Cork

Cork use to stopper bottles was increasingly used in the 17th C however it was the introduction of the corkscrew, first recorded in 1686 that accelerated its use. Before that it was not possible to tightly fit corks as they were difficult to remove!. An early device was used simply an awl but this often damaged the glass bottle neck and glass bottles initially were expensive.

Initially the cork was partially inserted and then tied down by pack-thread to the string lip. An invention of Sir Kenelm Digby. This persists in Champagne bottles

Corks were known to the Greeks and Romans. Pliny mentions them in his Natural History but fell from common use thereafter. Corks were mentioned by Sir Hugh Platt in his book of 1602 Delights for Lady  in the bottling of beer but probably was used with ceramic not glass bottles. Corks were also mentioned by Gervase Markham in his book English Hus-wife of 1602 saying “corks should be tied down with packthread”

As mentioned earlier with the invention of the cork screw, modified from a gun worm used to remove bullets and wadding from gun barrels; this and its resultant ability to fully insert the cork plus the evolving cylindrical shape of the bottle allowed bottles to be binned on their sides. This simple change resulting in the cork remaining moist extended its ability to keep the wine healthy and maturing. 

Returning to cider Worlidge first recommends glass stoppers first each ground to a perfect fit with paste of emory powder and oil, (this technology is still used in decanters), as early corks were of variable quality. J Worlidge in Vinetum Britannicum   ” much liquor  being absolutely spoiled by defects in the cork”  However the resultant tight fit of a glass stopper could result in exploding bottles if the cider had not finished fermenting. Each cork manually cut as early hand blown glass bottles had variable sized necks.  It was not until 1740 that moulds were used to create standard neck and capacities.

Robert Hooke another early member of the Royal Society was the first to begin the understanding of why corks were so good. Compressible, elastic and a barrier to water, mould and oxygen. The air cells responsible were visible with the microscopes he invented from glass used to make lens. 

Cork stoppers were recognised to improve the cider with age  Worlidge and Beale recommended cork stoppers and lying the bottles in cool cellars Worlidge suggesting that vaults were made at the bottom of wells. It is known that Lord Scudamore constructed a cellar in his estate with spring water diverted to it to cool his bottles. 

Shakespeare noted the use of corks in bottles  in”  As you like it”  saying

         I prithee take the cork out of thy mouth, that I may drink thy tidings”

Over time  as bottles became more available in the landed Gentry’s houses post 1660 barrels were decanted into bottles and corked to age the wine or cider by the top servant to age it and his name changed with his role from bottler to butler.

There is a delightful story of how Dom Perignon rediscovered the use of the cork. This was when he saw the water bottles of two monks who stayed at his Abbey in Hautvilliers en route from their Monastery in Catalonia ( where it is said the best terroir for growing the best cork is to be found). Prior to that the French used wooden pegs covered with hemp soaked in olive oil. However the French use of cork and Verre Anglais the strong English glass was relatively late and the Duke of Bedford’s household accounts of 25th March 1665 notes  ” Champaign wine 2 dozen glass bottles and corks” three years before Dom Perignon even entered the Abbey! It is more likely he knew of this bottling of champagne from the English who had earlier used cork to stop beer and cider bottles.

Cork is the bark of the Cork Oak tree, Quercus Suber. It grows all over the Mediterranean  but especially well in the Iberian Peninsula. Its use as bottle stoppers as invented by Romans died out as tanners increasingly used it  and resulted in forest depletion in Italy. 

                                  Cork tree stripped of cork from the trunk

Harvesting cork is is a long term industry. Cork cannot be harvested from the tree until it reaches a certain girth. This is about 50 years of age and then harvesting in once every 10 years until the tree finishes its useful life at age about 150 to 200 years.  The harvesting is a skilled occupation. 2 men work in a team and suing axes cut the bark from the ground up to a certain height (which might include some of the lower limbs) in one piece. 

These are then stacked in the forest to weather for several months before being boiled to remove tannins and soften the bark  into flat sheets. These are then dried until the moisture content is right for cutting the cork plugs. Originally this was by hand.

For the cork to be used for corks it must be 2 inches thick and the corks are cut across the grain  so fissures in the cork do mot affect its ability to act as an airtight barrier. The cork oak is the only tree that survives having its bark stripped with a new cambium layer quickly reforming. The other unique feature is a compound  initially called suber. This is in fact a complex of organic chemicals that span across the cell membrane. On the outer side the phenolic domain of hydroxycinnamic acid linked to the aliphatic glyerol domain on the inner surface,  making the cell water and airtight. The cell becoming filled with air as the bark grows on the tree.  The air in the cells makes the cork compressible. This curious quality of cork presumably ecologically gave it an increased ability to resist fire common in its habitat, rather than as a gift for humanity!

The use of corks in England increased significantly after the Treaty of Methuen of 1703  which encouraged trade between England and Portugal where cork growing is centred. Trade was also in corked bottles of Port which improved with ageing  for years. To help perfect the seal the cork and neck were then dipped in wax. 

The use of cork for bottle stopping has now declined with the screw cap and sparkling drink closures such as Zork. This in turn has lead to some cork forests being left untended and the savanna undergrowth rebounding ( it is cut out to allow the cork harvest on its 10 year cycle). The adverse effects of this is the decline in numbers of the Iberian Lynx as hunting becomes more difficult in the undergrowth.