Commercial winemaking has improved so widely that it is now quite uncommon to find a wine that is flawed beyond consumption. Unacceptable wines do exist, however, particularly among those made: in newly-emerging wine regions; or by neophyte winemakers; or even occasionally by well-respected winemakers.
A brief discussion of the more common wine faults should help wine consumers and winebloggers in identifying and understanding them. Winemakers will require far greater detail.
The following is not intended as a complete guide to resolving wine problems. It is merely an abbreviated summary. Serious winemakers should refer to respected industry publications for the details of selecting the appropriate treatment method, doses and negative effects that can result from each kind of treatment. Knowledgeable winemakers conduct laboratory tests to determine the best materials and dosages to achieve a desired result for each wine. The references at the end of this article serve as a starting point in such deliberations.
Public concern about sulfur dioxide (SO2) is largely unsupported by the technical reality. While SO2 is a natural byproduct of fermentation, not enough of it is produced in this way to adequately protect the wine from oxidation and microbial infection.
That said, there was a tendency to overdose wine with SO2 30-35 years ago, and that is probably what led to current health concerns. A lot has been learned since then.
At this time there is no excuse for an offensively high level of free sulfur dioxide (FSO2). The technical information regarding minimum levels needed for protection has been widely disseminated for some 25-30 years. Total SO2 (TSO2) is FSO2 plus the SO2 in several molecular forms bound to other compounds in the wine. A very small fraction exists in a gaseous, or molecular, state. Only 8 ppm in this gaseous state is required for protection from oxidation and microbial stability. The amount of FSO2 needed to provide that level varies with the wine’s pH and processing status.
Red wines on yeast lees in barrel may not need attention to FSO2 levels because the highly reductive environment created by microbial action within the lees bed prevents oxidation. (This last tactic should not be pursued by amateurs.) After malo-lactic fermentation is completed and red wine is racked off the yeast lees and returned to barrel, a maintenance level of 25-30 ppm FSO2 must be maintained.
White wine in stainless steel tanks, after it has been racked off the fermentation lees, requires an FSO2 of 30-35 ppm, in addition to an inert gas blanket, to prevent bacterial development and oxidation. White wine stored in plastic tanks will need more because plastic tanks breathe air, the same as all container materials, just faster. That’s why wine should not be stored in plastic tanks for more than 3-6 months, in this writer’s opinion and even then, special attention needs to be paid to maintenance of an adequate FSO2 level.
FSO2 levels needed when the wine is bottled are different. For a finished red wine typically at 3.4-3.6 pH, 30-40 ppm of FSO2 is needed. A dry white wine at 3.3-3.4 pH requires 25-35 ppm FSO2.
However, if the wine has residual sugar, a larger dose of FSO2 will be needed because some of the FSO2 binds to the sugar and is thus unavailable for microbial control. For an example, a White Riesling finished at 3.3 pH and 3% residual sugar might need 50 ppm FSO2 in the bottle for adequate protection.
An additional allowance needs to be made if the winery has bottling equipment that permits some oxygenation during bottling. Modern monobloc systems apply a protective blanket of nitrogen (usually, although CO2 may be wanted to add a spritz) during filling and corking. For unprotected manual filling such as by a gravity-fed 6-spout filler, the FSO2 level prior to bottling may have to be increased by as much as 50% or more.
Some purist winemakers tout that a wine has no SO2 added. OK for them, provided the wine was sterile-filtered immediately after fermentation, and they have a sophisticated bottling line with all of the bells and whistles to prevent oxygen uptake. Unfortunately, most of the “no SO2“ claimants are very small wineries who cannot afford such equipment. They don’t sterile filter! The consumer has to make sure the finished wine isn’t cloudy, which may be a good indication there are undesirable organisms swimming around in it.
SO2 may be added as compressed gas (liquid) or in the form of potassium metabisulfite (PMB, K2S2O5) crystals or tablets. Determination of appropriate SO2 additions is further confused by the fact that the winemaker is adding TSO2 as PMB and the wine’s pH will determine how much of it survives as free sulfur dioxide (FSO2) initially.
Measure FSO2. Calculate how many ppm are needed to bring FSO2 up to the protective amount (see table). Calculate TSO2 needed by using the Ratio in the table. To increase the TSO2 of 100 gallons of wine by 100 ppm, add 65.7 grams, or 2.32 ounces of PMB.
This condition usually comes from excessive aeration after fermentation has finished and CO2 content is down. It can happen in tank, especially plastic, but more commonly in barrel or during filtration. The taste is like sherry, which is intentionally oxidized.
Remedies: Maintenance of FSO2 content is basic to prevention. Corrective actions include fining by casein, deodorizing charcoal, or PVPP. The choice of which one and how large a dose should be determined by bench-testing alternatives because of differing effects on color and odor removal.
VA is the result of a troubled fermentation. The root cause may be: high temperature in the cap; nutrient deficiency because of advanced ripeness or juice fining; acetabacter bacteria (usually carried by fruit flies); and wild yeast (from the vineyard). VA consists mostly of three compounds in varying percentage distributions: hydrogen sulfide (H2S), acetic acid and ethyl acetate. H2S smells like rotten eggs. Acetic acid is vinegar, and smells/tastes like it. Ethyl acetate is a volatile ester that smells like nail polish remover.
Remedies: Control of fermentation temperature is the most important measure to avoid formation of VA. That entails both effective use of cooling jackets on tanks and punchdown/pumpover to avoid excessive cap temperature. Suppression of unwanted wild yeasts and bacteria; minimization of sulfur residue on the grapes (really difficult for practitioners of organic and biodynamic farming practices because of their reliance on elemental sulfur sprays); provision of adequate nutrients including nitrogen and B Complex vitamins (especially pantothenic acid); and meticulous winery sanitation are all important tactics.
Once the fermentation produces VA, it is crucial to begin immediate corrective action. Treatment with copper sulfate removes the H2S. Aeration of the must allows the volatile compounds to boil off. Addition of DAP (nitrogen) and yeast hulls (B Complex) will correct the nutrient deficiency. Providing temperature control by cooling and frequently immersing the cap in red wine will enable the yeast to perform more efficiently.
A small dose of TSO2 , such as 25 ppm, may be added to the juice at pressing to suppress growth of wild yeasts and bacteria until the selected yeast strain can dominate fermentation. More at this stage is unadvisable. If fermentation by wild yeast is desired, then no SO2 addition should be made until after fermentation is complete.
If a wine still shows VA after application of the in-fermentation remedies, it may be necessary to fine with deodorizing charcoal or bentonite. Filtering by reverse osmosis is another, and more controllable, treatment.
H2S, hydrogen sulfide, can be generated by yeasts during fermentation. The smell is like rotten eggs, and it is detectable in extremely small amounts. In some fermentations, it may be difficult to pin down which tank it‘s coming from. The search is made more difficult by the acute sensory fatigue caused by H2S.
Remedies: It is important to remove the H2S immediately using copper sulfate. Federal regulations place a limit on how much can be used. At the same time, nitrogen in the form of diammonium phosphate (DAP) and freeze-dried yeast hulls, or one of the proprietary nutrition products, should be added to correct the nitrogen and Vitamin B Complex deficiencies. Fermentation temperature needs to be brought under control. Aeration of the must will help remove the H2S.
Elemental sulfur applied to control fungi in the vineyard is the most frequent cause of H2S production in the winery. Less reliance on sulfur after veraison, and especially in the month preceding harvest, will help reduce the amount of sulfur coming into the winery on the grapes.
Grapes that are very ripe likely will be nitrogen-deficient. The grape’s free amino nitrogen (FAN) content is diminished. The yeast, in its quest for nitrogen, breaks down proteins to get at their nitrogen. In the process, sulfur is liberated from most of them, enabling production of H2S.
So too, white grape juice that has been fined with bentonite (hydrated aluminum silicate, montmorillonite clay) prior to fermentation will present a nitrogen deficiency, because the fining removes proteins. Add DAP and yeast hulls, or one of the proprietary nutrition blends prior to inoculation.
The wine has a strong aroma of corks. A miniscule amount can be attractive; a lot is obnoxious. The offending compound is 2,4,6-trichloroanisole (TCA). Its presence is most frequently attributed to sanitation of wine corks with SO2. Upwards of 5% of wines have suffered this condition in the past, leading to development of plastic cork substitutes and screw-top closures. Different sterilizing procedures have been developed for corks, resulting in substantial reduction of the corkiness problem.
Remedies: If you are the winemaker, change cork suppliers. If you are a consumer, demand another bottle from the sommelier, after inviting the sommelier to taste the offending wine for himself/herself. There is no other remedy beyond free replacement, inasmuch as the condition develops after the wine is in bottle. In most cases, the distributor will back bill the winery for the bad bottle and give the restaurant a credit or refund.
Largely a phenomenon of the past but, sorry to say, still encountered occasionally with new producers. The taste comes from paper filter sheets used in a plate-and-frame filter without subjecting them to a citric acid solution pre-rinse.
Remedy: After setting up the press, circulate a citric acid solution through them, followed by a clean water rinse.
Brettanamyces Bruxellensis is a wild spoilage yeast. It causes an odor sometimes called “sweaty horse blanket.” The yeast produces three compounds, each of which bears a group of odors. 4-ethylphenol characters are band-aids, antiseptic, barnyard, and/or horse stable. 4-ethylguaiacol conveys bacon, spice, cloves, and/or smoke. Isovaleric acid evokes sweaty saddle, rancid, and/or cheese.
Presence in differing ratios creates differing odor sensations. A tiny little bit can be an attractive complexing factor. More is not pleasant.
Brettanomyces originates in the vineyard, and some vineyards characteristically have more of it than others. Once inside the winery, “Brett” resides on virtually every surface. Wines become contaminated if strict sanitation standards and protective SO2 content are not maintained.
Brett may also enter in purchased used barrels that are contaminated. It is important to sanitize incoming used barrels by “turning and toasting” them. Unfortunately, additional toasting thermosets more of the oak resin, thus locking up more of the oak aroma and taste, reducing their dissolution into the wine.
Remedies: “Cleanliness is next to Godliness.” Everything must be sanitized frequently: crush pad equipment, tanks, valves, hoses, filters, bottling line. Sterile filtration, SO2 additions, and dimethyl dicarbonate are among treatments that are used. Sterile filtration is not an option for red wines because it removes too much color and tannin.
Tannins are large, complex hydrocarbon molecules of varying sizes, and they assert themselves as a tactile sensation (puckering) and a bitter taste. The larger molecules (from the grape skin and barrel wood) provide astringency, while the smaller ones (from seeds and stems) lend bitterness. To some extent, astringency serves to mask bitterness.
Remedies: Preventive measures can be taken at several points. Gentle handling on the crush pad is the first. Absolutely, the grapes have to be destemmed before they are crushed. Otherwise, excessive tannins are extracted from crushed seeds, stems and peduncles.
Maceration time (holding the juice, seeds and skins for red wine at 48-50°F for 2-8 days before yeast inoculation) comes into play. Most tannin extraction occurs in the presence of alcohol. So, cold soak extracts flavor and aromatic substances before the start of fermentation and tannin extraction.
During fermentation of red wines, punching down or pumpover of the cap has to be done as gently as possible.
Treatments to reduce tannin levels in wine include fining with gelatin, isinglass, casein, bentonite, egg whites (albumin) and PVPP. In general, egg albumin is favored over gelatin (in both Bordeaux and Burgundy) because it is much gentler in its effects.
Removal of tannins will likely remove other constituents that affect flavor and aroma. Fining removes a share of all molecular sizes of tannins, the desirable soft ones as well as the offensive harsh ones. Research, that has pursued an ability to selectively remove some tannin molecular sizes without removing the others, has not yet yielded useful results. Therefore, laboratory evaluation of a range of treatment types and doses must be conducted in order to select the best one for a particular wine.
This is a problem that occurs typically with grapes that have been picked too early, or in a cooler-than-normal growing season.
Remedy: Acid content can be adjusted easily in the winery. Calcium carbonate is used for juice, potassium bicarbonate for wine. The acid that is neutralized precipitates as a solid salt which then is removed by racking or filtration. It is far better to make acid adjustments before fermentation, as the yeast will produce a different distribution of constituents at different pH levels.
For wines that are finished with some residual sugar, it is important to find the right balance between sugar and acid. Bench tests are needed for this task. For me, the wine really sings at the right balance. It’s a situation where “two plus two equals five or more” in sensory aspects. As the Germans would say, the wine is “rassig,” or “racy.” The balance point is very obvious to the taste. Too much acid and the wine seems sharp, sour. Too little acid, and the wine loses some of the fruit dominance and liveliness.
If the grapes have too much sugar and fermentation is carried to completion, the alcohol content will be too high. Wines classified as table wines have up to 14% alcohol, measured by volume. Over 14% and the wine is classified as fortified or dessert wine with a higher federal wine excise tax. For typical table wines, >14% alcohol makes the wine “hot” and perhaps unpleasant to drink.
Remedy: Reverse osmosis is an option. Alcohol is selectively removed and controllable. It has become popular in California to let some black grapes get overripe for more flavor, then to reduce the alcohol content of the wine by reverse osmosis.
Dilution of the must by water addition is not legal for grape wines (it is legal for fruit and berry wines). Rumors persist, however, about winemakers who have found ingenious ways to get water into the must.
Say you bought some wine and left it in in the car while you completed your shopping. It was a warm day, and the temperature inside the car reached 90°F+. You refrigerated the wine after you got home and it went cloudy with white flocculent. You have a wine that was not fined to remove heat-unstable proteins.
Remedy: Fine the wine with bentonite and test for stability before bottling.
You chilled a wine in the refrigerator and it goes cloudy with a pearly-, or silky-looking sheen that appears as thin needles on close inspection against a light source. The wine was not cold-stabilized to remove tartrates.
Remedy: Cold stabilize the wine by refrigerating it to 29°F for two weeks, then test for stability before bottling.
The reader will notice several points during this discussion where environmentally-popular vineyard and winery tactics are cited as responsible for wine faults. Good intentions cannot rescind the facts. Every corrective fining carries the potential of stripping the wine of flavor, color and aroma. That’s why bench testing of materials and dosages is so important. Each winemaker has to face the decision whether popularity with some wine writers, retailers and consumers is worth the risk of damaging the wine in the repair of flaws enabled by microbial activity or elemental sulfur.
Sources consulted in preparation of this post
- A Guide to the Fining of Wine (WSU Extension Manual EM016); James F. Harbertson; Washington State University – Prosser IAREC; August, 2009.
- Fining Agents for Wine; Lisa Van de Water, The Wine Lab; 1985.
- Fining and Fining Agents; draft of technical paper; Bruce Zoecklein (Univ. of Missouri-Columbia) and K.C. Fugelsang (California State University-Fresno). Unknown date.
- Knowing and Making Wine; Emile Peynaud; Wiley Interscience Publication; John Wiley & Sons; New York. 1981.
- “Review of Basics on Sulfur Dioxide”, by Clark Smith; Technical Forum paper attached to Enology Briefs, Volume I, numbers 1 and 2; Cooperative Extension Service, University of California at Davis.
- Table Wines; The Technology of Their Production; Second Edition; M.A. Amerine and M.A. Joslyn; University of California Press; Berkeley. 1970.
- The Origin and Control of Hydrogen Sulfide During Fermentation of Grape Must; P.J.A. Vos and R.S. Gray; Oude Meester Group, Ltd., R.I.T. Centre, Stellenbosch, Republic of South Africa. Vol. 30, No. 3, 1979; American Journal of Enology and Viticulture.
Photo credit: http://brettanomyces.wordpress.com