I wonder how many of the wine drinkers who lap up Australia's rich, sturdy Shirazes realise that they are made from the very same grape as some of France's finest, and rarest, reds, the twin jewels of the Rhône Valley, Hermitage and Côte Rôtie? The grape is known in the Rhône as Syrah and may well have been grown there since Roman times. It is certainly well-adapted to the steep terraces by the side of the river Rhône around Ampuis for Côte Rôtie and Tain for Hermitage, in each case on vineyards carefully angled to make the most of the available sunshine. For this northern bit of the Rhône can be so much cooler than, for example, Châteauneuf-du-Pape 150 km (93 mi) to the south. Hermitage was such a famously majestic, robust wine in earlier centuries that it was sometimes used to strengthen the feeble ferments of Bordeaux, such wines being described as having been 'hermitagé'. This deep, dense, long-living wine is made exclusively from Syrah and, if labelled J L Chave, Paul Jaboulet Aîné La Chapelle or Chapoutier Le Pavillon, can easily age as long as a good classed growth bordeaux.

The trademark flavour of French Syrah is black pepper. A good Hermitage certainly has this in spades, but can mature into something more redolent of leather and, in very ripe years, spice. Côte Rôtie is different again. Traditionally it was the stereotypical female to Hermitage's very obvious masculinity – indeed a small proportion of heady white Viognier grapes were used to perfume and lighten the blend. Today, you can still find these delicate, very fine reds in Côte Rôtie (try to get your hands on a Gangloff bottle, for example), but the king of the appellation Marcel Guigal has distracted many of us from the original style. He worships oak and mass, so that his world-famous, fabulously-priced, single-vineyard Côte Rôties La Mouline, La Landonne and La Turque can be as intense or even more intense than many a Hermitage.

The best-value French Syrah, by far, is a Crozes-Hermitage, from the outlying vineyards of Hermitage, made by one of the region's many ambitious producers. Graillot is an obvious example, although Pochon and Belle are also reliable. They make ultra-glossy, juicier, earlier-maturing cousins of Hermitage.

Less exciting examples of Syrah from the Rhône Valley and its fringes such as the Ardèche can be pale and thin and the appealing black-pepper scent is often replaced by the much less appealing smell of burning rubber. This may be because the vines are being over-produced or are simply too young.

In the southern Rhône, around Châteauneuf-du-Pape in appellations such as Gigondas and Côtes-du-Rhône-Villages, Syrah plays an important though usually subordinate role, typically adding structure to the dominant Grenache grape and other local specialities such as Mourvèdre – for Syrah grapes are relatively small and high in colour and tannins. There are signs that Syrah is falling out of favour relative to Mourvèdre in Châteauneuf-du-Pape.

But Syrah's role in the vineyards just to the west of here can be glorious. Of all the so-called cépages améliorateurs (improving grape varieties) that have been encouraged in the Languedoc, Syrah has proved most at home. In fact, unlike Cabernet and Merlot for example, it's allowed in to all the fine red appellations – the likes of Costières de Nîmes, Languedoc, Faugères, St-Chinian, Minervois, Corbières and Fitou – and accounts for an ever-increasing proportion of them, replacing tough old Carignan to make reds that are positively voluptuous – and by no means expensive. It seems particularly successful in Costières de Nîmes and in the higher vineyards of Pic St-Loup and La Livinière (these two villages within the Languedoc and Minervois appellations respectively).

Apart from this great swathe of south-eastern France, Syrah's other important dominion is Australia, where it has been known as Shiraz for generations. Visitors from Tain l'Hermitage confirm that the vines are identical to the Syrah of the Rhône, but the wines certainly aren't. If black pepper is the French trademark, dark chocolate is that of Shiraz produced from one or, more often, some of Australia's hotter vineyards. Barossa Valley Shiraz can be positively unctuous – so rich in fact that some producers deliberately add tannin to give the wines backbone. Many of these wines are very obviously inspired by the essence that is Australia's most famous wine, Penfolds Grange, an amazingly concentrated elixir put together from top lots of Shiraz grown in various locations in the state of South Australia. It can last for decades and commands prices easily as high as first growth bordeaux. Henschke is another infallible name for South Australian Shiraz, with their bottling from the antique Hill of Grace vineyard (not a hill at all in fact) rivalling Penfolds Grange in the auction room.

The quality of Barossa Shiraz was responsible for the much-needed re-evaluation of this grape variety in Australia. (As recently as the 1980s it was so common than Australians couldn't believe it was worth half as much as fancy French Cabernet, a much more recent import.) Nowadays Shiraz is recognised as one of Australia's great wine assets, although to be really interesting it needs to come from a site with more character than the irrigated inland regions whose produce is typically labelled 'South Eastern Australia'. McLaren Vale is on a roll with its warm, welcoming-yet-deep-flavoured Shiraz at the moment, and d'Arenberg makes some of the best-value. The cooler vineyards of the state of Victoria such as Mount Langi Ghiran and Craiglee make great wine that has some of the black pepper of good French Syrah with the weight of a South Australian Shiraz. In New South Wales, Shiraz was the red wine grape of the historic Hunter Valley where the wines were so strapping, and often so lacking in focus, that they inspired that memorable tasting term 'sweaty saddle'. There are still bottles hidden in ancient cellars attesting to the staying power of the wines that were then called Hunter 'Hermitage'.

But what's this? Decided changes on the Syrah/Shiraz scene. Wines as good as those described above are, inevitably, inspiring ambitious wine producers around the world. There is feverish activity among California's so-called Rhône Rangers, with some fine Syrahs being produced by the likes of Qupé, Joseph Phelps and Jade Mountain. In South Africa, Syrah has proved extremely adaptable with wines such as Stellenzicht, Simonsig and Saxenburg suggesting that, as in the Languedoc, the variety might well be better suited here than Cabernet Sauvignon. These producers generally label their wines Shiraz but some South African (and Australian) producers of particularly transparent, refreshing examples tend to label them Syrah.

And we can now choose Syrahs from Spain (notably Marqués de Griñón), a raft of examples from Chile (where the variety was pioneered by Errázuriz), central Italy (L'Eremo from Isola e Olena and some other stunning examples), Portugal (Cortes de Cima), Washington state (Red Willow) and Switzerland (Germanier). The most common fault in early vintages of this grape is to let it get overripe, which it can do rapidly, producing rather sickly, flabby wine. But today we can choose from a wide variety of titillating examples from all over the world.