Sitting in a restaurant with crisp tablecloths and sparkling glassware it’s easy to forget that wine is a natural product, created from grapes by the actions of microbes. Microbes aren’t completely controllable, plus things can happen to the grapes while they’re growing or during harvest, which can affect how the wine tastes. But as I discuss here not all these changes are negative, it is often a question of degree, and as always with wine personal taste plays a role.
Cork taint
Poor old corks are much maligned, and ‘corked’ gets used as a cover all expression for almost any wine fault. Corks are traditionally made from the bark of the cork oak, which if contaminated, can impart a musty smell to the wine. The chief chemical compound responsible is trichloroanisole, TCA for short, and humans are incredibly sensitive to it. It comes from fungi present in the cork bark, and despite many attempts to eradicate it, it’s still with us. The incidence has gone down, partly because producers are being more careful, and partly because many wines are now sealed with alternative closures, but the rate is estimated to be around 1% of bottles. At high levels you get a really nasty whiff of damp cardboard. At lower levels it diminishes the fruit characters the wine might have been expected to show and can go unnoticed.
Brettanomyces
This is the name of a yeast that can sometimes grow in wine after the regular alcohol-producing yeasts have done their job. It usually only occurs in red wines, which offer the right sort of substrates and the right level of pH for brett (as it is often referred to) to flourish. Brett can lurk in the winery, in barrels, and can originate in vineyard soils and come in on the grapes, it flourishes when winemaking isn’t attentive enough. It creates distinctive savoury, smoky or leathery characters in the wine. As well as slightly animal (some describe it as barnyard) and phenolic (think Germolene or fabric sticking plasters) aromas.
Brett is an example of a ‘fault’ that for some is to be rejected whereas other people quite like it. It’s a question of context, degree, and personal tolerance.
Reduction
The term reduction refers to the presence of a range of volatile sulfur compounds in wine, which are produced by yeasts during fermentation. They include: hydrogen sulfide, which smells of cooked eggs, blocked drains and farts; disulfides, thioesters and thiols (also known as mercaptans). Often hydrogen sulfide gas is produced early during fermentation and disperses. If it doesn’t and is converted into other compounds, then ‘reduced’ characters can stick around in the wine. They are variously described as smelling of cabbage, rubber, eggs, cooked corn, onions and gunflint. Some reduction can be a good thing, and a lot of winemakers like to toy with it in Chardonnay, where the minerally struck match/flint character can be very desirable. And some thiols give appealing passionfruit and grapefruit aromas, too. So reduction is another character that isn’t necessarily a fault in the right setting and at the right level.
Oxidation and Volatile Acidity
These two often come together. Oxygen is desirable during fermentation because yeast is a living organism and needs to breathe. Afterwards small amounts of oxygen, such as the micro oxygenation delivered through ageing in barrels, allow the wine to develop in favourable ways. But later on – at bottling and beyond – oxygen is the enemy, reacting with the wine to deaden fruit aromas and making the wine taste overly dry, stale, nutty and earthy, or in whites like bruised apple. The colour also changes: reds go brick red and then brown; whites get darker, gold/bronze and eventually brown too. For some wines oxidation is part of the style. Think Madeira, Tawny Port, Oloroso Sherry, old-school Rioja or Banyuls. And of course limited oxidation plays a role in wine ageing.
Volatile acidity is caused by acetic acid bacteria, yeasts and other bacteria normally present in wine. At low levels it can be quite nice, giving fruity aromas often described as ‘lifted’. If the bacteria are present, and the wine sees too much oxygen, then the levels can become problematic: resulting in distinctly vinegary aromas from acetic acid; sometimes together with the smell of nail polish remover from ethyl acetate.
Mouse taint
As natural wines become more widely known and sold there has been more discussion of a fault called mousiness (goût de souris in French). Sometimes found in wines made without any protective sulfites, and named as it manifests as the smell of mouse cages and biscuits. It only emerges when the wine is in your mouth, your saliva raises the pH, and the stinky compounds are liberated. The difficulty with mousiness is that some people aren’t sensitive to it, but once you’ve spotted it, assuming you can, it makes the wine undrinkable – eek!
When a flaw isn’t a fault
When you begin to learn about wine faults and develop some confidence in detecting them, there is a temptation to become the fault police, calling out even the smallest traces of a flaw. But it’s not that simple. As we’ve seen the presence of small levels of some flaws can add interest to a wine. The Japanese have a concept called wabi sabi. In this idea, small flaws can accentuate or bring out beauty, so perfection is not simply the absence of any flaws.
There are clearly a number of things that can go wrong during winemaking. But it’s a complicated subject, and it’s not black and white. Sometimes the presence of a particular concentration of a ‘fault compound’ in one wine can be a positive, while in another it can ruin the wine. This complexity can be daunting, but it’s all part of the fun of wine. After all, we wouldn’t want to be drinking soulless, processed techno wines, which is what we’d have if all ‘faults’ were ironed out.