Why do some wine bottles have indented bottoms?

Cecil replies:

The indented bottom, called a punt, is useful in the traditional method of making sparkling wines, known as riddling or remuage. The bottles are placed in special racks with the top of one nestled into the punt of the next, then gradually tipped upside down. This causes sediment to settle into the neck of the bottle, from which it’s eventually removed. In still (nonsparkling) wines, the punt serves the same purpose as the indented bottoms of tavern beer steins–it makes you think you’re getting a lot more than you are.

Cecil Adams

Send questions to Cecil via cecil@straightdope.com.