Written by Nick Bulleid MW
In this edition of Ask the MW, Nick Bulleid MW looks into the ageing process of wines stored under screwcap compared to wines sealed with natural cork.
Cork allows oxygen to enter into a wine bottle and the amount varies from very high to low. This means that wines sealed with cork will age over time in a different manner from bottle to bottle. Do wines sealed with a screwcap allow oxygen into the bottle? Does this assist the ageing process or do screwcap wines retain their closed character?
You are quite correct that a cork closure allows a variable amount of oxygen to enter the bottle. (Occasionally, it’s variations in the bottle’s bore that allows the variability, but usually it’s the cork.) Screwcaps do allow oxygen in, too, but at a rate that’s much lower, and closer to the lowest transmission of “best” corks. Unlike cork, however, the rate differs little between bottles, provided the cap hasn’t been damaged. The consequence is that wines in screwcapped bottles develop at about the same rate as the freshest or slowest of the batch under cork.
However, there are many who believe that wine develops perfectly without oxygen, including Prof. Pascal Ribereau-Gayon at Bordeaux University, who has stated, “The evolution of a wine doesn’t require oxygen. The wine develops its own organoleptic capacity in a reductive environment where it acquires superior quality characteristics.”
I’m not sure what you mean by “closed character”, but there are distinct differences in the way wines age under the two closures. In my experience, whites retain more fresh fruit under screwcap, while still acquiring complex developed flavours. There’s less “toast” and also none of the slightly oak-like flavour that you get from the cork, commonly called “cork-wood”. I have not come across sporadic oxidation in screwcapped whites, this being the huge variation in development under cork, from “fresh” through “developed” to “oxidised” in the same carton. I think screwcaps are the perfect closure for whites.
With reds, the case is less clear as it depends on what you want from your wines. If you want to drink your reds with complex, developed flavours and not have to wait too long, then go for cork, but you had better be prepared for bottle variation, including some dullness and the odd oxidised bottle. If you want the most consistent aging and are prepared to wait, go for screwcap. The flavours will be fresher and more intense, but the complexity will also be there given time. With very big reds made for long ageing, the tannins may be a little tough at young age, depending on how the wine has been prepared for bottling.
Don’t be concerned about what you might read of reductive pongs under screwcap. The issue has been overstated and, besides, these are often present with cork, too.
When referring to “cork” I’ve meant natural cork. However, the new technical corks, made from fine fragments moulded together under pressure, seem to be excellent – more consistent than natural cork and almost entirely free of cork taint.
This is the full text of the article submitted. The published version may have been edited. Australian Wine Selectors January 2007.