Bottle variation is a wine word. It is not a word that is particularly positive.
Do you know what it means? And what are the main causes of bottle variation?
Bottle variation in wine means that bottles of the same wine smell and taste differently. It is essentially a wine fault.
Bottle variation is not to be confused with vintage variation, which is not a fault. Vintage variation is a reflection of two different growing seasons climatically.
A few weeks ago I opened a bottle of 2007 Bandol. At $40 it was not an inexpensive bottle. The wine tasted tired, slightly oxidized and dried out. To put it mildly I was a tad disappointed. A week later I opened a second bottle of the same wine (bought from the same retail store on the same day). It was as fresh as a daisy, packed with delicious flavors, lively and a joy to drink. If I just bought one bottle I might have firmly decided that I:
- Did not like this producer or worse
- Did not like any wine from Bandol – period!
The problem was not the wine (per se) or the producer but bottle variation.
Causes of Bottle Variation
There are a number of causes of bottle variation in wine. But most causes essentially relate back to:
- Variable levels of oxygen exposure, or more particularly variable Oxygen Transmission Rates (OTRs)
- Closure taint
- Too little or no use of sulfur dioxide
- Temperature spikes and temperature variation during transportation and/or cellaring.
Variable Oxygen and OTRs
Variable OTRs occur when a wine is closed with a cork stopper. Cork is a natural product. As such each and every cork is unique and allows variable rates of oxygen transmission through the cork to the wine.
Oxygen is both a friend and a foe of wine. A certain amount is desired (even needed) to help a wine gracefully integrate, evolve and develop its complex bouquet. But too much too quickly can destroy a wine, rendering it prematurely ‘over the hill’. The longer a wine is aged in bottle the more discernible the effects of variable OTRs.
While winemakers can measure and control the levels of dissolved oxygen in wines before and at bottling, they cannot measure or determine the amount of oxygen already trapped inside the tissue of each cork, or the rate at which oxygen will pass through the cork to the wine during cellaring.
Additionally, not all wine closures seal out oxygen ingress equally well. This is not a problem exclusive to natural cork. It can also be a problem with plastic/synthetic or technical corks leading to what is termed ‘premature oxidation’.
Problems with wines caused by cork taint have been well documented. Even with wines bottled at the same time, some may have tainted (TCA infected) corks and others not. See my previous post on cork taint for more detail on cork taint.
Too Low Levels of Sulfur Dioxide
One of the key properties of sulfur dioxide (SO2) is being an anti-oxidant. As explained in a previous post ‘SO2 plays a very important role in maintaining a wine's freshness’ and minimizing destruction from unwanted or excess oxygen exposure.
Temperature spikes and/or significant temperature variation during wine transportation or cellaring can also cause bottle variation. Wines dislike sudden heat spikes or sudden temperature shifts, preferring a moderate constant temperature. If a wine is exposed to a very warm environment, it evolves too quickly; the fruit fades and the wine takes on a tired, baked character. Heat-affected wines taste over-the-hill, dull and past their peak.
While a lot of bottle variation in wine is caused by some post bottling ‘event’, some bottle variation problems relate back to the bottling process itself. If the same wine is bottled at different times, it can lead to variation in taste. Similarly, if the levels of dissolved gases in wine (notably oxygen) are not measured and controlled, bottle variation is more likely.
Reducing the Incidence of Bottle Variation
Today, bottle variation and its causes are much better understood than in the past. While it is still more of an issue with older wines that have undergone extended bottle age, it can also be found in relatively young wines. Winemakers, duly concerned about it and the negative impact that bottle variation can have on their reputation, continue to invest in improved QA/QC systems to reduce the incidence of bottle variation.