To: Regional Vintners

From: Bruce Zoecklein

Subject: Fining Agents, Isinglass and Structural Balance, and Summary of Fining Agent Use

Fining agents are added to juices, wines, and sparkling wine cuvées for the purposes of enhancing clarity, color, aroma, flavor, and/or stability modification. Fining agents can be grouped according to their general nature.

Earths: bentonite, kaolin Proteins: gelatin, isinglass, caseins, pasteurized milk, albumens, yeasts Polysaccharides: alginates, gum arabic Carbons Synthetic polymers: PVPP, nylon Silica gel (silicon dioxide) Tannins Others: including metal chelators, blue fining, and enzymes

The mechanisms of action of fining agents may be electrical (charge) interaction, bond formation, and/or absorption and adsorption. In the case of electrical interaction, particles of opposite charge to the fining agents are induced to coalesce with the agent, forming larger particles. Due to its greater density, the complex eventually settles from solution.

Isinglass and Structured Balance

Wine balance can be depicted as in the following relationship: Sweet = Acid + Phenolic Elements. This relationship suggest that as the perception of sweetness increases, the perception of those elements on the righthand side of the equation will decrease. The converse is also true, as the sweetness diminishes, the perception of the acid and phenolic elements (bitterness and astringency) increases.

Isinglass is a protein fining agent which can have a significant influence on wine balance. As discussed in the Vintner's Corner Newsjournal Vol. 17, No. 1, and Enology Notes No. 41, wine balance is an important wine quality feature. Isinglass is an effective agent in modifying wine phenols and, therefore, balance.

Isinglass is a protein fining agent produced from sturgeon collagen. It is available in two forms: a prehydrolyzed form that hydrates in 20 to 30 minutes and a fibrous form of flocced isinglass. Hydration should be carried out in cool water (15° C/60° F). If prepared in hot water, isinglass undergoes partial hydrolysis, resulting in the formation of smaller molecules. The reduction in molecular weight from 140,000 to 1558,00 results in differences in fining characteristics, and the product is more gelatinlike in its activity. If the hydration method is different in the lab vs. cellar, do not expect lab and cellar results to be the same.

Isinglass is principally used in white wine fining to bring out or unmask the fruit character without significant changes in tannin levels. Isinglass is less active toward condensed tannins than either gelatin or casein. Because condensed phenolics are principally responsible for astringency, isinglass has a less dramatic effect on the reduction of both wine astringency and body than most other protein fining agents. It has the added benefit of not requiring extensive counterfining as compared with other proteinaceous fining agents. Many vintners fine with the agent after aging (particularly barrel aging) and before bottling to “round out” background astringency and produce a brilliantly clear white wine without the stripping effect seen by other protein fining agents. Isinglass is also used as a riddling aid in methode champenoise production at levels of 1.5 to 4.0 g/hL (1/81/3 lb/1,000 gal.).

Isinglass has several advantages over gelatin in fining of white wines. The agent is active at lower concentrations, produces enhanced clarification and a more brilliant wine, and is much less temperature dependent than gelatin, which shows enhanced properties at low temperature.

Isinglass does, however, have several significant drawbacks. The low density of flakes forming after addition to the wine can result in voluminous lees formation (>2%) , and particulates tend to hang on the sides of barrels and casks. Like other proteins, isinglass can degrade with time, particularly if stored warm, imparting an unpleasant, fishy odor to the slurry. For this reason, only isinglass of the highest quality should be used. No limit on the use of isinglass is imposed by either BATF for the OIV.

Summary of Fining Agent Use

• The smallest quantity of agent necessary should be used.
• Only fining agents of the highest purity, free from undesirable odors and flavors, should be used. The contact time should be limited to only that necessary for complete reaction and formation of lees; centrifugation may shorten exposure time.
• Careful laboratory trials must be carried out before cellar treatment. Laboratory fining agents should be prepared by the same method intended for cellar treatment. For example, the sheer force exerted by laboratory blenders cannot be duplicated in the cellar.
• To ensure a maximum utilization and reactivity of a fining agent, it is essential that thorough mixing of the material and juice or wine be achieved. This is best done by using a ‘Y” on the suction side of a positive displacement pump, by using a proportioning type pump, with a Guthtype tank mixer, or by using a dowel or electric stir rod for barrel mixing.
• Wines to be fined should be low in dissolved CO₂. Evolution of gas will serve to maintain particulates in solution and impede settling.
• Young wines are more “forgiving” than older wines to the action of protein fining agents.
• Lower pH wines will require less fining agent for clarification than the corresponding wine of higher pH.
• A high metal content in either the fining slurry or the wine may adversely affect flocculation and activity of the agent. Although the action of some agents such as gelatin depends on the presence of metal ions (iron), many winemakers choose to use deionized water for hydration.
• Temperature is important in reaction time; therefore, laboratory fining trials must be carried out at the same temperature as the juice or wine to be treated. Protein fining agents are more effective in removing phenolic compounds at lower vs. higher temperatures. The difference between 10° C (50° F) and 25° C (77° F) relative to phenol absorption is significant.
• The effectiveness of a fining agent depends on the agent, method of preparation and addition, levels of addition, pH, metal content, temperature, presence of CO₂, and prior wine treatments.

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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
EnologyGrape Chemistry Group Web address: www.fst.vt.edu/zoecklein/index.html
Phone: (540) 231-5325
Fax: (540) 231-9293
Email: bzoeckle@vt.edu