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Bordeaux 2017 weather re-cap: Advantage Cabernet?

Now that it's time for another Bordeaux en primeur week, we summarise a new report from the oenology unit at Bordeaux University, the ISVV, on weather conditions in the Bordeaux 2017 growing season.

‘This year will long be remembered because of the frost in late April  that devastated nearly half of the potential crop,’ according to the Institute of Vine and Wine Sciences of Bordeaux University (ISVV) 2017 vintage report.

But, as previously reported by Decanter’s Jane Anson, frost damage was patchy – even in the worst-hit areas of the Right Bank and Graves, which sustained more damage overall than Médoc.

While barrel samples are still being tasted, and the skill and resources of winemakers and vineyard managers must be taken into account, the ISVV said that weather conditions set up 2017 as ‘a challenging vintage with great variation’ and ‘undoubtedly more heterogeneous than 2015, and much more so than 2016’.

For the reds, Cabernet was expected to have an edge on Merlot in general in the vineyard, because its later ripening qualities enabled it to get past rain in early September. It was the sunniest October in Bordeaux since 1974.  

For dry whites in Graves, technical data showed that ‘the balance found in the grapes was worthy of the greatest vintages, with perfectly satisfactory sugar levels, high acidity, and a very promising aromatic potential’, the ISVV said.

What makes a good vintage?

There are five conditions that make a great vintage, said the late Denis Debordieu, who was instrumental in the creation of ISVV.

1. An early and rapid flowering and a good fecundation assuring a sufficient yield and the hope of a homogenous ripening.

2. Sufficient hydric stress at fruit-set to limit the growth of the young berries and determine their future tannic content.

3. Cessation of vegetative growth of the vine before colour change, imposed by limited hydric stress and therefore allowing all the goodness from the root to flow into the grapes and not unproductive growth.

4. Complete maturity of the grapes (sugar content among other factors) assured by the optimum functioning of the canopy (leaves) up to harvest time without further vegetative growth (point 3).

5. Good weather during vintage without dilution or rot, allowing full maturity of all grapes including late ripening varieties.

Did 2017 have these conditions in Bordeaux?

Vineyards not hit by the frost had maintained the first two conditions, with quick and even flowering and fruit set, said the ISVV.

Not so many vineyards had the third condition – only those on well drained soils; the summer was dry, but not sufficient for early water stress.

For Merlot, the fourth and fifth conditions were not fully met; the rain in September prevented ideal final ripening in several areas, although vineyards on clay-limestone, with slightly later ripening characteristics, fared better.

For Cabernet Sauvignon, the heat in late September and through October provided good ripening; the fourth and fifth conditions were completed for these wines in many cases, said ISVV.

Bordeaux 2016 weather report

Bordeaux 2015 weather report

2017 in summary by month

January – Cold and dry. Much less rain than usual, and much colder.

February and March – Mild and wet, which lead to early vegetative growth.

April – Started with sunshine but then temperatures dropped significantly, leading to the frost towards the end of the month. This caused a 40% drop in the wine harvest, and some estates are not releasing wines.

May – The return of spring weather and warmer temperatures, which helped flowering. This is where the differences between those hit by frost, and those not, appear.

June – Summer-like, with sunshine and warm temperatures.

July and August – Cooler, autumnal weather. Water stress was delayed, which was favourable to wines hit by frost and gave survivors a chance to catch up. Water stress then came in August.

September – Cool temperatures and more cloud cover than normal with some rain early in the month, which led to concern about rot in Merlot vines.

October – Summer-like weather and the sunniest in Bordeaux since 1974.

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