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Choosing a Fining Agent

2010 February 15

This Study examines four commonly-used fining agents in detail: A couple are found to be effective in eliminating compounds associated with bitterness and astringency.
by Bibiana Guerra

If you place a large hook on your fishing rod, you may catch a bass. If you place a small hook, you may catch a sardine. In wines, too, various fining agents have an affinity for different types of phenolic compounds. Because the various phenolic compounds are responsible in different degrees for the perception of astringency, bitterness and color, the result can be a completely different wine solely based on the fining agent used. But how different of a wine?

Finding the answer was the goal of the study, “Gelatin, casein and potassium caseinate as distinct wine fining agents: different effects on color, phenolic compounds and sensory characeristics,” by A. Braga and others in the International Journal of Vine and Wine Sciences, 41(4):203-214, 2007. It is important to keep in mind that this study does not examine every fining agent available to the winemaker, but instead, it examines in detail four commonly used ones.

A fining agent is any exogenous compound added to a wine with the purpose of clarifying it. A clarifying agent is pretty much the same thing. The subtle difference is that the word “fining” always involves an addition whereas when you “clarify” you could be adding something or not. But why would we want to fine a wine in the first place? The brief answer could be: “Because wines are colloidal solutions or suspensions–not true solutions.” That is, they hold particles that we prefer to eliminate for stabilization, brilliancy and sensory purposes. Because the density of those particles is very close to the density of the wine itself, a spontaneous clarification would take too long, and a fining agent helps speed up the process. A longer answer would be: “We fine a wine to remove suspended materials that may cause the wine to become cloudy or develop a sediment, to eliminate or adjust sensory characteristics that we consider a fault, or to prevent the wine from deteriorating prematurely.”

But what could cause a haze, a sensory defect or a premature deterioration? There are many compounds in a wine able to do just that: yeast, bacteria, grape fragments, tartrates, proteins, pectins, phenolic compounds, sulfur compounds, copper, iron. But by far the most frequent targets are:

  1. proteins, responsible for developing cloudiness in bottled wines, and
  2. phenolic compounds, responsible for bitterness and astringency.

When the target is proteins, the fining agent tends to be a high-surface mineral compound (i.e., bentonite, diatomaceous earth, carbon). When the target is phenolic compounds, the fining agent is a protein (i.e., gelatin, casein, isinglass, egg albumin)–as is the case in the present study.

Fining Agents Evaluated

The authors compared four types of proteinaceous fining agents: solid gelatin, liquid gelatin, casein and potassium caseinate.

Proteins like to interact with the phenolic compounds in a wine in two possible ways: through the formation of hydrogen bonds and through hydrophobic interactions. This process seems to involve two steps: an initial step of association, which renders the protein-tannin complex soluble, and a second step of aggregation, in which additional molecules join the club until they render the complex insoluble and, therefore, ready to precipitate. Wine conditions, such as pH, alcohol, temperature and polysaccharides, have the ability to affect this tannin-protein complex formation, even if we do not fully understand the role of each in detail.

To be able to understand the behavior of each fining agent, the authors conducted a thorough characterization of their physical properties, including molecular weight, nitrogen content, pH and charge density. They found that all of them had slightly acidic–or almost neutral–pHs. Liquid gelatin had a little higher percentage of nitrogen than the remaining agents (nitrogen is the signature element in a protein). Solid gelatin was the one with the highest surface charge density. But the main difference among all of the fining agents was at the level of their molecular weight: casein and potassium caseinate had the smallest size (30 kilodaltons), liquid gelatin was intermediate (<43 kilodaltons) and solid gelatin was the largest of the four, comprised of fragments above 43 kilodaltons. Commercially available gelatins vary widely in their molecular weight depending on whether the hydrolysis used in their manufacture is chemical (larger sizes) or enzymatic (smaller sizes).

White Wine Results

For the white wine fining trials, the authors used a 2003 wine from the Óbidos region of Portugal, consisting of a blend of varieties not specified. The addition rates for the solid gelatin, the casein and the potassium caseinate were 8, 15 and 20 grams per 100 liters of wine, respectively. For liquid gelatin, the authors used 5 milliters per 100 liters of wine. After treating the wine with each of the four fining agents under study, the authors analyzed which tannin fraction–monomeric, oligomeric or polymeric flavanols–had been depleted the most.

The authors found that casein was the fining agent that depleted the monomeric flavanols the most. In contrast, both types of gelatins were relatively inefficient in removing this small molecular-weight fraction. Solid gelatin (above 43 kDa), followed by casein, was the most effective fining agent against oligomeric flavanols–the intermediate tannin size. Finally, liquid gelatin (below 43 kDa) was the agent that removed the most polymeric flavanols. These results are in agreement with other studies that found that proteins with lower molecular weight had greater affinity for highly polymerized tannins. The interpretation is that smaller protein molecules are more flexible than larger ones, thus better able to bend and reach the reaction centers of the tannin molecules with which they interact to form an insoluble complex.

The authors went on to study the effect of the various fining agents on the color of the white wine. To measure color, they used the CIELab nomenclature. As a remainder, there are four main CIELab coordinates: C*, L*, a* and b*. C* stands for chroma (or intensity); L* measures lightness (or clarity); a* measures “redness” (or its absence–greenness); and b* measures “yellowness” (or its absence–blueness). The authors found that both types of gelatin and casein decreased yellowness (that is, they reduced white wine color). Liquid gelatin, on the other hand, was the agent that caused the greatest increase in lightness (greatest clarifying effect).

Red Wine Results

For the red trials, the authors used a 2003 Portuguese blend from the Lisbon region (again, with varieties not specified). The rates used were slightly higher than those used for white wines (10-20 grams per 100 liters for the solid fining agents; 6 milliliters per 100 liters for liquid gelatin). Once again, they studied in detail the effect of each fining agent on monomeric, oligomeric and polymeric flavanols, as well as on anthocyanins and polymeric pigments.

As had been the case with the white wine, gelatins were not very effective in decreasing monomeric flavanols, which, in contrast, were effectively reduced by casein and potassium caseinate. Also in agreement with the results in the white wine, liquid gelatin was the most efficient fining agent to decrease oligomeric and polymeric flavanols.

When the authors tested the ability of the fining agents to preserve red wine color, liquid gelatin was the agent that brought about the greatest reduction in colored anthocyanins. This same fining agent was also the one achieving the greatest reduction in polymeric pigments, that is, anthocyanins combined with tannins. It is therefore no surprise that liquid gelatin was overall the fining agent which produced the greatest loss in color intensity (as measured by absorbance). The CIELab coordinates confirmed this latter result as the wines fined with liquid gelatin showed the highest increase in lightness (highest clarifying action) and the highest decrease in redness (highest color loss).

Sensory Characteristics of Fined Wines

To find out how the fining agents impacted the sensory characteristics of the wines the authors performed a sensory analysis using a panel of nine trained judges. The judges evaluated specific descriptors, such as “color intensity,” “hue,” “aromatic intensity,” “aromatic quality,” “taste intensity,” “taste quality,” “fullness,” “astringency” and “global appreciation,” using a scale from 1 (low) to 7 (high). As we can see, some descriptors (i.e., global appreciation, aroma and taste quality) involved a higher amount of subjectivity than others (i.e., color intensity, fullness or astringency). The wines were evaluated blindly but only once.

For the white wine under study, the authors found that liquid gelatin rendered the best color and clarity, but solid gelatin was the agent that preserved aroma intensity the most. As for casein and potassium caseinate, both behaved very similarly and resulted in the highest fullness and global appreciation scores.

For the red wine, color intensity, as well as aroma intensity, was highest with casein. However, it was the wine fined with liquid gelatin that was characterized as more astringent, with higher aroma quality and with better global appreciation.

The latter result–the fact that wines fined with liquid gelatin were characterized as more astringent–is not entirely expected given that liquid gelatin was also the most efficient agent against highly polymerized tannins. The authors would have greatly strengthened their sensory results had they submitted to the panel several red and several white wines. This would have allowed them to confirm that the behavior observed for each fining agent was maintained throughout a variety of wines. Also, they could have chosen the use of a more rigorous sensory technique, given that the value of terms like “global appreciation” and “quality” is not completely free of controversy.

Conclusions

The value of this paper resides in the authors applying high-resolution analytical techniques to explore the size of the phenolic compounds left in a wine after fining with various fining agents commonly used by winemakers. Even though the sensory portion of the results had some limitations, the authors were able to reach the following conclusions:

  1. A gelatin with small molecular weight fragments was more effective in depleting the larger polymerized tannin fractions–the most responsible for astringency–than a gelatin with larger fragments.
  2. Casein, and to a lesser extent potassium caseinate, was more effective in depleting the smaller monomeric fractions–the most responsible for bitterness–than the rest of the fining agents studied.
  3. The gelatin with the smaller molecular weight fragments was the one that diminished color the most, both in whites and in reds.
  4. The gelatin with the smaller molecular weight fragments was the one that provided the best clarity of the four agents studied, both in whites and in reds.

So, do you know the size of your gelatin? wbm

Bibiana Guerra , Ph.D., worked at Woodbridge by Robert Mondavi as a research winemaker and a grower educator for seven vintages. Before that, she worked at Sonoma’s Flowers Vineyards & Winery, first as an assistant winemaker (1998), then as vineyard manager (1999). She is currently a technical writer in the department of enology and viticulture at UC Davis.

8 Responses leave one →
  1. PaulGatti permalink
    March 9, 2010

    I racked my 2009 Tempranillo this past weekend, and found it to be overly tannic and astringent.Can’t think of what went wrong…Ferment
    went 11 days, max temp of 79,pressed cake twice tasting while pressing
    and didn’t taste too astringent…I’ll work on the why,but now must
    decide on the how to fix…Has anyone had any experience with fining
    agents? Should I fine now? Or rack into barrel, wait a year see where I
    stand. Most likely, I’ll try to blend it out with some other varietal.
    Opinions?

  2. Gene Fiorot permalink*
    March 9, 2010

    Considering fining a 09 Now? You must be baiting . You sly old dog you .

  3. AlbanyCellarRat permalink
    March 9, 2010

    Repost in 2011.

  4. Gene Fiorot permalink*
    March 9, 2010

    I like that “repost in 2011 ” Good one.

  5. PaulGatti permalink
    March 9, 2010

    Hopefully no repost in 2011!

  6. Gene Fiorot permalink*
    March 9, 2010

    Well, while we wait until 2011 to see if the tannins calm down how about telling us more about this wine.

  7. Shannon Hards permalink
    July 3, 2017

    Me again. You have gave me great advice in other blog posts. Thanks for that. I am very novice.

    Now my new question. There is something pink or white floating in the red. 1 micron absolute does nothing to it. Would think to try bentonite trials first, if I was winging it. What would you suggest?

  8. Gene Fiorot permalink*
    August 24, 2017

    if it is soft like a foamy yeast deposit you need to up your SO2 as you have the onset of a bacterial infection try to absorb the floating stuff and bang up the Meta.

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