Troubleshooting Wine Kit Aroma

Before we finish shooting smelly troubles in wine kits we need to do a quick recap of the basics of troubleshooting: Almost all of these issues can be avoided if you carefully follow the instructions that came with your wine kit. Kits sometimes have procedures that contradict accepted techniques for fresh grape/fresh juice winemaking. There are a lot of reasons for this, but they all boil down to the same thing: That’s the way that the kit ferments, clears and stabilizes best, as proven by numerous lab trials. Subverting the instructions or substituting procedures should only be undertaken when you are confident that you understand all of the downstream implications of the changes you’re making.

On to the potential defects of aroma!

Wine smells like matches

Excess sulfite is characterized by a “burnt match” or “sulfur/volcano” smell, often accompanied by a sharp tickling in the nose. Typical ways that excess sulfite gets into wine is either through miscalculated additions (adding a tablespoon instead of a teaspoon) or when a carboy or primary has been cleaned or stored with sulfite solution in it and it was not rinsed properly before wine was added.

If you do encounter this smell, be sure that it is the wine you’re sniffing and not a piece of equipment that has sulfite residue on it — this can be a real issue with carboys or bottles that have been sulfited and allowed to drip dry because the opening of the vessel might have significant sulfite residue on it, even if it’s completely dry. When the wine hits the sulfite residue on the vessel it will release SO2 gas, giving the mistake impression that the whole batch is over-sulfited.

For wines that do objectively smell like a sulfur hot spring or even worse, an active volcano, it’s important to understand that the true level of sulfite can’t be determined without a proper sulfite test. Until you’ve had your wine accurately tested, do not attempt any correction of the sulfite level. Because all correction methods either oxidize or bind away the sulfite, over-correcting can become a terminal event. When in doubt test twice and correct once.

Sulfite levels in kits are typically between 15 and 50 parts per million (ppm), depending on the type of wine and the manufacturer. Consult your instructions or contact the manufacturer for the correct level in your kit.


Minor excesses of sulfite (an extra 10 or 25 PPM) can be driven off by stirring small amounts of oxygen into the wine. You can stir air into the wine with a spoon, rack it with plenty of splashing, or bubble air into it with a sanitized fish tank aerator for a short period of time. As always with such operations, test, adjust and test again to make sure you accomplished your goal. When in doubt, do one-half of your expected total of aerating and test before proceeding. Measure twice, cut once!


Larger amounts of sulfite (up to an extra 50 to 100 PPM) can be treated with a hydrogen peroxide addition. Hydrogen peroxide is a very potent oxidizer. In high concentration it is used as part of the fuel mixture in rocket engines, oxidizing the fuel so rapidly as to resemble an explosion. It does the same thing in wine (without the exploding), oxidizing the sulfite, taking it out of action. It’s so powerful that compared to stirring you would need to stir with a spoon 100 feet long moving at the speed of sound to achieve the same effect.

For every 10 ppm of sulfite to be removed in 6 gallons (23 L) of wine, add 4.2 mL of regular drugstore hydrogen peroxide. You must use a brand new bottle of 3% wt/vol USP-grade hydrogen peroxide, measure with a syringe to get accurate results, and above all, test before and after your adjustment, to make sure you’ve hit your precise target. If you’re not sure of your math do half the amount of expected adjustment and test the sulfite levels before proceeding.

The big problem with using hydrogen peroxide is that it’s very touchy. If your calculations are off by even a few drops, you will oxidize all of the sulfite, leaving the wine unprotected against microbial and oxidative spoilage.


Subtle and elegant, the art of blending is where true mastery of winemaking shows. The primary purpose of blending is to use different lots of wine to augment or improve the characteristics of the final blend, but it can also be used to ameliorate flaws — like excess sulfite. While simple to do, it’s only practical if you have a good supply of wine and the sulfite levels are not too excessive.

First, do a test on existing levels and determine your desired level. For example, if you have 6 gallons (23 L) of wine that shows 60 ppm FSO2 and your desired level is 30 ppm, it’s fairly straightforward to blend it into another 6 gallons (23 L) of the same but unsulfited wine to drop the level by roughly half. If you don’t have the same varietal on hand you could make another batch and deliberately leave out any sulfite additions, or you could use a similar varietal or typical co-blender, such as Merlot for Cabernet Sauvignon or Malbec for Shiraz.

Know when to give up

In the case of massive overdoses of sulfite (anything in excess of 100 ppm over recommended levels) there is no answer. Stirring can’t drive off enough sulfite and hydrogen peroxide doesn’t make the sulfite disappear, it simply shifts it into another form, and too high a concentration of the bound form is not legal for human consumption, and it’s not practical to make four or five extra batches to save a single batch of over-sulfited wine. It’s wine for the sewer, with apologies to sewer workers everywhere.

Wine smells like chemicals or plastic

“Chemical” aromas can be tricky. New vinyl tubing, new bungs or new plastic pails or carboys all have faint but acceptable aromas that won’t transfer to your wine. Some aromas that are inherent in wine can be mistaken for chemicals. Riesling, for instance, can have a smell similar to kerosene or even petroleum jelly. While it shouldn’t have a strong smell of oil lamps, it’s a characteristic that’s very much sought-after by lovers of fine aged Rieslings.

In addition, some yeast strains throw off a host of ketones, aldehydes, esters and sulfur compounds during fermentation, some of which can still be detected while the wine is very young. If you’re not sure you actually smell chemicals, have a wine-savvy chum blind taste the wine and assess it for you.

Clean wine?

If you accidentally introduced any of your cleaning chemicals (chlorine, detergent, caustics, free halogen sanitizers such as Iodophor) into the wine, you should discard it. While small amounts of these products may or may not be harmful to your health, there is no way to be sure, and better safe than hospitalized. There are some “no-rinse” sanitizers that may be less harmful, but unless you get written assurance from the manufacturer that it’s absolutely safe, better to discard the wine than take a chance.

The wrong cleaner

Never, ever use anything but approved winemaking cleaners and sanitizers on your equipment. All home cleaning products, even those that are labelled “99 and 44/100th’s pure” contain additives or perfumes that are not acceptable for use with wine. The aroma of home dishwashing detergent will sink straight into food-grade HDPE plastic where it will be leached out by the alcohol in wine, and stay in it forever. The worst example of this I have ever seen was 300 gallons (1,135 L) of Sangiovese that smelled of the lemony-fresh laundry soap the gentleman had used to clean his plastic fermenting barrels. The only solution? Alas, the sewer wins again.

The wrong equipment

If you used a non food-grade fermenter for your wine, you may have a real problem on your hands. In addition to causing odd plastic aromas in the wine, non food-grade buckets and pails use volatile chemicals and sometimes heavy metals such as antinomy, arsenic and lead to keep the plastic pliable and soft. They may also contain UV blockers that are toxic. The alcohol in the wine will leach these out, and could seriously jeopardize your health. Discard the wine and purchase some good food-grade wine-specific equipment.

Wine smells like Sherry or nuts

Unless you’re a squirrel, your wine is oxidized, displaying acetaldehyde character. See the treatment recommendations for browned wines in my last column (Troubleshooting Part II from the Dec 14/Jan 15 issue), but don’t hope for much. Acetaldehyde formation is a process requiring lots of oxygen, low sulfite levels and significant time. The usual culprit is ullage in the carboy, empty fermentation locks, or over-zealous racking. To prevent oxidative damage always use the recommended sulfite in your kit, top up carboys of finished wine right into the neck and make sure your airlocks are working to exclude air.

Wine smells like rotten eggs

Eggs are wonderful as a breakfast food, but they really don’t make for a good beverage. The predominant smell of eggy wine is less like a plate of over-easy and more like boiled eggs that have sat around too long — not to be indelicate, but it’s flatus we’re talking about here. It can come from several sources.

Most yeast strains produce a small amount of hydrogen sulfide (H2S) during fermentation, giving a whiff of rotten-egg. Certain yeast is more prone to large amounts of this aroma, the Montrachet strain being particularly bad. However, this is rare in wine kits, as excess H2S is usually a symptom of low nutrients in the must, or too high a level of solid grape material —conditions that don’t apply to kits as long as you follow the instructions and rack from primary too late. In addition, the amounts produced are usually driven off during the degassing phase, when CO2 coming out of solution purges the H2S with it. If you smell a bit of stink during primary fermentation, keep an eye (nostril) on it, and it may disperse by bottling time.

Air it out

If your wine is still stinky on bottling day it can sometimes be cured by aeration, like the treatment for small amounts of excess sulfite. First, double-check the sulfite levels of the wine, and ensure they’re at least at the manufacturer’s upper limit. This is important since the air introduced will cause an oxidation reaction, diminishing the free sulfite, and if the levels are too low, the wine will be oxidized and your problem will be worse. Follow the steps described in aeration for excess sulfite.

Come and get me, copper

If it’s worse than a whiff, the fix used to be to treat the wine with copper, by tossing a handful of sanitized pennies in the carboy. Nowadays pennies are made of zinc or plastic, so better results come from gently stirring the wine with a clean, sanitized piece of copper tubing, the type intended for potable water plumbing. The H2S will react with the copper turning it into an insoluble copper sulfide. If you’re feeling especially clever you can form the copper tubing into a racking cane and in one quick rack take care of the problem.

Hold the sulfate, call the Germans

The standard treatment for high levels of H2S has long been treatment with a combination of ascorbic acid and a product called Cufex, which is a copper sulfate compound. The problem with this treatment is that even in quite small amounts, copper is toxic to humans (treating with elemental copper, like the copper pipe treatment described above won’t leave any harmful traces). Proper use of copper sulfate requires laboratory testing and measurements for safety.

Fortunately for us, there is a fairly new treatment available that is both easy and safe. It is a product called “Bocksin,” which is made by the German firm ERBSLÖH GEISENHEIM. Related to the fining agent silicon dioxide (Kieselsol), this product is stirred into the wine at a rate of one ounce per 6 gallons (30 mL per 23 L). It immediately bonds to the hydrogen sulfide 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. It may be necessary to rack and/or filter the wine after using Bocksin, but in most cases it seems to work like a late-night infomercial product, salvaging seemingly doomed-to-stinkiness wines with rapid ease.

Great Scott!

There’s another product now being used to treat excess H2S. Reduless is a product available from Scott Laboratories. It’s a combination of bentonite, inactivated yeast nutrient derivatives and is high in natural sources of copper. When used as directed (10-15 grams per 100 litres) it’s very safe and can de-stinkify a wine in as little as three days.

Know when to give up

There will come a point where the hydrogen sulfide will chemically change to another class of compounds called mercaptans, which have a range of odors including garlic, cabbage, onion, rubber, and skunk. Mercaptans are the same compound that is added to propane and natural gas to give it the distinct aroma that alerts people to gas leaks. Once it has settled into a wine there is no treatment.

Wine smells like yeast or bread

Actively fermenting wine will have a faint yeast smell, but if the wine in the carboy takes on a heavy smell like bread, or in some cases soda crackers or even brewer’s yeast, you may be smelling the beginning of autolysis.

Autolysis happens when inactive yeast cells disintegrate and release their internal contents into the wine. Essentially, the dead yeast rots and decomposes. Because the material they release is rich in amino acids, it has a distinctive odor. The good news is that autolysis takes many months to occur at room temperature, and even longer at cool temperatures, and in any case only happens in the presence of visible yeast sediment.

If you follow the instructions in the kit with regards to racking, fining and stabilizing you should never see autolysis in any of your wines. But if you miss racking a kit for an extended period of time, your wine may be vulnerable. If caught at the first sign, quick racking and sulfiting can prevent the autolysis from overwhelming the wine, but if it has already progressed to the point where it can be strongly detected as a brewer’s yeast smell there is no cure. In addition, because of all the amino acids in suspension, the wine will be far more susceptible to infection by spoilage organisms.

Vinegar smell

Your wine is infected with acetobacter, which are producing detectable amounts of volatile acidity (VA). In detectable amounts, this is pretty much another non-recoverable situation. Fortunately it’s very rare in wine kits, as it requires the introduction of acetobacteria (possibly courtesy of the winemaker’s mortal enemy, Drosophila melanogaster, the fruit fly) along with a lot of oxygen. Prevent it by excluding fruit flies, making your sulfite additions, and topping up carboys/filling airlocks.

From salad dressing to nail polish

In extreme cases over an extended time, VA can produce ethyl acetate, a compound that’s a dead ringer for nail-polish remover. While rare in kit wines, it is terminal. Sewer time for the wine, and follow the steps for excluding VA in the future.

Dead trout/rotting geraniums

Just as lovely as it sounds, this problem is unfortunately not as uncommon as we’d like to see in wine kits. When it is full-fledged, this condition can wrinkle noses at 100 yards, and once smelled is never forgotten.

The cause of this odor is 2,3 ethoxy, 3,4 hexadiene. It is produced when lactic bacteria consume the sorbate in the wine kit. These bacteria are present wherever human beings live, and are on virtually all surfaces and in the air. They are easily suppressed by the sulfite included in a wine kit. However, if the sulfite level falls, either through oxidation, or because the winemaker did not add the correct amount, they can infect the wine.

Normally lactic bacteria will produce low levels of off-odors, sometimes described as cheesy, mousy or musty. Most people will never notice them. However, in the presence of sorbate they produce the stunning aroma of fermented trout and flowers. This is a terminal condition, and the wine must be discarded.

The best way to prevent this is to make sure you are adding the full amount of sulfite included in the kit. If you are adding extra rackings to the processing of the kit, or if you are storing the wine for long periods of time, make sure to top up your carboys and monitor your sulfite levels.

Wine is stinky when poured

Bottle stink

When young wines are put into the bottle they sometimes carry a residual aroma of fermentation with them, often a hint of hydrogen sulfide or a slight yeasty character. This usually dissipates with time, but if you’re drinking your wine young, decanting it before serving or swirling it in the glass will often drive off most of the aroma.

If the stinkiness persists, your wine may have hydrogen sulfide or excess sulfite (see earlier). Also, make sure your wine is completely de-gassed before bottling. This will cut down on any off aromas carried into the bottle.

Mighty mousey

If some of your bottles of wine have an aroma like a wet mouse, or maybe a musty character, but others seem normal, you may have a tyrene or 2,4,6 trichloro anisole (TCA) contamination from your corks. TCA is a combination of a mold from the lignin, or fibrous part of the cork and chlorine, used in bleaching and sanitizing the corks after harvest. It’s a small but persistent problem in the cork industry, and one all winemakers have to live with, even if they use the highest quality natural corks. The cure for this is to switch to synthetic corks, which despite having some other challenges, never have TCA contamination.

The sunny side of the street

The good news in all of this is that most of these problems are actually very rare. Of the hundreds of thousands of wine kits sold every year, we see very few cases of real defects in processing. It turns out that winemakers are usually pretty savvy!

With good sanitation, accurate measurements of temperature and gravity, and detailed record keeping you should never see most of these problems. But if you do, again, don’t panic: Most of the common conditions are easily fixed.