We try to get ideas for newsletter features from the questions we are asked most often during wine tastings, and one such question is ‘what is corked wine’? Starting with that and moving on to another of the common faults, oxidation, here is a short guide. Whole textbooks have been written about these faults, so not everything is covered here – if you are interested in wine tasting and/or doing your WSET wine qualifications, and therefore need to know about wine faults, there is plenty out there for you to digest – drop us a line if you want to know more.
On a more basic level, understanding a little about faults and what causes them often helps people send back a faulty wine in a restaurant, for example, when maybe previously they would not have been sure and persevered anyway. Remember – life is too short to drink faulty wine!
1. Cork taint (aka corked wine)
In the vast majority of cases, it is the cork that causes this fault, but it’s not ‘bits of floating cork’ (although that can be annoying). The culprit is in fact a chemical compound called TCA (2, 4, 6 trichloro-anisole for those interested) which finds its way into the cork, either by the use of chlorine for bleaching corks, or from the tree (the cork oak, quercus suber) itself taking up pesticide residues from the soil, which then react with natural fungi. Other causes of cork taint are treated wood in wine storage areas (beams, walls or barrels), or simply a mould forming around an ill-fitting cork.
Human sensitivity to TCA is high (we can detect one billionth of a gram per litre), which partly explains why it is the most common fault we come across. Developments in cork hygiene and sterilisation have helped a lot, but the problem is still there, with maybe 1 in 40 bottles affected, although estimates vary a lot.
Normally it is quite easy to detect a corked wine; the first things that hits you is a mouldy smell reminiscent of a damp cellar (at least that is how I picture it), followed by a dry taste that lacks fruit and length. Of course, it is not always that obvious, but for me if the smell is even slightly mouldy, the taste is dry, and the fruit has gone missing, I’d consider it corked. In less obvious cases, my rule of thumb is that of you have to try really hard to find fruit and pleasure in the wine, both smell and taste, it’s likely to be a faulty wine.
Oxidation is a more complex. Generally speaking, wine needs oxygen, but not too much, and only at the right times. However, for fortified wines like sherry, Banyuls, Madeira etc, high levels of oxidisation are desirable. For this short guide we’ll stick to standard dry wines and define oxidation as ‘an excess of oxygen’.
Oxidation can occur from the moment the grapes are picked right through to storage of the wine in bottle, and for a variety of reasons, but with one common factor; the wine quality is permanently affected. If the oxidation occurs early in the winemaking, it is often not detectable until much later, so the only answer from the winemaker’s point of view is diligence at all times.
In the case of white wine, starting with the harvest, it is vital that only healthy grapes are picked, preferably by hand. Then, the grapes should be gently pressed and transferred into the fermentation tank as soon as possible, at cool temperatures. Finally, during the period between harvest and the start of the fermentation (about 48 hrs, normally) the juice should be protected from oxygen by use of an inert gas such as carbon dioxide, or dry ice. During the fermentation the wine is protected by the natural production of carbon dioxide, but after fermentation and before bottling, there is always a risk any time the wine is moved, say from one tank to another, or tank into barrel. At this stage the wine should be warmed slightly as oxygen dissolves into wine at a higher rate when the wine is colder. Thereafter, storage tanks or barrels should be perfectly full, clean and airtight, allowing for a controlled dose of oxygen from time to time to prevent reduction (another fault, kind of the opposite of oxidation).
For red wine, the same basic rules apply, with more emphasis on the storage after fermentation as red wine normally spends a lot longer in tank or barrel before bottling, increasing the risks of a slow oxidation. Particular attention should be paid during the few weeks before a bottling, when temperature, sulphite levels, and cleanliness of material such as pumps and pipes have to be rigorously maintained as the wine is moved around in preparation.
Furthermore, growing conditions even before harvest can have an effect; if the vines are stressed during the growing season (say in a drought year), they may not contain enough natural compounds that protect from oxidation later. Higher-yielding clones of certain grape varieties may also lack these compounds (called phenolics), so vine quality is a factor.
After bottling, a poor quality cork can allow oxygen in, despite any efforts made in the vineyard and winemaking. This is the responsibility of the winemaker and their cork supplier, to ensure the corks are good enough. Here at Chollet, for the white and rosé we use nomacorc ‘green line’ recyclable corks which are pretty much guaranteed problem-free, and for the reds we use good quality 49mm real corks, again to minimise any potential issues.
Nomacorc Decent, blemish-free corks are important
Whatever the cause, an oxidised wine tends to lose its clarity, and sometimes go cloudy. The colour takes on a brownish tinge, smell slightly of rotten fruit (oxidised apples, for example) and taste flat, burnt, or nutty.
Both of these faults can affect both red, white and rosé wines, but it’s white wines that suffer the most, with more delicate flavours. For example, for a number of years many Burgundy white wines suffered from premature oxidation, even top end ones. The causes are still being debated, although it’s likely to be a combination of all the above, plus the fact that Burgundy white is aged in barrel for longer than most other whites. Things are a lot better now, but oxidation can never be controlled 100%. So, remember – if you believe a wine is corked or oxidised, it probably is – and don’t be scared to return it.
Happy tasting! (the 99% of wines which are perfect, anyhow!)
Oxidised wine (picture credit; the excellent Wine Folly)