When I was researching my post on Australian aged rieslings, Buy Wine Ideas: Australian Aged Reislings: Beautiful Expressions of Terroir 28 July 2011, I came across a very good explanation about the merits of bottling wine under screwcap on the Pewsey Vale website.
James Halliday notes that Pewsey Vale was the first winery to bottle its riesling under Stelvin screwcap in 1977. Unfortunately the screwcap was not well received by the public and the initiative was put on ice for almost 20 years. Now, of course, use of the screwcap in Australia, especially for white wines, is considered best practice!
Below is a description of the benefits of the screwcap with respect to Pewsey Vale The Contours Riesling, one of Australia’s best rieslings, which is only released after five years of bottle age. It is made by Yalumba’s Chief Winemaker, the multi-award winning Louisa Rose. According to Halliday, “Pewsey Vale never lost faith in the technical advantages of the closure. A quick taste (or better, a share of a bottle) of five-to-seven year-old Contours Riesling will tell you why.” (James Halliday, Australian Wine Companion 2011 Edition).
Sealing a bottle under a screw cap removes the variability and taints associated with cork. A screw cap also ensures that the wine in the bottle will age under the best possible conditions. The perfect seal of the screw cap ensures that no air or oxygen can enter the bottle. In these reductive conditions the wine undergoes “pure bottle aging” where the fresh citrus flavours remain, and are overlaid with flavours of toast, lemon grass and eventually some honey and possibly marmalade. Since there is no oxygen getting in to the bottle, there is no oxidising or “drying out” of the wine. This means that the colour, while it will deepen into the gold spectrum, retains its freshness and green hues. The flavours and palate do not “dry out”, but stay fresh with any sweet fruit characters that were initially in the wine remaining. A hint of toast overlies the still intense lime and citrus fruit. Citrus dominant, lime juice and marmalade finishing with a crushed stone minerality. The wine is only just showing the first signs of bottle age after 5 years, indicating that there is still a long future in front of it. Clean and dry with refreshing natural acidity. Pewsey Vale website.