With Cabernet Franc, famous as a blending partner for Cabernet Sauvignon, but much more widely planted in Bordeaux than either. Merlot conventionally makes lush, plummy, velvety wine that can soften Cabernet's more austere frame and, usefully, matures much faster. Very much a wine of the times, it enjoyed enormous popularity in the United States in the 1990s and early 2000s – until usurped by Pinot Noir.

Merlot's homeland is Bordeaux where it is the most important ingredient in most wines qualifying for the basic Bordeaux appellation. But you have to go right up the quality scale here to see Merlot in all its French glory. It may be a luscious, mouth-filling, velvety, plummy, intense Pomerol that can often be positively meaty, almost bloody. Or, typically blended with a bit of Cabernet Franc, it may make up the lion's share of a St-Émilion which is similar but is a little leaner and has more of the rich fruit cake, mineral and torrefaction about it. Merlot tends to be noticeably lower in tannins and acidity than Cabernet, which makes it much more voluptuous to taste and, on the palate, provides lots of fruity impact in the middle to fill in the hole left by the tough, tannic framework of young Cabernet Sauvignon. Despite Merlot's reputation as the user-friendly, early maturing wine, the best of these wines can continue to develop in bottle for decades, and I have been lucky enough to taste a mid 19th century Ch Ausone at the chateau that was as lively as the then chatelaine herself.

Merlot, like the Cabernets, is widely grown throughout south-west France, notably in Bergerac and in Cahors where it is the common blending partner of Malbec. It is also very widely planted in the Languedoc where it can make juicy, plump IGP wines (generally more successful than Cabernet Sauvignon). Just like Merlot the wine, Merlot the vine ripens earlier than Cabernet Sauvignon, but it is less resistant to rot and, if the weather is poor during flowering, can easily suffer from uneven fruit set. It is conventionally but by no means exclusively associated with damp, clay soils.

Much of the world's Merlot is grown in France, but it is also widely grown in north-east Italy, particularly in Friuli where it can make plumper wines than the prevailing Cabernet. Quality varies from basic light red varietals to rich, dense barrique-aged wines, often blended with Cabernet and/or Sangiovese. (This observation is also true of the Merlots produced in Switzerland's Italian Ticino.) Romania, Bulgaria and Moldova also grown significant quantities of Merlot, which can be difficult to distinguish in terms of wine quality, from their Cabernet.

Merlot has been planted at a lick in both North and South America. It has a proven track record in Washington state where its charms are attractively balanced by crisp acidity and good colour. Andrew Will is the most impressive producer here to date.

In California, its fruity charms have been extremely popular when served up as a varietal wine and it is also a popular ingredient in Meritage blends. Its reputation suffered, however, from the very ordinary quality and excessive sweetness of California Merlot at its most basic, as a sort of red Chardonnay. The proposition when California Merlot hit the American market in the early 1990s was basically that this was Cabernet without the pain, a red wine offering the classic nobility of a Bordeaux grape but without the austere tannins. American Merlot's crucial characteristic is not its flavour but its texture which can be, and frequently is, described in one word – smooth. This is a wine to caress the palate, a wine that inspired that great new word in American wine jargon, 'mouthfeel'.

What enabled this of course was the Californian climate. There was no argument, as in Bordeaux, about whether Merlot grapes would ripen fully. The grapes would, in the best examples, be picked as late as possible to achieve full, 'physiological' ripeness, picked not according analyses of their sugar and acid content but by whether the grapes had started to shrivel and their stalks to turn brown and woody. Some of California's finest Merlot producers are Duckhorn, Harrison, Havens, Matanzas Creek, St Francis and Silverado Vineyard, but their wines are in a different stratosphere from the average example which is simply red and sweetish. Merlot has been an undoubted hit with the American public (as witness its phenomenal recent expansion in California's vineyards), even if Californian producers find it so much harder to understand than their beloved Cabernet Sauvignon. Chile has already found its own perfect spot for Merlot, Apalta in Colchagua, and the best-made examples combine California gloss with even more obvious fruit. Chilean Merlot is rarely as alcoholic and 'thick' as the California prototype, but it often has the appetising aroma of a red bordeaux without being quite as weedy/slight/puny. The most inspiring Merlot producer I have come across in Chile is French-owned Casa Lapostolle, whose Cuvée Alexandre and luxury-priced Clos Apalta bring a Pomerol-like opulence to the precociousness of Chilean Merlot.

Argentina's Merlot has a less distinct identity – indeed almost all Argentine red already has inbuilt ripeness thanks to the climate, and so there is little need to augment this with a particularly ripe-tasting variety.

Although Merlot is grown as a blending partner for Cabernet in Australia and New Zealand, few varietal wines of real distinction have emerged, although surely they will. South Africa has already shown just how gorgeous an oak-aged Merlot ripened in a relatively warm climate can be. Merlot is now widely planted in China too.