored gelatin. The gelatin must be dissolved in water before being added to wine. The gelatin powder should be added to warm water slowly, and much stirring is needed. The mixture should stand for a few minutes, and then the solution should be stirred again until all of the lumps are dissolved. Gelatin solutions should not be boiled because the heat will denature the protein and render the gelatin less effective. The gelatin solution should be used while it is warm because it will solidify when cold. From 1/4 to 2 grams of a dry gelatin per gallon of wine are used to reduce tannins and astringency in red wines. Doses ranging from 1/8 to « grams of dry gelatin powder per gallon of wine are used to remove bitterness from white and blush wines, and from 1/16 to 1/4 grams of gelatin per gallon of wine are used to clarify white and blush wines. Gelatin solutions must be used with care because even small doses can strip wines of desirable odors and flavors. Add the warm gelatin solution to the wine very slowly, and stir the wine continuously to assure good mixing.
Pectinase (Pectic Enzyme)
Sometimes, commercial wineries use enzymes to increase the amount of free run juice when crushing white grapes. The enzymes break down the cells in the grape pulp. The juice is released, so pressing is easier after an enzyme treatment. Home winemakers use pectic enzymes to prevent pectin hazes from forming in wines made from various fruits or from wines made from grape concentrate. But, excessive quantities of enzymes can produce off-odors and bad tastes, so the manufacturer's directions should be followed carefully.
Sometimes, grapes grown in cold climates contain too much acid. Then, winemakers sometimes use potassium carbonate to reduce the acid content of juice before fermentation. It is also used occasionally to reduce the acid content of finished wines. Potassium bitartrate is formed, and unless this material is removed, the bitartrate can precipitate out of the wine after bottling. Because of this instability problem, potassium carbonates should not be used after wine has been cold stabilized. Too much carbonates can change flavors, raise pH and cause other wine problems, so acid reduction is best done before fermentation.
Potassium Metabisulfite (Sulfite)
Home winemakers use potassium metabisulfite crystals to introduce sulfur dioxide into their wines. Small quantities of sulfur dioxide are used to control wine microbes, and sulfur dioxide also reduces wine oxidation. When sulfite powder is added to wine, it produces about half its weight in sulfur dioxide (about one gram of sulfur dioxide is produced when two grams of sulfite are added to the wine). Strong sulfite solutions are used to sterilize just about everything in the home winery. One teaspoon of sulfite powder and two teaspoons of citric acid in two gallons of water makes an effective solution for sterilizing equipment. Some home winemakers also use this solution to sterilize bottles just before they are filled with wine.
Potassium Sorbate (Sorbate)
Home winemakers use potassium sorbate to stabilize wines containing residual sugar. The sorbate does not stop the yeast from fermenting the sugar, but it can prevent the yeast cells from reproducing. Consequently, sorbate is only effective when most of the active yeast cells have been removed from the wine by racking or filtering. The usual procedure for using potassium sorbate is to clarify, stabilize and age the wine. Then the wine is sweetened and the sorbate added just before bottling time. POTASSIUM SORBATE WILL NOT STOP AN ACTIVE FERMENTATION. The normal dose level is 200 to 250 milligrams of potassium sorbate for each liter of wine (about one gram of sorbate per gallon of wine). If too little sorbate is added, the wine may start to ferment. If too much sorbate is added, the quality of the wine may be adversely affected. Dose levels of more than 250 mg/l sometimes produce noticeable changes in wine taste and odor.
Sodium bisulfite is an inexpensive source of sulfur dioxide for small wineries. It provides the same amount of sulfur dioxide as potassium metabisulfite, but the sodium compound is less expensive. Sodium bisulfite is mixed with water and used for sterilizing all kinds of winemaking equipment and for wet barrel storage. Since it adds sodium, this material is usually not used as a source of sulfur dioxide in wine. Both potassium metabisulfite and sodium bisulfite are very sensitive to water, and both compounds should always be stored in tightly sealed containers.
Sparkolloid is a proprietary material manufactured by Scott Laboratories, and it is the material of choice for clarifying white and blush wines. Sparkolloid is one of the more benign fining materials, and when used in reasonable quantities, it seldom strips wine flavors or aromas. It is also used as a topping material following bentonite to help settle the bentonite lees. Sparkolloid produces very fine lees, and the lees settle out of the wine slowly. Consequently, this material should not be used less than 30 days before bottling time, or small amounts may precipitate later in the bottles. Many winemakers allow for an eight-week settling time just to be on the safe side. A solution is made by stirring Sparkolloid powder into boiling water. After the powder is added, the mixture should be boiled for an additional 20 minutes. The hot Sparkolloid solution is then added to the wine and stirred well.
Tartaric acid is the best material for raising the acidity of juice or wines made from grapes. Large acid adjustments should be made before fermentation is started. About four grams of tartaric acid per gallon of juice will raise the TA about 0.1 percent. But, calculated acid additions are seldom accurate, so calculated acid values should not be relied upon. A small sample should be tested before making acid additions to the large batch. Care must be taken when tartaric acid is added to wine late in the winemaking process because the wine may need to be cold stabilized again. Otherwise, tartrate crystals may form in the bottled wine.
Winemakers add materials to wine throughout the winemaking process to improve color, clarity, stability and general wine quality. Each material can affect wine characteristics differently, and often one characteristic is improved at the expense of another. Some winemaking experience is needed before some of these winemaking materials can be used effectively.