Ever wondered why a wine bottle has a dimple on the bottom? Some people have suggested so the sommelier looks cool as he serves the wine! Certainly it has that function, a lucky secondary use.
Firstly a glob of molten glass is taken out of the furnace on a metal blow tube, the glass blob is then expanded and shaped with tools to the right shape. 600 to 800mls was a common volume for a glass blower to blow in one breath, this became standardised to 750 mls wth mechanisation and tighter regulations. Once the bottle was ready the neck needed to be formed so a pontil rod was temporally attached to the base with a small extra glob of molten glass. Once the top was formed this union was not needed so was broken. This left a jagged piece of glass. To stop this scratching the surface it was on and to made the bottle more stable this was then inverted into the bottle to form the punt.
This was a fontunate development with regards to sparkling wine and cider. It was soon discovered that both could stored safety in these new glass bottles developed by Digby in England. The punt adding extra strength to the bottle to withstand the pressure. The pressure is significant a nutmeg of sugar as recommended by Worlidge in 1680 would produce about 6 atmospheres of tree times the pressure in a car tire. The punt acting like an arch. Romans discovered that an arch bridge withstand weight better than a flat one millenia ago. Also increases the ratio of glass to contents.
With whats now called method ancestral, ie. in bottle fermentation without disgorging, The moat around the punt caught the lees and made pouring a clear glass of cider easier.
The punt provided a grip for manual riddling prior to disgorging if required
Marketeers saw advantage the punt makes the volume of the bottle smaller!
Probably for the latter, the punt remains on most wine bottles long past its need with modern injection moulds. A bottle with a punt also in perceived as containing superior product! even champagne makers have long resisted the need to reduce the carbon footprint now available with modern glass technology too thin the glass and reduce the size of the punt, fearful of public perception.
At TeePee Cider we use tradition 880 gram thick green 'champagne' bottles for our traditional cider, as a hat tip to Kenelm Digby