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Beneficial warning ?
In around twenty thousand years, the banks of Lake Geneva have become home to villas and plantings of Chasselas, replacing a sea of ice that was 1000 metres thick. There can be no doubt that Switzerland is currently in a phase of warming. It will last until the next glaciation, in which this beautiful country may well go back to being a mass of uninhabitable, sterile ice. In the meantime, the current warming is fairly good news for winemakers in northern regions like Switzerland. It should be remembered that here, like in many other great winemaking regions (Bordeaux, Champagne, etc..) chaptalisation, the process of adding sugar to the grape juice, was long an authorised, even practically systematic practice. Few people dare to go as far as considering that a little more sun on the vines, as in the sunny vintages of 2015 and 2018, and a little less sugar in the musts, is a good thing, even though the sugar level at harvest is only one of the factors to be taken into account in producing high-quality wines.
A century of data
There are marked differences between global warming and the regional situation. Swiss winemaking regions are fortunate to have reliable statistics dating back almost a century. Since 1925, scientists at Agroscope have been observing and recording the various growth stages (budbreak, the onset and end of flowering, veraison, sugar content at 20 September and at the end of harvest) of Chasselas vines at the Pully research centre. This unrivalled corpus was compiled by Jean-Laurent Spring, and has shown that in 100 years, very early seasons and late seasons have often come one after another. The average budbreak date (development of the bud which marks the end of the vine’s dormant period) for Chasselas and Pully is 13 April, but the extremes range between 19 March (1990) and 5 May (1956, the year of the great frost). Veraison (the moment when the grape changes colour), happens on average on 13 August. Researchers recorded two very late years, 1926 and 1939 (respectively 14 and 20 September) and four very early vintages where the grapes changed colour between 22 and 26 July: 1945, 1952, 2003 and 2011. There is also a broad range in the figures for the sugar content in the grape must. On 20 September, the average for 88 years is 68.8 °Oechsle. And yet, in 1939, the figure was only 43 degrees. On the contrary, 2003 was over 80 degrees on 8 September and was already in the tanks on 20 September. 2018 beat all records, with Chasselas reaching over 87 degrees.
Alternating hot and cold periods
Studies have identified four distinct periods. From 1925 to 1939, late seasons were common: Chasselas began to flower on 22 June on average, and ripening began on 28 August. From 1940 to 1953, the situation changed. Flowering (5 June) and ripening (6 August) began very early, gaining nearly three weeks on the average dates of the previous period. After 1954, the tables turned again, in what was to be three decades of cooler years. From 1954 to 1984, flowering began on average on 18 June and ripening on 16 August. From 1985 to 2012, the dates were closer to the warmer period of 1940 to 1953. The average date for flowering became 13 June, and for ripening 7 August. While the current flowering dates are not as early as in the middle of the last century, the ripening dates are almost identical, which demonstrates a particularly strong warming in summer.
Vin des glaciers
No-one knows why this oxidative white wine from Val d’Anniviers, in the heart of Valais, is called Vin des Glaciers. There is one winemaking technique that has no equivalent in the rest of Switzerland, Spanish solera. This wine was made from Rèze, a traditional Valais variety, up to the 20th century, then from blends of this variety with Ermitage, also known as Marsanne Blanche, Malvoisie, the local name for Pinot Gris, or sometimes Païen, also called Heida or Savagnin Blanc. It is kept for many years in larch barrels. The wine that naturally evaporates from the container or is drunk, is replaced by younger wine.
Swiss Wine Promotion