Look on the bottom of a
bottle of
wine; the indentation you see is called a
punt.
Why is the punt there and what purpose does it serve? alt.food.wine has been asked this many, many times and lists among the most popular answers:
1. An artifact of the bottle making process. When bottles were hand-blown, the hot bottle was transferred off of the blow pipe onto a device called a punty in order to cool. This device caused the indentation to appear in the finished bottle, and so it has remained a part of bottle design.
2. A way to make the bottle stand up better. A flat-bottom bottle design would have very little room for manufacturing error. A concave bottom design would not suffer this problem.
3. To strengthen the bottle and prevent the bottom from blowing out. This is the most common explanation; however, (according to alt.food.wine) there is little evidence to support this -- and at this time no one has bothered to do the maths required to confirm or deny this. You might notice that champagne bottles have the largest punt of all wine bottles, supposedly to withstand the pressure created by the sparkling white wine -- so whether or not this is the right explanation, the wine makers certainly seem to put some stock in it.
4. It has remained part of the design for several practical reasons: It makes the bottles more stackable, it creates a place for sediment to collect, and it allows the bottle to be more easily (and some say more elegantly) gripped from the bottom for pouring. These might all be true, but they are certainly all afterthoughts and probably not original design considerations.
5. It makes the wine more esthetically pleasing/marketable. Ouroboros astutely suggests that the punt takes up just enough space so that the bottle must be made taller, and thus will stand out above other bottles on a shelf.
This node was made possible by the Vintage Voice alt.food.wine Punt FAQ