For the wine amateur and wine enthusiast who wants to know at the wine producer level how foul odors can get into wine, we found a great article courtesy of Brabant Wine Brewers.
Foul odors usually arise from a major fault, a degeneration or a contamination. Emergence can occur at any step of vinification due to:
- insufficiently ripened fruit
- failure to control alcoholic fermentation
- insufficient control of aeration during lagering
- An incorrect dosage of potassium disulfite (CDB)
Sometimes neglect, insufficient care or ignorance lead to severe consequences. These can be not only odor and taste abnormalities, but sometimes the wine can become unpalatable or even toxic.
The 12 major faults of wine
(Origin Description: Responsible molecule)
Grape harvest:
1. Vegetal: Trans-2-hexenal
Oxygen:
2. Overripe apple: Acetaldehyde
3. Vinegar sting: acetic acid
4. Glue (varnish): Ethyl acetate
5. Soap: Decanoic acid
Sulfur:
6. Sulfur: SO2
7. Rotten eggs: H2S
8. Onion: Ethaanthiol or Mercaptan
9. Cauliflower: Dimethyl sulfide
Phenols:
10. Horse stable: Ethyl-4-phenol
Mushroom:
11. Moldy soil: 2-ethyl-phenchol
12. Cork taste: trichloroanisole, TCA
1. Vegetal
After pressing the grape, the press cake will take on a grassy character. Sometimes it happens that, even after fermentation, these odors of leaves and/or crushed zests pass into the wine. The cause can be sought in:
- the use of unripe fruit
- inadequate deodorization
- overpressure during pressing
Trans-2-hexenal is formed by enzymatic oxidation during transport and handling of the grape harvest¬. Above 0.5 g/liter, this substance causes grassy odors and flavors. This error can be prevented by very brief contact of the rists with the must.
Oxidative odors
It can happen that wine, when in contact with air, does not become acidic but oxidizes: this can be due to the action of enzymes or microorganisms. All wines then taste the same, their own fruit aromas disappear. If the air contact is short then the fruity aroma can fully return after moderate addition of CDB. If there is prolonged aeration, then depending on the acidity, the damage will be permanent (see 2, overripe apple).
- After an operation such as siphoning, filtering or transport, the wine may be so-called "tired": less aroma and less fine fruit notes. With sufficient rest, everything returns to normal.
- Is the treatment more intensive, with more aeration, such as brutal over-pumping or improperly executed bottle filling, the wine takes on the flavor of "bruised" fruit, fruit that has been left after bruising.
- An "aerated" wine has absorbed even more air and usually still partially evaporated. After several days, it gets worse.
- "Oxidized" wine is one step further and the air-induced damage is practically impossible to repair ( see 2, overripe apples).
- "Made-up" wines result from prolonged air contact. White wines turn dark yellow and red wines turn brown, they lose their freshness and fruitiness, they become bitter and acquire the taste of overripe apples (see 2).
- "Oxidation" is sometimes desired as with: Banyuls, Porto, Xeres, Madeira and Marsala, these are the so-called Southern wines. Above 16 vol% alcohol, spoilage is no longer possible. By exposure to varying temperatures after a longer period of time, the wine acquires the "Rancio" aroma of dry nuts and apples. This wine no longer loses its individuality, even in a partially filled bottle.
2. Overripe apples
If the wine was not protected from oxygen, one gets excessive formation of acetaldehyde. The smell of overripe apples and nuts overpower the primary fruit aromas and secondary fermentation aromas. It is the familiar musty smell.
Become young and lightly alcoholized wine in contact with air for a long time then a thin membrane will appear on the surface. That film consists of a fungus that is everywhere in wine cellars. It is the "Mycoderma Candida," this fungus will oxidize the alcohol to acetic acid and acetaldehyde. This contamination can be stopped by reducing the contact area: fill bottles to the neck, add enough CDB, remove the membrane and carefully pour 70 vol% alcohol. Not only does acetaldehyde bring the smell of overripe apples, it also causes headaches.
3. Vinegar sting
Vinegar sting is caused by the acetic acid bacteria Gluconobacter and Acetobacter. One then finds in the wine an excess of acetic acid ethyl acetate (the compound of ethyl alcohol and acetic acid). This requires air contact. In normal wine one finds 200- 300 mg acetic acid and 60- 80 mg ethyl acetate/liter. Above 700- 800 mg/1 acetic acid and at 150- 180 mg/1 ethyl acetate, the wine is already suspect. At this dose, acetic acid still has its specific aroma, but also develops sharp edges.
Ethyl acetate on the other hand has an aggressive odor with sharp burning taste. Ethyl acetate causes the degradation of the wine's fresh cleanliness, much more than acetic acid itself.
Volatile acids intensify the unpleasant impression of the solid acids and of an excess of tannin, this can be disguised by an excess of alcohol or sugar. Refilling the wooden barrels, sometimes twice a week, is necessary and prevents the formation of acetic acid. Much depends on temperature, pH and sulfite content. All wines contain acetic acid; it is even believed that acetic acid contributes to the aroma profile. An excess of this acid is a wine fault and causes a harsh pungent taste.
Vinegar sting is a serious, unrecoverable wine fault. Only precautions make sense, one must:
- keeping the wine material in a perfect state of purity
- take great care in vinification, pursue sufficient acidity and avoid volatile acids
- Avoid all air contact during lagering and storage
- Always use the correct amount of CDB
4. Glue (varnish)
In the wine, the acetic acid formed will react with ethyl alcohol and form ethyl acetate. This product is the cause of the odor of glue (varnish). A reduction in alcohol volume% and an increase in volatile acids then follows.
Increasing risk`s for the formation of ethyl acetate:
- wine with low alcohol by volume%, with lower acidity and more volatile acids
- longer contact of the wine with the air surface
- poor cleaning of the wine equipment
- Wines with more than 0.88 g/l of volatile acids for white wine and more than 0.98 g/l for red wine are destined for vinegar manufacture or distillation.
If the volatile acid is below this dose, the wine is still enjoyable, but further ethyl acetate formation must be prevented. This can be done by:
- addition of CDB : 0.3- 0.5 g/10 liter, followed by clarification or filtration
- or by heating the wine to 70o C (pasteurization), letting it cool for 2 hours and bringing it back to 70o C and letting it cool down
5. Soap
During fermentation, yeast can form fatty acids and after lagering, they can form soap. In young white wines, this soap odor can occur. The higher the alcohol content the more soap smell.
Reductive odors
Reduction is the opposite of oxidation. Influence of air is the cause of oxidation in wine. Wines that were either aerated too late or too little during vinification can develop reducing flavors, especially red wines, especially if the grape is of Spanish, Italian or Greek origin. This type of wine should always be siphoned twice after fermentation with plumping. It is also normal, before drinking, to pour the wine into a decanter so that the most volatile sulfur compounds can escape and evaporate.
If the reduction ma the fermentation continues, then there may:
- Due to an excess of CDB or SO2 a sulfur odor occurs
- hydrogen sulfide or H2S occur, with the smell of rotten eggs or garlic
- After combining alcohol with hydrogen sulfide, mercaptans are formed, with odors like onion, groundnut, gummi
- Further di sulfide can also be formed, this odor then resembles cooked asparagus or cooked cauliflower. Light can give white wine stored in colorless bottles a light taste.
6. Sulfur Flower
If the sulfurization was done poorly, sulfur odor can occur with too much CDB or SO2. Nevertheless, adding CDB is extremely important:
- This inhibits the development of wild, unwanted yeasts
- It prevents the development of acetic acid bacteria
- It ensures preservation in ideal conditions for the wine
- It prevents oxidation and stabilizes the color
- it can, after bottling, prevent secondary fermentation in the bottle
The dose should be sufficient to obtain the above effects. Do not use too little in white wine or it may oxidize.
7. Rotten eggs
When an egg decomposes, sulfur-containing proteins will develop hydrogen sulfide. The same gas develops when CDB is overdosed in fermenting wine. As mentioned above, H2S is the precursor to a whole range of sulfur compounds that are very unpleasant for wine, to say the least.
8. Onions
If sufficient H2S is present, it will bind with the alcohol. This substance formed "mercaptan" has a very low odor threshold: 1 part in 10,000,000 is already observed.
The odor can be compared to that of onions. Less than 0.7 mg/l is already detected in wine. In alcohol of 40 volume% this error seems even worse. Mercaptan can be removed by aeration and siphoning. Also introducing a piece of copper metal into the wine can precipitate mercaptan.
9. Cauliflower
Dimethylsufide (DMS) is quickly smelled upon opening the bottle (0.33 ug/l). The cause is often insufficient pre-clearance before fermentation. There is no remedy for this.
10. Horse stable or horse manure
Certain phenols, which are natural substances, can produce odors reminiscent of:
vanilla, woody, clove or carnation or animalic. The main derivative is ethyl-4-phenol in red wine. This is always formed by yeasts of the species brettanomyces (gueuze yeast). Ethyl-4-phenol can also be formed by lacto-bacilli and lactic acid bacilli. 2 mg/1 has an odor of leather and 4 mg/l has an odor of horse manure (tasty is different). Prevention is possible by adding enough CDB. Curing cannot!
11. Damp musty earth
These odors usually occur due to a lack of hygiene of the barrels, vats and other wine equipment. Usually microorganisms are at the root in the wooden barrels. Cleaning and disinfection are of utmost importance here. For most winemakers, especially beginners, using wooden barrels causes more discomfort and disillusionment than benefits.
The wooden barrel must always be kept full either with wine or water. Clean with special chain or pressure washer and then steam.
12. Cork flavor
Cork was the only sealing agent for the wine bottle until 40 years ago. Cork is chemically inert, stable, seals air and wine tight, elastically compressible. And yet 2 to 5% of corks have a "cork taste." There are several possibilities:
- The rotten smell (buttery) coming from cork harvested from the base of the cork oak trunk, if it has yellow spots (rare, 1 in 100,000)
- Taste and smell of sewage from poor drying or poor hygiene during cork treatment
- Odor of solvents and smoke (guajacol), when a cork is leaking, thus breeding fungi and bacteria on the bottle. These are also on the inside of the bottle
- The musty "cork smell" in 80% of bad corks is caused by the use of chlorine derivatives in washing the corks. Trichloroanisole (TCA) is then formed. A minimal amount is already observed: 1g in 1,000,000,000 l, it contaminates the cork and the wine. If in the wine cellar wood was treated with chlorinated products, TCA can contaminate all wine bottles in the cellar. The latter is then called false TCA contamination.
Source: Brabantsewijnbrouwers.nl
