Viticulture
Merlot grapes are identified by their loose bunches of large berries. The color has less of a blue/black hue than Cabernet Sauvignon grapes and with a thinner skin and fewer tannins per unit volume. Also compared to Cabernet, Merlot grapes tend to have a higher sugar content and lower malic acid. Merlot thrives in cold soil, particularly ferrous clay. The vine tends to bud early which gives it some risk to cold frost and its thinner skin increases its susceptibility to Botrytis bunch rot. If bad weather occurs during flowering, the Merlot vine is prone to develop coulure. It normally ripens up to two weeks earlier than Cabernet Sauvignon. Water stress is important to the vine with it thriving in well drained soil more so than at base of a slope. Pruning is a major component to the quality of the wine that is produced. Wine consultant Michel Rolland is a major proponent of reducing the yields of Merlot grapes to improve quality. The age of the vine is also important, with older vines contributing character to the resulting wine.
A characteristic of the Merlot grape is the propensity to quickly overripen once it hits its initial ripeness level, sometimes in a matter of a few days. There are two schools of thought on the right time to harvest Merlot. The wine makers of Château Pétrus favor early picking to best maintain the wine's acidity and finesse as well as its potential for aging. Others, such as Rolland, favor late picking and the added fruit body that comes with a little bit of over-ripeness.
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