Cork, agglomerate
A technical cork made up of the remnants from the production of natural corks which are ground down into particles and cleaned and then combined using a food-grade polyurethane glue. A cheaper closure which The Society's buyers discourage suppliers from using.
Cork, colmate
A technical cork made from cheaper-grade natural cork where the naturally occurring pores are filled with ground down cork particles and then the whole is sealed with a food-grade wax coating. Generally only used for wines with a short shelf-life.
Cork, Diam
Diam corks look like agglomerate corks but are far superior and are designed to put an end to cork taint and random oxidation. The production process chops cork into pieces and sorts the superior, highly elastic, suberin component from the less elastic lignin, which is discarded. It mixes the suberin with microscopic spheres of the same substance used for contact lenses, which fills the voids between the cork particles reducing porosity to air and increasing elasticity without introducing humidity. Finally the pieces are mixed with a glue and moulded under pressure. The mechanical properties of the cork are guaranteed for a certain minimum number of years depending on the grade of cork - for example Diam 2 is guaranteed for two years; Diam 3, 5 and 10 are also available.
Champagne cork
The Champagne cork is 90% agglomerate made from cork off-cuts which are ground down, cleaned, compressed and then glued together with two disks of good quality natural cork glued onto the end which protrudes into the bottle.
Natural cork
Natural corks harvested from the cork oak (Quercus suber) forests in Spain and Portugal have been the closure of choice for wine for the 300 years. The bark of the cork oak is stripped from mature trees every nine years. The planks are stored and then cleaned and graded before the corks are punched out of the wood. For wines destined for long-ageing, high-grade natural corks are still the closure of choice.
Cork, plastic
Cost-effective synthetic 'corks' made from food-grade plastic with a silicone coating (similar to that used on natural corks). Generally used for wines for short-term cellaring.
Glass stopper
A glass stopper with a plastic 'O' ring which acts as an interface between the top of the bottle and the stopper, held in place by a metal, tamper-proof seal. Relatively expensive as a closure and not widely used. Can be removed by hand.
Stopper cork (ie sherry)
A short natural or agglomerate cork with a plastic or wooden top to enable the stopper to be removed by hand. Traditionally used for whiskies, sherries, Madeira etc.
Screwcap
Aluminium alloy screwcaps made with an expanded polyethylene wadding for the lining. Screwcaps are also known as ROTEs (roll-on tamper evident) or by the brand name (Stelvin is a popular brand). Widely used in Australia and New Zealand and for wines for short-term cellaring. Becoming increasingly sophisticated in terms of allowing differing levels of permeability so mimicking the properties of natural cork offering winemakers more choice depending of the style of wine being made. There is still a lack of sound data regarding the performance of screwcaps for longer-term cellaring.
Twin top
This is an agglomerate cork with a disk of good-quality natural cork adhered to both ends. A reasonably priced, reliable alternative to natural cork.
Crown cap
This is the metal pilfer-proof cap usually used to seal beer bottles but also used in the production of Champagne and sparkling wine when wines are stored under crown cap before the dosage is added. A few producers use crown caps to seal wine bottles. Open with a standard bottle opener.
