U is for Ullage, Uvula, U Know

U is for ullage, uvula, U know, it’s one of those weird U words. But in wine it serves a purpose.

Ullage is the small space of air in the bottle between the top of the wine and the bottom of the cork. This space is provided to allow for any expansion of the liquid during storage. As wine ages this space—the ullage—grows because the wine is evaporating slowly through the cork.

For centuries corks have been made from the wood of the—wait for it!—cork tree, which is a majestic evergreen oak native to the Mediterranean region. Fifty percent of the world’s cork is grown in Portugal alone. Like grapes, cork is harvested, in this case from a mature tree, which means the tree is not chopped down but rather layers of the living tree’s trunk bark are cut away to be fashioned into cork wine stoppers. One oak tree can be harvested a dozen or so times during its lifetime.

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But with corked bottles, the ullage grows because precious wine—albeit just a little each year—is being lost. It's the 21st century, isn’t there a better way to seal bottles?

Enter the lowly twist off cap. Wine consumption continues to grow worldwide with China being the latest region to embrace the "nectar of the gods". Making wine for China's billions of people, as well as the rest of the world, has meant that demand for cork far exceeds supply. In response the past 15 years have seen a rise in the number of vineyards opting to seal their bottles with twist off caps.

Some of the first adopters of the twisties were white wine makers. Once opened white wine has a longer shelf life than red wine and if re-capped and stored in the refrigerator, can be drunk up to a week or more after opening. Once opened every bottle of wine is exposed to oxygen, at first this aeration will enhance the wine's flavor. However if the bottle is not consumed at one sitting and is re-corked with its cork wine stopper, the oxygen will continue to work on the wine through the permeable cork. Using a metal cap decreases the changes in flavor caused by aeration over time thus allowing white wines to be drunk over a number of days.

Nevertheless, some people dislike the taste of wines with a metal twistie and prefer wines sealed with cork.

It may be humble but a twist off cap also means the ullage doesn't grow during storage, which means more wine for you and all those billions of Chinese wine fans.

So the debate over which is better—cork vs. twist off—is irrelevant. Winemakers choose the best sealant option for their wines and business. So it's not cork or twistie, it's cork and twistie.

And that's what really matters: getting the best bottle of wine U can, U know?