Top 6 Wine Faults: Their Causes & How to Identify them?
- Cork taint / TCA
What is TCA?
Trichloroanisole or TCA is a natural compound most generally found in wood that has been in contact with some form of chloride chemical.
When Chlorophenols found in certain pesticides and wood preservatives, get in contact with wood, they can be transformed by fungi into TCA and other bad smelling molecules. Because most of the wood surrounding us is treated with preservatives so it doesn’t rot, the contamination come from anywhere.
If a contaminated wood gets anywhere near wine, the bad odours concentrate into the wine until it may eventually become ‘tainted’.
Main source of TCA in wine is obviously the cork for 2 reasons:
A cork is essentially a piece of wood (or bark to be precise) that comes from a tree (the majority of cork trees used for making wine corks are grown in Portugal). If that tree has been in contact with chloride compounds at any given time in its life, its bark may have developed bad smells
A cork is obviously in close contact with wine allowing bad aromas to contaminate the liquid.
But TCA may also have contaminated the wine before it was even bottled if affected wood was present at the winery (in timber or pallets for example). TCA may even get from the outside into the wine through the cork if the bottle is stored in a TCA-rich environment (e.g. a contaminated cellar).
TCA can be eliminated. Take an apprx 18″ length of kitchen plastic wrap and roll it loosely into a tube. Insert into bottle, cork it (with plastic cork) and let stand for at least 24 hours. I use this method when corking happens to a wine that can’t be replaced and must be consumed for any number of reasons.
How to identify cork taint?
A strong smell of wet cardboard, wet newspaper, or intense mushroom odour is what you’re looking for.
In addition, if it really is TCA, all other aromas and flavors in the wine (fruit, oak, spices, etc.) should be difficult to smell and be hidden in the background.
Aged wine can develop some mushroom aromas that can be confused with TCA. How you can tell the difference is that without TCA, you should still smell many other flavors, spices in particular.
- Brettanomyces a.k.a. “Brett”
What is Brettanomyces?
Brettanomyces is a yeast of a different genus than the one we like that runs the alcoholic fermentation (Saccharomyces). Brett as it’s often nicknamed can grow in the wine and synthetize bad smelling compounds, volatile phenols to be precise.
Brettanomyces yeasts are virtually present in every wine. In fact, it has been found that they are already present on the grapes in the vineyards before they even make it to the winery. But most generally, their population in the wine remains too small for them to generate enough bad smelling molecules, so we don’t smell them.
Sulphur dioxide added to wine helps maintaining the Brett population at a low level. One of the reasons SO2 preservative is added to wines.
How to identify Brettanomyces?
No wonder why vinyl is often used to describe Brett’s odour. Some of the phenols responsible for the smell have a similar chemical structure to our good old disc records (vinyl-phenols).
Some paints contain volatile phenols as well so the smell can be associated with paints.
Wild game, horse sweat or stable are the most common descriptors.
What is Reduction?
Reduction is the opposite of oxidation.
With oxygen, wine oxidizes. Without oxygen, wine reduces.
Because wine is famously full of anti-oxidants, it tends to absorb all traces of oxygen. This is generally a good thing, with health benefits and a natural ability to sustain oxidation.
But during fermentation, yeasts actually like a little bit of oxygen. If they don’t have any at all because the winemaker doesn’t aerate the wine at all, yeasts compensate by transforming sulphur compounds naturally present in every food into bad smelling molecules.
How to identify reduction?
The bad-smelling compounds that form the reductive character of a wine, are the same as the ones found in eggs (especially rotten ones) or cabbages.
Smelly plastics like rubber or tires are also full of them. So that’s what reduction in wine smells like.
Fetid waters are also reductive media, so they develop an odour of reduction.
Tips to eliminate reduction?
Aerating the wine will oxidise the reductive compounds, making them odourless.
This can be achieved by opening the wine in advance, decanting it, pouring it out of the bottle and back in, or simply leaving it breathe in the glass for a while.
What are mercaptans?
Mercaptans are sulphur compounds like the ones described in the section about reduction, but that are bound with other molecules in the wine. This generally happens when a wine suffering from reduction has been bottled with all the reductive compounds in it, without prior aeration to solve the problem. The small sulphur molecules react with bigger aromatic compounds in the wine and bind with them.
How to identify mercaptans?
Because sulphur can bound with many different aromas in the wine, mercaptans can smell of many different sulphur-rich foods like cabbages, garlic or onion.
Drop a coin containing copper (the bronze-like ones, not the silver-like ones) in your wine glass and agitate for a minute. The coin will absorb the mercaptans, making all other flavors available for your nose to smell again.
- Volatile Acidity:
What is volatile acidity?
Volatile acidity (or V.A. as winemakers refer to it) is called this way because it is made of acids that can ‘fly’, that are volatile.
Most acids can’t ‘fly’ or can’t evaporate out of the liquid they’re into, even if warmed up or boiled. Volatile acids can.
Volatile acids primarily come from the oxidation of alcohol by bacteria. These acetic bacteria feed on the alcohol in wine, and transform it into vinegar.
Have you ever noticed that cooked vinegar (e.g. a vinegar reduction) is a lot less acidic than raw vinegar? That’s because the aggressive acid has evaporated out of it. Put your nose over a hot pan and through vinegar in it. You will feel the volatile acidity evaporating.
How to identify Volatile Acidity?
Essentially, vinegar is full of volatile acids so that’s what V.A. smells like.
A wine with high volatile acidity, is a wine that is on its way to turn into vinegar, its natural fate.
Nail varnish remover is full of acetate, a form of volatile acid. So it smells like some high V.A. wines.
What is oxidation?
When aromatic compounds get in contact with oxygen, their chemical structure is modified, changing their smell.
Oxygen typically gets in contact with the wine through the cork. It happens if the cork has some structural defects or dries up while the bottle is left standing. High temperatures accelerate oxidation hence storing wine in cool places is always better.
How to identify oxidation?
Oxidation converts normal wine aromas like fruit aromas into less enjoyable ones.
Oxidation generally translates into flavors of green apple, walnut or fennel.