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Wine smells of rotten eggs or burnt rubber

A stinky smell of rotten eggs or burnt rubber is the result of the production or presence of sulfide compounds in must or wine. Specifically, hydrogen sulfide (H2S) is the culprit for the stinky, rotten-egg or rotten-sewer smell while mercaptans are responsible for the burnt-rubber or rotten-cabbage smell. Volatile sulfur compounds such as H2S and mercaptans usually arise from the yeast being stressed by one or more of the listed possible causes.

Possible Causes

Corrective Actions, if any

a) Elemental sulfur on grapes

b) Excessive use of sulfite

c) Wine in contact with sulfur deposits in oak barrels

d) Nutrient deficiency

e) Extended contact with gross lees

f) Extreme fermentation temperatures

g) Yeast strain known to produce high levels of H2S

  • For mild cases, rack wine and aerate abundantly

  • For more serious cases, do not aerate wine; treat wine with dilute 1% CuSO4 solution, with Bocksin, or OptiRED for reds. If no change, try treating with activated carbon.

Elemental sulfur on grapes
Elemental sulfur on grapes is a common cause resulting from vinification using grapes that have been over-treated, or treated too close to harvest, with sulfur-based vineyard mildew and fungus inhibitors. Red winemaking is more prone to H2S problems as the juice has more prolonged contact with the grape solids that are prone to develop volatile sulfur compounds. In white winemaking, the settling of particles before yeast inoculation and alcoholic fermentation allows for the separation of the juice from many of the sulfur-contaminated particles.

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Excessive use of sulfite or wine in contact with sulfur deposits in oak barrels
Excessive use of sulfite prior to fermentation can cause similar problems as well as prolonged contact of wine with sulfur deposits in oak barrels – arising from burnt sulfur dropped inside the barrel during barrel maintenance.

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Nutrient deficiency, extended contact with gross lees, or extreme fermentation temperatures
H2S can also form during fermentation where yeast is deprived of key nutrients, for example, the juice being nitrogen deficient as a result of grapes not having ripened adequately. Other sources of this problem may result from wine, particularly white wine, left on the gross lees for too long a period, or too high of a fermentation temperature.

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Yeast strain known to produce high levels of H2S
Yeast also produces some small amount of H2S during fermentation, some strains more than others, so be sure to consult the manufacturer’s specifications on yeast strains to get a sense of what to expect. For example, the Montrachet strain is known to produce high levels of H2S. This may not necessarily be a problem, although H2S may mask key fruit aromas; however, if other unfavorable conditions exist, particularly low nutrients, then the rotten-egg smell will become more obvious.

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Corrective actions
The success of any corrective action depends on the intensity of the smell (i.e., concentration of H2S).

If H2S is barely detectable, there is a good chance that it can be reduced, and possibly eliminated, by aerating the wine, such as by racking. This has the drawback of accelerating oxidation and has to be assessed against the severity of the H2S problem.

If H2S is quite noticeable, you should immediately treat the wine with a dilute 1% copper sulfate (CuSO4) solution – prepared by dissolving 1 g of the blue-colored copper sulfate crystals in water to bring the volume to 100 mL. You need to measure the required amount of CuSO4 solution very carefully because you will need a very small volume for even the smallest correction.

Add the 1% CuSO4 solution at a rate of 0.05 mg/L of wine once fermentation has completed. That would then be 0.5 mL of solution, or approximately 10 drops using a good eyedropper, to 100 L (25 gal) of wine.

Copper sulfate reacts with hydrogen sulfide to form and precipitate copper sulfide. Before treating the wine, run extensive bench tests to establish if copper sulfate does in fact correct the fault and to determine the minimum rate of addition to correct the problem. Strictly use the minimum – no more. This is VERY IMPORTANT as copper is toxic to humans at higher levels. In the US, the legal limit is 0.5 mg/L as copper. WineMaker magazine’s Wine Wizard (a.k.a. Alison Crowe) outlines the following procedure as a bench trial.

“Label two wine glasses, one as control and one as copper. Measure about 50 mL of the wine in question into the wine glasses. Measure out 1 mL of 1% copper sulfate solution into the copper glass. Swirl each glass, let them sit for about five minutes, then smell each (do NOT taste as this is quite a bit of copper for 50 mL of wine).

If the copper glass still has the stinky smell, it goes to follow that copper sulfate will not help out your wine.

If you do find that the 1 mL of 1% copper sulfate solution does help your wine, you can hone in on the amount you should use.”

Start with the minimum rate of addition to a 1-L sample of wine. Swirl the glass, let it sit for about five minutes, then smell and taste the wine. If the stinky smell is still noticeable, increase the amount of 1% CuSO4 solution and repeat the process until the stinky smell disappear BUT do NOT exceed the maximum rate of addition. Once you have determined the amount of solution required to neutralize the stinky smell in the 1-L sample of wine, scale up the addition for the entire batch.

A safer alternative solution outlined by Tim Vandergrift, a contributing author to WineMaker and Technical Services Manager at Winexpert, Inc., uses Bocksin, a German-made product “related to the fining agent silicon dioxide (kieselsol). It immediately bonds to H2S and removes the aroma. Because it’s formulated like silicon dioxide, it acts like a fining agent, bonding to proteins in the wine, settling out and leaving sediment.” Add Bocksin at a rate of 1 mL/L of wine. Stir in gently but thoroughly and then rack the wine once the sediment has settled at the bottom. Optionally, you can filter the wine.

Another safer alternative for reds is to add natural yeast derivative nutrients, such as OptiRED, at a rate of 30 g/hL.

If the stinky smell was quite noticeable, you should not aerate the wine; otherwise, this can further compound the problem and make it irreversible. Similarly, you should treat H2S immediately as soon as detected. Oxygen will transform H2S into what is known as mercaptans and disulfides – foul-smelling compounds that cause wine to spoil. Wine afflicted with mercaptans and disulfides is best dumped down the sewer. Clearly, the best cure for H2S is prevention.

As an absolute last resort only and when other treatments are not effective, you can try reducing bad odors or flavors using activated carbon, available in black powder format. Add activated carbon at a rate of up to 25 g/hL directly to the wine and stir thoroughly. You should always perform bench tests on a sample before treating a whole batch to determine if the treatment will work and to determine the rate of addition. Too much activated carbon will strip color excessively and leave a carbon-like off-flavor. Add bentonite immediately after the activated carbon treatment, rack after a few days, and filter the wine before bottling.

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