Why is there an indentation in the bottom of a wine bottle?

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Dear Dr. Vinny,
Why is there an indentation in the bottom of a wine bottle? This is deeper in some bottles than in others.
—Bob C., Ashland, Ore.
Dear Bob,
That indentation is called a punt, and it’s a good thing that football season is over, or I would be trying to make a joke about the name. Historically, punts were a function of wine bottles being made by glassblowers. The seam was pushed up to make sure the bottle could stand upright and there wasn’t a sharp point of glass on the bottom. It’s also thought that the punt added to the bottle’s structural integrity.
Bottles nowadays are much stronger and machine-made, so the punt is simply part of wine-bottle tradition, though some say it helps collect the sediment as wines age. Punts no longer serve a structural function except in bottles of sparkling wine, which have constant pressure inside. In these cases, the punt allows for more even distribution of pressure.
The size of the punt doesn’t mean anything about the quality of the wine inside, but it can be a bit gimmicky, because some bottles just look like they’re on steroids, with deep punts and extra-heavy glass.
—Dr. Vinny