Fining Wines
Fining Wine for Astringency and Bitterness
During red wine production, the maceration process can result in extraction of excessive tannins that contribute to astringency. Astringency in wine is the drying, rough, and mouth puckering sensation. Fining to remove tannins from wine is generally done when a wine is judged too astringent; it primarily applies to red wines since the amount of tannin in white wines is negligible. Although fining is often used for press fractions with white wines. Determining whether a wine is too astringent and bitter is generally left to the winemaker's judgment.
Casein
Casein is used to reduce astringency and soften a white wine's tannin structure (i.e., removing the aggressive oak character from an over-oaked wine). In addition, casein can also be used for removing browning from oxidative reactions in white wines. Casein is prepared from milk as powdered potassium-caseinate, which is water-soluble. It is softer than gelatin or isinglass but has limited clarifying action.
Preparation of Stock Solution
Preparation of 1 percent w/v stock solution dissolve 1 gram of potassium caseinate in 100 milliliters of distilled water with stirring. The potassium salt aids in the preparation process as it is far more soluble and therefore user-friendly than the protein itself.
Wine Treatment
The temperature of the wine should be about 10 degrees C (50°F). Add the solution slowly to the wine and thoroughly mix as soon as it is added to prevent pre-mature coagulation.
Egg Whites
Egg whites (albumin) have long been used in fining wines (Figure 9.3). The active ingredient is the protein albumin and has a positively charged surface that attracts negatively charged tannins. As with other protein fining agents, albumin is recommended for softening wines with a high tannin content and excessive astringency. This fining agent is solely used for red wine fining and is considered the best for softening and polishing red wines.
Preparation of Stock Solution
To prepare a 10 percent w/v stock egg white solution from fresh eggs, break the eggs and separate the whites from the yolks. Weigh egg whites into a large beaker. Add 10 times this weight of distilled water which has been adjusted to pH 7 (using potassium carbonate) and containing 0.5 percent potassium chloride. Potassium chloride maintains the globulins in solution. Stir gently, but avoid foaming, until dissolved.
Wine Treatment
The temperature of the wine should be about 10 degrees C (50°F). Add this mixture slowly and with thorough but gentle mixing to the wine.
Gelatin
Gelatin is a good protein for fining because it is rich in proline and reacts quite readily with negatively chargedtannins.
Preparation of Stock Solution
The commonly available form of gelatin is a powder, but it can also be purchased in sheet and liquid forms. The percentage gelatin activity (normally around 30%) should be noted from the manufacturer's instructions.
Wine Treatment
Gelatin must be added to wine within a specific temperature range (see manufacture details for exact temperatures). The liquid form of gelatin can be added directly to the wine. Add the liquid to the wine slowly and with thorough but gentle mixing. Allow a 1 to 3 days for settling, then rack or filter.
Isinglass
Isinglass is a positively charged protein extract made from the swim bladder of certain fish principally used in white wine fining to bring out or unmask fruit character without large changes in phenolic levels. Isinglass has a less dramatic effect on the reduction of both wine astringency and body than most other protein fining agents.
Preparation of Stock Solution
Isinglass is available in two forms; as sheet or flocculated isinglass. The flocculated form is easiest to work with because it does not have to be rinsed to remove fishy odors. Dissolve 1 g of citric acid in about 80 mL of distilled water.
Wine Treatment
Isinglass can be utilized anytime during the wine making process. Many producers fine with isinglass after aging - before bottling - leaving the white wine clean to the taste and sparkling clear without stripping newly formed bouquet.
Polyvinylpolypyrrolidone
Polyvinylpolypyrrolidone (PVPP) is a synthetic polymer used to reduce the level of phenolic compounds associated with astringency and browning in white wine. Being polyamide, PVPP finds it greatest application in binding with and removing small monomeric phenolic species such as catechins occurring in white musts and wines. As such, PVPP has value in diminishing undesirable bitterness.
Preparation of Stock Solution
Addition slurries are prepared at 5 to 10 percent (w/v) with wine or must and mixed for a minimum of 1 hour to ensure swelling.
Wine Treatment
Polyvinylpolypyrrolidone can be added as a slurry or as a powder directly into the tank while stirring. The normal method of use is to slowly add the appropriate amount of PVPP powder to a stirred wine and leave for about 1 hour.
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