We are continuing on with the fourth and final part on our series on bad wines, their diagnostic, causes and treatment. Hope this info will help make the wine world a slightly better place! 😉
The Rest of the Common Wine Faults
10. Volatile Acidity
Description: While several other volatile acids (those organic acids separable by distillation) – lactic, succinic, and propionic – occur in wine, Volatile Acidity commonly (but inaccurately) is used to refer to both acetic acid and ethyl acetate. Table vinegar is 5% (50 g/L) acetic acid whereas the threshold in wine is about 0.2 g/L. Legal limits are about 1.2 to 1.5 g/L and levels above 1.5 g/L are usually frankly vinegary. Acetic acid alone has only slight impact on aroma and bouquet but ethyl acetate is often present. The nose and particularly the flavour of acetic acid is a slightly sweet, acidic, (vinegary) character and is particularly noticeable in the aftertaste where it tends to linger.
Cause: (see Ethyl Acetate). Acetic acid bacteria (Acetobacter spp.) as contaminants of slightly fermenting damaged grapes will provide a large inoculum that can quickly produce a lot of vinegar especially in an unattended red wine cap.
Prevention: See ethyl acetate.
Treatment: Wine with frank acetic acid should be sulphited as soon as possible to kill the bacteria. Then it can be blended with another wine and the acetic acid diluted to a level where it is not noticeable.
Judging: When ethyl acetate is present, acetic acid is difficult to detect because it is overwhelmed by the aggressiveness of the acetate ester and because few judges will actually taste such wine. When ethyl acetate is not evident, acetic acid V.A. at levels high enough to be identified is rather rare.
11. Diacetyl (2,3 butane dione)
Description: A buttery, rancid butter or butterscotch note in aroma and flavour.
Cause: A product of malolactic bacterial metabolism particularly in the absence of yeast lees which tend to neutralize the diacetyl produced. Frequently diacetyl results from the breakdown of citric acid after the malic has been consumed.
Prevention: Citric acid should not be added to wines with ML bacteria. Wines should remain ‘sur lie’ until MLF is completed.
Treatment: Diacetyl may be encouraged for greater butteriness. If an objectionable excess of diacetyl has formed in a wine, it may be worthwhile to store it well sulphited on another batch of clean lees.
Judging: Often an attribute, diacetyl is seldom present at levels high enough to warrant being considered more than a flaw. In reds it can be somewhat unpleasant but the wine is almost always drinkable.
If detected at levels that seem appropriate to the wine it may be considered a positive feature.
12. Brettanomyces Contamination
Description: A mousy, horsey, sweaty, wet dog, leathery, stale hamburger, barnyard character. Similar character to Belgian Lambic beer. Adds complexity at low levels.
Cause: Contamination of grapes, wines and equipment by the surface yeast, Brettanomyces spp. and its production of tetrahydropyridines.
Prevention: Regular rinsing of equipment and attention to sulphite levels.
Treatment: Unknown
Judging: Some wine purists consider ‘Brett’ a fault. At low levels it not only adds complexity but may be responsible for traditional regional characters (Rhône, Burgundy). When it occurs at levels that overwhelm fruit or varietal attributes, it should be considered a flaw. ‘Brett’ is often associated with high pH reds because it is only volatile at neutral or high pH. Its presence can be confirmed by rubbing some wine between clean hands and sniffing the palms for the characteristic meaty note. In the mouth it is most easily detected after swallowing or spitting the wine as the oral pH returns to neutral after the more acid wine disappears.
13. Chemical Contaminants
Description: Usually unpleasant, sometimes aromatic chemical character; very uninviting.
Cause: Plastics [e.g., a green garbage bag that was used to cover a fermenter; non-food grade containers]; cellar mustiness; chlorine; detergents (more likely a contaminant of the wine glass), volatile hydrocarbons (varsol, gasoline, kerosene,etc.) stored nearby.
Prevention is obvious.
Treatment: No practical solution.
Judging: Their presence is a fault and renders a wine undrinkable. They fully justify not tasting the wine. Recommend winemaker discard any wine that may have been contaminated with volatiles.
14. Additive Overuse
a) High Sulphur Dioxide
Description: An acrid, tingling to burning sensation accompanied by the smell of burnt match heads or wet wool. In the mouth, a soapy character.
Cause: Prevention, Treatment. Although small amounts of SO2 are produced during fermentation, high levels are always the result of inappropriate additions by the winemaker. Intense, fresh, pungent SO2 has been recently added in excess; soapy, wet wool character indicates oversulphiting earlier.
Judging: If SO2 is noticeably pungent it should be considered a flaw and the wine marked down for its presence. Similarly, a wet wool character is a flaw, though it seems appropriate to assess it as less offensive. Recently added SO2 can be made more evident by capping glass with hand and agitating wine before sniffing it.
b). High Sorbate (2,3 hexadienoic acid)
Description: A chemical, bubblegum character to which many people are oblivious, others highly sensitive.
Cause: Use of excess potassium sorbate to prevent renewed yeast fermentation. The accepted effective dosage of sorbate is 200 mg/L (300 mg/L is BATF maximum allowed).
Prevention: Careful weighing of sorbate.
Treatment: None known.
Judging: (Judges should be aware of their personal threshold and if they are sensitive much below the effective dosage that fact should be communicated to their judging partner when sorbate is suspected.) Wine with excess sorbate indicates poor management and it should be considered a flaw if its impact is insignificant or a fault if it overpowers the natural character of the wine. Excess sorbate is very unlikely to render a wine undrinkable.
Summary of Important Points
Flaw: minor departure from an acceptable norm. Wine usually drinkable.
Usually flaws – SO2, VA., Brett, Diacetyl, Sorbate, sub-threshold levels of reduced sulphur compounds.
Fault: major departure from an acceptable norm. Wines usually undrinkable.
Usually faults – acetaldehyde, ethyl acetate, TCA, geranium, organoleptically obvious levels of reduced sulphur compounds.
Most difficult to diagnose correctly without testing: reduced sulphur compounds and Brett.
Essential tests: improvement with penny (H2S, mercaptans); rubbing sample between hands and sniffing (Brett).
This concludes our little adventure with “bad”, faulty or flawed wines. Let me know of your experiences with unfortunately making bad wines and how you were able to either fix the problem or what you learned from it. Sharing our experiences is the best way to learn and prevent some of us from making a pile of wine fit for the drains…
To good wine drinking…cheers!