Cruddy Corks – Fining, Filtration, and Cold Stabilization

Stonestreet Cork

Lately, due to the popularity and character of a great find, the Stonestreet Alexander Mountain Estate Cabernet Sauvignon 2006, I have spoken with a number of customers expressing concerns about residue and crystals that they have found on their corks and in their glasses. (See the picture of the cork above.)  Appearance of residue is generally not considered a flaw, but rather an indication of a winemaker’s choices in production.  Discussions about deposits in wine seem to be a hot topic in my world right now.  So this is probably a great time to impart a little information about fining, filtering and cold stabilization of wine.

The article below was written by Jordan Ross, a writer an viticultural academic who studied at UC Davis and who has worked extensively in the wine business. Jordan does a great job of explaining the ins and outs of fining and filtration and references some very popular wines and winemakers as examples. If you are really curious, it will give you some ideas on wines to seek out so you can learn more by pulling a cork or two.

Fining and Filtration: The True Story
Jordan P. Ross

Connoisseurs, members of the wine trade and particularly wine critics, are under the increasingly popular notion that unfined and/or unfiltered wines, because they are manipulated less and therefore considered more authentic, are superior in quality.

Based on the experiences of some of the best winemakers in California, it can be concluded that wines of extraordinary quality are produced both with and without fining and filtration. Since these practices do not necessarily guarantee or compromise wine quality, the best way to evaluate a wine is by drinking it. Nonetheless, some producers trying to exploit the trend, attempt to boost sales by pandering to influential wine critics. But what the critics do not realize is that fining and filtration are indispensable to the winemaking craft and, used properly, can improve wine quality.

After a wine completes fermentation, yeast, bacteria and fragments of grape cells are in suspension which make the wine cloudy. During aging, the wine clarifies as gravity pulls these particles to the bottom of the oak barrel or stainless steel tank, producing a sediment called “lees.” When this natural settling is insufficient to achieve a clear wine, fining or filtration is necessary prior to bottling.

FiningFining and filtration are both used for clarifying a wine as well as to “stabilize” a wine. A stable wine will not undergo undesirable changes resulting from extremes of storage conditions such as temperature. It is not enough for a bottled wine to be   visually brilliant because certain particles present in excess (tannin,   protein) can become insoluble during the first 2-3 years of bottle aging, making the wine cloudy and, over time, leaving a deposit. Fining, a practice   as old as winemaking itself, specifically removes tannins and proteins, ensuring its future clarity.Common fining agents for white wines are milk, casein (the protein found in milk), and isinglass (from the air bladder of sturgeons). Bentonite is a special fining agent added to remove protein in white wines. Otherwise, if the wine reaches a temperature of 80-90 degrees F, the proteins may denature (same as heating an egg white), appearing as a haze in the bottled wine. Bentonite is natural clay, carrying a negative charge which binds with and removes proteins, which are positively charged. Winemakers add the absolute minimum amount of bentonite because it can strip aroma compounds attached to the proteins.Red wines do not present problems with protein instability because the excess tannins react with and precipitate the proteins during fermentation. Fining agents also are used to clarify a red wine to the point where only a light filtration or no filtration at all is needed prior to bottling. But their more common use in red wines is to remove tannins, which reduces harshness. Common fining agents for red wines are animal proteins such as egg whites, gelatin and milk, all of which are positively charged. The attraction resulting from these opposite charges causes these substances to precipitate. The wine is then racked to separate the clear wine from these fining lees.

Filtration
Filtration, a technique used for clarification and microbiological stabilization was introduced to winemaking only 30-40 years ago. The advantage of filtration over fining is that it can clarify a young, cloudy wine faster and more efficiently than fining. It clarifies by removing particles in suspension that cause cloudiness. Filtration not only clarifies visually, but by removing suspended particles can, from a sensory standpoint, make the fruit characteristics of a wine clearer and more vivid. Since some of these particles are yeast and bacteria, filtration plays an important role in the “microbiological” stability of a wine by eliminating the risk that these microbes will ferment undetectable quantities of sugar (or other food sources) still present after bottling.Filtration works by forcing a cloudy wine through a filter bed consisting of tiny pores which trap impurities. The most common materials used are cellulose fibers which are packed together into a pad. As the wine passes through, the fibers trap particles due to their negative charge and sieve-like effect. How densely the fibers are packed together determines the pore size and whether the filtration is rough, medium or sterile. A sterile or membrane filter, the most extreme filtration, is composed of cellulose fibers compressed to create pores in the filter bed small enough to entrap yeast and the considerably smaller malolactic bacteria.

The Influence of Malolactic Fermentation


A key factor in determining the need to filter is whether or not the wine has undergone malolactic fermentation (MLF). This applies to white wines only, since all red wines undergo MLF. Unlike the alcoholic or primary fermentation in which yeast convert sugar to alcohol and carbon dioxide, the malolactic or secondary fermentation is carried out by bacteria which consume the wine’s malic acid, producing lactic acid and carbon dioxide. Since lactic acid is a weaker acid, the net effect is a decrease in total acidity, giving the wine a softer, more elegant mouthfeel. Another important by-product is diacetyl, the compound giving wine its “buttery” aroma. The MLF does, however, diminish the wine’s youthful fruitiness which is why it is rarely used for wines such as Sauvignon blanc, Riesling or Chenin blanc. Once the MLF is complete, the malolactic bacteria can remain in the wine because there is nothing left to eat. A filtration may not only aerate and therefore oxidize a white wine but may also strip the wine of desirable flavor and aroma compounds.

Chardonnays from Burgundy and California’s coastal regions (Carneros, Russian River, Santa Barbara) typically undergo complete MLF’s. These colder climates produce grapes with higher acid levels which withstand the acid-lowering effects of the MLF, and therefore benefit from the stylistic changes. Since all of the malic acid is consumed, these wines do not need to be filtered since the malolactic bacteria have nothing left to eat.

In California’s warmer growing regions (parts of Dry Creek, Alexander and Napa Valleys) where grapes are harvested with lower acidity levels, a full MLF will drop the acidity even more, resulting in flabby wines which deteriorate rapidly after bottling. The winemaker arrests the MLF by chilling the wine or adding sulfur, both of which inhibit the malolactic bacteria. A partial MLF gives some of the stylistic benefits but leaves malic acid behind. The malolactic bacteria present in the wine pose a risk because if they ferment the remaining malic acid in the bottled wine, the carbon dioxide produced will make the wine fizzy. Even the winemaker most ardently opposed to filtration must filter this wine to remove malolactic bacteria.

Winery Size


Another factor influencing the filtration decision is the size of the winery. Small producers making a few thousand cases of l00% malolactic Chardonnay can get away without bentonite fining and certainly without filtration. The brilliant clarity resulting from filtration may not be as important given that their customers are more sophisticated and will accept the slightly cloudy appearance of a non-filtered Chardonnay as evidence of minimal handling. On the other hand, a producer bottling l00,000 cases of a $9.99 Chardonnay will expect these wines to be floor-stacked at Safeway. Without bentonite fining, these wines will throw a protein haze if temperatures in the Safeway delivery truck, warehouse or trunk of a customer’s car exceed 90 degrees F.

Producing an unfined or unfiltered wine at a small winery is considerably easier because the winemaker is overseeing, if not actually performing all steps in winemaking. One such step is racking which is the drawing off of the more or less clear wine from the lees. A Cabernet Sauvignon, for example, is racked four times per year with each successive racking yielding a clearer wine. As long as the racking is done properly, after two years of barrel aging the wine will be sufficiently clear to bottle without filtering. The reality of larger wineries is that instead of 50 barrels, there are l,000 barrels, requiring the winemaker to delegate the racking to several cellar workers making it impossible to have adequate control over this important step in clarification. The larger the production, the less flexibility the winemaker has. Each fining or filtration step removes some amount (difficult to quantify) of aroma from the wine but will presumably add a greater amount in terms of insurance against cloudiness, haze or sediment formation, or microbiological instability.

Pros and Cons


Dave Ramey, the winemaker at Rudd Estate believes in fining as a way to minimize and hopefully eliminate filtration. “I have never bottled a wine without fining it. Fining is a time-honored, traditional, gentle technique and an indispensable aid to making fine wine,” he explains. For his Cabernet Sauvignon, he fines with egg whites. Ramey reports that, “The primary purpose of egg white fining red wine is to clarify the wine and therefore eliminate filtration. A secondary benefit is to specifically target tannins; this polishes, refines and finishes the wine, making it more supple and silky. The third is to remove unstable tannins which would otherwise throw a deposit after two to three years just when the wines are being consumed in restaurants.” Ramey also fines Chardonnay and Sauvignon blanc (both l00% malolactic) with isinglass and milk to make filtration unnecessary and to achieve the same refinement and suppleness he strives for in his red wines.

Don Van Staaveren, Winemaker at Artesa Winery in Carneros, made a Bordeaux-style Cabernet Sauvignon called “Cinq Cepages” while winemaker at Chateau St. Jean. Van Staaveren filters his Cabernet Sauvignon but has not fined a wine since l985. He says, “I am against fining. Although it pulls out tannins, preventing sediment formation, some of these tannins contribute to aging and mouthfeel and you want to hang on to as much of that as possible.”

To eliminate fining, he takes   several precautions during fermentation to extract sufficient tannin while   avoiding astringency. Van Staaveren explains, “We crush lightly, leaving more   whole berries. Low speed pumpovers and gentle punch downs help us to avoid   grinding the pomace. By incorporating air into these practices, we get the   phenols to polymerize, softening the wine. I try to take care of the problems   during fermentation that would require fining later on.” As to filtration, “there   is enough extract and power in our Cabernet so I am not so concerned with   what we may lose in filtration.”

Russian Roulette?

In the early 90’s, Chateau St. Jean produced more than l00, 000 cases of a $9.99 Chardonnay. Van Staaveren cites the microbiological risks of not filtering such a wine, “If you do not filter a Chardonnay that contains some residual sugar and has not completed malolactic fermentation, you might as well play Russian Roulette. For our white wines in general, we use one quarter of the recommended bentonite. Our wines are not squeaky clean; they will throw a protein haze if accidentally heated.” Van Staaveren continues: “The more limited, and therefore exclusive the wine, the more flexibility the winemaker has. Unfined and/or unfiltered wines are bought by sophisticated clientele and for them, slightly turbid or opaque is OK.” Van Staaveren casts a weary eye toward the proliferation of claims in this area. “It has become fashionable to say ‘unfined’ or ‘unfiltered’. At some level it can generate case sales. There is a place for fining and filtration. They are tools; it is how you use them, how you apply the technology and how they fit your wine style.”
Silver Oaks Cellars is an example of fining and filtration practices being dependent on a wine’s aging regime. The late Justin Meyer, former winemaker explained, “We age our wines for 30 months in oak barrels during which time the sediment settles out naturally and the wine develops finesse. The extra year of aging accomplishes what others accomplish with fining.”

But, this extra year of aging caused Meyer to take precautions before bottling. “A lot of things can happen in 30 months,” he said. Meyer is referring to the growth of microbes such as acetobacter which converts alcohol to vinegar, lactobacillus which produces volatile acidity and Brettanomyces (“barnyard” aromas) all of which spoil a wine unless removed by sterile filtration. He adds, “Even a red wine through malolactic fermentation with no residual sugar – if you bottle without sterile filtering, I believe you’re sitting on a keg of dynamite.” Meyer added, “We have conducted experiments putting some wines through a sterile filtration and some not and have had difficulty telling the difference. No one knows how much character is actually removed by filtration. It is a myth that unfiltered wines are inherently better.”
David Graves, General Partner at Saintsbury, produces outstanding Pinot Noir and Chardonnay. Although Saintsbury is moving in the unfined and unfiltered direction, Graves comments echo Meyer’s, “Non-filtered wine is not always better than filtered wine. High quality is equated with non-filtration. This is nonsense because there are microbiological risks.” Graves concludes that, “for our wines this is the best way, but I wouldn’t recommend it to others. In l993, Saintsbury winemaker Bill Knuttel experimented with l,000 cases of non-filtered Chardonnay. “We preferred it over the filtered. It had a rounder mouthfeel. The fruit was not quite as clear but it had more complexity,” according to Graves.  The added mouthfeel is believed to be caused by the presence of dead yeast cells which remain in the wine. It is believed that as the yeast cells break open (autolysis), they release certain constituents which improve texture and ageability by protecting the wine from the damaging effects of oxygen.

Newton Vineyards in St. Helena has produced an unfiltered Chardonnay for many years. Former Winemaker John Kongsgaard, patterned this Chardonnay after the European example. He explains, “Many of the great white Burgundies are unfined and unfiltered. We are unlearning the local traditions in favor of the older traditions.” Newton does not fine or filter its wines and Kongsgaard cautions that there are prerequisites, “To practice these methods, the wine must be microbiologically stable, meaning all of the sugar and malic acid are gone. You never have zero sugar and zero malic acid, so it is a guess. Every practitioner has to have some minimum target level which varies from vintage to vintage and winery to winery. It is not an absolute number.”

Tom Rochioli, winemaker at Rochioli Vineyard occasionally filters but never fines his Pinot Noir. He comments, “Pinot Noir is different by nature. Our Pinot Noir has a very low level of tannin so fining is unnecessary. I’m lucky; our wines clarify easily as well. We usually have relatively low pH readings and that is important to ensure a healthy fermentation, minimize sulfur additions and combat negative microbial growth.”
Flavor Clarity Rochioli’s views on filtration are interesting. “I do not see filtration as a negative. It can be positive – it puts the finishing touches on a wine. I have actually preferred some of the wines in the vintages which I have filtered. They can have cleaner and more pure flavors; the wine just seems more polished. The unfiltered wines can have a ruddy, gritty texture lacking finesse. This is a major factor in determining whether I filter or not.” Rochioli points out that all filtrations are not equal, “I do not equate wine quality with non-filtration but wine quality with the quality of the filtration. You can ruin a wine by pounding it through the filter at high pressures, and with a low flow rate you begin churning and aerating the wine.” Rochioli is quick to add, “I am speaking about our estate Pinot Noir. If I bought grapes from a ranch down the road, it could be an entirely different situation.”

Rochioli also produces terrific Sauvignon blanc from a vineyard planted in l959. He explains the challenges in producing an unfined or unfiltered Sauvignon blanc, “We must fine and filter Sauvignon blanc. The grape has higher levels of solids and proteins which impede settling requiring two finings with bentonite. Isinglass is also used to polish the wine prior to bottling. It is the only wine we sterile filter because I choose not to complete the malolactic fermentation.

Ridge Winemaker Paul Draper has been producing Zinfandel for over 25 years. He often fines but never filters his Zins, and asserts that, “Careful fining and filtration have been a part of fine winemaking for many years.” He says that there is nothing inherently wrong with these techniques. “We fine 60-70% of our Zinfandels. We do not fine for visual clarity but for flavor clarity because the flavors of the wine are muddied, not clear-cut. Low levels of egg whites can lift that veil and add further definition.”

Draper stresses the importance of the fermentation in fining decisions,“The difficulty or ease of tannin extraction is different each year. You have to get a feel for this as early as possible in the vintage so you can assess how best to ferment it. The key is to avoid over-extraction of tannins because there is no simple correction for over-extraction. Fining later on will never make the wine as good as if you had gotten the tannin balance right in the fermentor.”

Zinfandel presents an added challenge because it is harvested at high sugar levels. The subsequent higher levels of alcohol can kill off the yeast before they ferment
all of the sugar. Without a filtration to remove these yeasts, they can
referment the residual sugar in the bottle, ruining the wine. Draper states,
“If we see enough yeast that we think will have an effect on stability, we will
filter the wine. We employ low-tech winemaking practices but high-tech lab
analysis.”

Kistler Vineyards’ Vice President Mark Bixler explains how the design of their
new winery in Forestville in l992 has enabled them to eliminate fining and
filtration: “We installed l6 stainless steel tanks, only four of which are
needed to process juice during harvest. The l2 excess tanks are solely for
settling wines.” Kistler installed this excess capacity at considerable cost to
enable their Chardonnays to age an additional 6-8 months. Not only are they
releasing wines with more bottle age but by achieving clarity during this extra
aging time, Kistler eliminates the need to filter. Most wineries without this
extra storage space are forced to remove the wine from tanks and barrels in
June or July and bottle it to make room for the harvest in September. Kistler
does not fine with bentonite. Nonetheless, the possibility for the wines to
throw a protein haze is remote since Kistler ships his wine during the cool
months of March and October; he asks distributors to use refrigerated trucks
and besides, it is unlikely that a consumer purchasing a bottle of Kistler
Chardonnay will let is bake in his/her car trunk.
Customers have also asked about a crystalline deposit they have discovered on the cork and in their glass.  I have heard customers refer to these crystals as “glass chards” or “wine diamonds”.  The crystals, which look like kosher salt, can be alarming to the uninitiated.  In reality, they are a harmless deposit of potassium bisulfate, commonly known as cream of tartar.  Potassium bisulfate is a naturally occurring salt of the grapes tartaric acid; a major contributor to a wine’s perceived tartness.  Again, intervention to eliminate these deposits is a winemaker’s decision.   A process called “cold stabilization” where the wine is chilled to near freezing will cause the potassium bisulfate to fall out of suspension.  This process occurs naturally is chilled, or aged for a period of time in the bottle.

The use of fining,  filtration and cold stabilization says more about the individual differences between wineries and winemakers than these processes reflect in wine quality. Factors such as economics, production size, vineyards and stability concerns
have a significant if not overwhelming influence on winemaking practices.  Great wines are made both with and without fining, filtration, and cold stabilization. So, if you branch out and pull corks from different places and producers, you will encounter both.  Either way, don’t be alarmed the first time you pull a “cruddy cork”.