Enology Notes #46, May 17, 2002
To: Regional Vintners
From: Bruce Zoecklein
Subject: Gelatin Fining Agents continued: Alginates, Casein, and Milk
The most commonly used polysaccharides for fining are alginates. Alginic acid or algin is a structural polymer in the cell wall of algae. Commercially, it is extracted from marine brown algae. Alginic acid exists as a high molecular weight, long-chained polymeric salt of (1) ß-1,4-D-manuronic acid and L-guluronic acid, (2) D-manuronic, and (3) alternating segments of monomers of both 1 and 2.
Alginic acids are positively charged and are usually bound to some inert carrier such as diatomaceous earth to facilitate settling. Reactivity and clarification is best accomplished if the juice or wine pH is less than 3.5. Clarification may be accelerated with small additions of counterfining agents such as gelatin or bentonite. Some proprietary products include 5 to 10% (wt/wt) gelatin.
The principal protein in milk, casein occurs in solutions as a positively charged macromolecule with a molecular weight of approximately 375,000. It is presently available in dry form as (1) purified milk casein which is insoluble in acid but soluble in alkali solutions, and (2) sodium or potassium caseinate which is soluble in water. Some proprietary caseinates contain potassium bicarbonate to enhance solubility of the casein and its salts in water. Caseinate can simply be hydrated with water before use, but milk casein must first be dissolved in water at a pH greater than 8.0. Regardless of the particular casein or casein preparation, the dry form should be fully hydrated in water, never juice or wine, before use. At wine pH, casein flocculates, and the resulting precipitate absorbs and mechanically removes suspended material as it settles.
In general, casein is used in white wines and sherries to reduce oxidized (brown) color and character. Its use is not uncommon in Burgundy, particularly in white wines that have spent a second winter in the cellar.
Casein has been used to impede or prevent pinking in susceptible wines such as Chardonnay or Pinot Blanc. It is also used as a substitute for carbon in color modification in juice and white wines, and in reducing or removing dark color and cooked flavor from sherry. Although not as effective as carbon, casein does not catalyze the oxidative deterioration associated with the use of carbon in wine. Casein reduces the concentration of both copper (by up to 45%) and iron (by 60%).
As in the case of gelatin fining, casein finings of white wine are often preceded by tannic acid or silica dioxide additions. In this case, however, the ratio of tannic acid to casein should be 0.5:1 (wt/wt). Such additions are usually made approximately 24 hours before planned casein addition.
Use of casein for clarification may not yield the desired results. However, when used for this purpose, it is usually prepared in more concentrated form. The use of working solutions prepared in concentrations of at least 25 g/L appears to improve clarification.
Only the purest available grade of casein should be used so as not to impart off flavors and characters to the wine. Addition levels to wines usually range from 1.25 to 24 g/hL (1/8 to 2 lb/1,000 gal) depending on the purpose and the form used. In laboratory trials, casein is frequently pipetted to the floor of the fining vessel, then mixed by shaking. This avoids the formation of clots on the wine surface. Neither BATF nor OIV regulate the use of casein.
Pasteurized milk is approved for additions into white wines and sherry by BATF. The purposes are the same as those listed under casein, although use is limited to no more than 2.0 L of whole or skim milk per 1,000 L (0.2% vol/vol).
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Dr. Bruce Zoecklein
Associate Professor and Enology Specialist
Head Enology-Grape Chemistry Group
Department of Food Science and Technology
Virginia Tech
Blacksburg VA 24061
Enology-Grape Chemistry Group Web address: www.fst.vt.edu/zoecklein/index.html
Phone: (540) 231-5325
Fax: (540) 231-9293
Email: bzoeckle@vt.edu