🍷 Screw cap

A screw cap is a closure for wine bottles with an aluminium casing that fits over the outside of the bottle neck. The seal is a liner disc compressed against the bottle rim; the casing holds the liner in place and gives a tamper-evident seal and corrosion resistance. In Australia it is known by the trade name Stelvin: the original French closure was called Stelcap-vin (1959), and the name was shortened to Stelvin in 1978 after the Australian manufacturing licence was obtained in 1970.

The liner decides how much oxygen gets in. It was originally made of PVDC (Saran). The two main liners are Saran Tin, with a fine tin layer, and Saranex. Saran Tin has an oxygen transmission rate of 0.00005–0.0005 cc O2 per day, and Saranex is about an order of magnitude higher, 0.0001–0.001 cc O2 per day. Saran Tin is widely used in Australia and New Zealand, while European producers tend to prefer Saranex because of a perception that Saran Tin can cause reductive characters.

According to the AWRI, screw caps give a consistent, near anoxic oxygen transfer barrier, and wines sealed this way vary less from bottle to bottle than wines sealed with cylindrical closures such as corks. They are much less likely to be affected by haloanisole taint, the class of compounds behind cork taint. Among 2016 International Wine Challenge entries, 89.3 % of Australian wines (n=1,322) were sealed with screw caps, compared with 26.3 % of wines from all countries.