The story of Zinfandel is like a romantic thriller, a mystery I have been following over the last 30 years and one that was solved only a very few years ago.
By the middle of the 19th century a vine variously called Zinfandel and Zinfandal had established itself in northern California and was prized for its productivity. A visiting French winemaker even pronounced that its wine was "like a good French claret". It thrived in the warm climate, was beloved by the thousands who shipped grapes east from California to make wine at home during Prohibition, and was the most planted dark skinned grape variety of the West Coast until usurped by the more glamorous and, significantly, more obviously French, Cabernet Sauvignon in the second half of the 20th century.
It was the fact that no relationship could be found with any known French variety, and there was therefore no reference to it in France's well-kept and documented vine collections, that kept Zinfandel's origins shrouded in mystery for a century and a half. It was left to historians rather than scientists to try to re-trace the path by which this popular variety made its way to California.
The most dogged of them, Charles L. Sullivan, worked out by poring over old catalogues and nurserymen's records that the vine had been imported to the American east coast in the late 1820s from the Austrian imperial nursery in Vienna. It was then taken to Boston and by the 1830s was quite widely grown under glass as a table grape in New England. It seems as though the variety was included in an early shipment of vine cuttings to the hundreds of prospectors who rushed out to California in search of gold in 1849 and had to turn to farming instead. Sullivan found a connection with a vine known as Black St Peters in New England but couldn't work out how Black St Peters found its way across the Atlantic.
The next significant chapter in the unravelling of the mystery came in the early 1990s when, once DNA profiling had been applied to analysing the genetic relationships between different vine varieties, it was established beyond doubt that Zinfandel was, intriguingly but inexplicably, identical to a then-obscure grape variety called Primitivo grown on the heel of Italy. Theories were advanced for how this could be. Did Italian immigrants in the US ship or take cuttings back from California to Puglia? There followed some years of speculation, which did not stop some Pugliese exporters labelling their Primitivo varietals destined for the US simply "Zinfandel", hoping to cash in on the established market for the California variety there.
The breakthrough came when it was established that Zinfandel/Primitivo had to be a parent of the Croatian variety Plavac Mali. The other parent turned out to be a much more obscure Croatian variety, which led researchers to the conclusion that Zinfandel/Primitivo had to be Croatian in origin too. Eventually, after many a trek through the vineyards of the beautiful Dalmatian coast and its rocky islands, the doppelgänger was found. Croatian viticultural researchers, acting in conjunction with Professor Carole Meredith of Davis, discovered an ancient and almost extinct variety on the island of Kaštela near Split called Crljenak Kaštelanski (literally “red grape of Kaštela”) that did indeed prove to be identical to Zinfandel.
All of this happened in parallel with some extraordinary developments in the commercial history of Zinfandel. Because it had been so common in California, it was not at all revered. In fact beside Cabernet it was regarded as a sort of home-grown weed, good enough for the common man if cheap enough, but incapable, unlike the fashionable and aristocratic Cabernet Sauvignon, of producing fine wine.
The only saving grace for the reputation of "Zin" was in some extraordinary Port-like essences made from some of the oldest vines in the state, made from ancient vineyards left virtually untended during Prohibition in the old mining country of the Sierras east of the Central Valley. Most of these wines were labelled Late Harvest Zinfandel and regarded as freaks in the 1970s because they reached natural alcohol levels in excess of 15% (heaven forfend).
Zinfandel's stock slumped and there seemed nothing useful to be done with the thousands of acres planted except bleed as much lowly, thin red from them and blend them with more prestigious grape varieties, or sell them as cheap Hearty Burgundy and the like.
Then in the 1970s the white wine boom kicked in with a vengeance and someone had the bright idea of bleaching most of the colour of red Zinfandel, or bleeding the juice off the skins as fast as possible, and "White" (actually pale pink) Zinfandel was born. The Trinchero family based their fortune on this one commodity but they were far from the only ones to benefit from this new American craze.
By the end of the 20th century White Zinfandel's fortunes had firmly waned and most Americans now realise that Zinfandel can and should be a red wine. But what sort of wine? Zinfandel has two potential problems viticulturally. Unless it is severely pruned, it tends to yield too many grapes to make concentrated wine – in fact there is a particularly recognisable berry jam flavour in many an inexpensive California red (some of them labelled with the names of other grape varieties) that is a sure sign of the presence of some high-yielding Zinfandel in the blend.
Zinfandel's other problem is uneven ripening, even on the same, tightly packed bunch of thin skinned grapes. The grapes can therefore rot quite easily and when grapes are ripe they can easily start to raisin. So although it commands lower prices, Zinfandel needs more care in the vineyard than Cabernet Sauvignon.
The best California Zinfandel tends to be grown from very carefully tended old vines grown in the Sierras or in Dry Creek Valley although there are pockets of great vines elsewhere. So high is Zinfandel's profile in California that it is planted in many other warmer wine regions in the USA as well as in South America, South Africa and Australia, all of which have a warm enough climate for it to ripen fully.
In Puglia, Primitivo has its supporters but has to compete, or be blended, with Negroamaro. Its homeland there is around Gioia del Colle and is popular as both a DOC and IGT velvety red which has many fans around the world.
By Jancis Robinson