Potential alcohol levels are already highish for Merlot (around 12.5°) but malic acid is still high but slowly reducing. Producers are holding off to harvest next week after the two days of rain forecast this week. The rate of ripening has slowed down and any increase in sugar levels is due to concentration. The levels of colour pigments in the skins and more importantly their extractibility is low but is not improving. The skins are becoming less resistant to any potential Botrytis so for the Merlot there is not much point in waiting too long.
Sugars are increasing for the Cabernet Franc slightly. The skins are stronger for the Cabernets so can be left longer on the vines. Cabernet Sauvignon is so far not ripe with astringent skins and herbaceous notes in the pulp.
Heavy rain (15mm) and strong winds during the night of Sunday to Monday 24 September caused some worry for wine producers in Bordeaux. Today has been largely dry with strong warm winds so the grapes which are in a healthy state so far, have not suffered. Producer’s concerns include bursting of the grapes with the take-on of water (the ground is so dry the soil just seems to be soaking it up like a dry sponge) and the onset of botrytis on the wet grapes. The winds are helping with this and so far there is hardly any sign of botrytis in these cool conditions (nights are exceptionally cool). Rain is forecast all day Tuesday and Wednesday. So we will wait to see its effect.
It should begin to improve with the sun returning on Thursday. Anticyclonic conditions with the sunshine return this weekend. Some will start harvesting any young Merlot vines on Thursday (due to technical director Christophe Capdeville from Brane Cantenac, Margaux). The big start of the 2012 harvest will be on Monday October 1st (weather conditions allowing of course) in the pieds de côtes of St Emilion for example and gravels of Pomerol.
The oenology laboratoties are busy doing analysis for the wine producers of their different vineyard plots measuring total acidity, pH, sugar levels to define potential alcohol, malic acid and nitrogen levels in the grapes (this is determined by the soil, to see if the yeasts during fermentation will need additional nitrogen in the tanks). Although a representative selection is picked from a plot the marked lack of uniformity in ripening within plots means that results are not that representative. It is best this year to get a feel for ripeness levels in the vineyard plots witha lot of tasting of grapes.