Every four years or so, Penfolds, Australia's foremost premium wine producer, based in the Barossa Valley, flings the cellar door wide open and invites a handful of guests to take a peek at all the wine produced since 1953.
At times gruelling, always fascinating, three and a half days of tasting alongside chief winemakers John Duval and Peter Gago offered a unique chance to chart the development of the famous Penfolds bin numbers over a generation and beyond.
Aptly, the experience is called The Rewards of Patience. It is a common theme of great European wines that patient cellaring brings rich rewards. But given that Australian wine has made its mark for, pardon the expression, drinkability, it's ironic that such an enviable reputation can sometimes obscure just how well Australian wines can age.
You might expect such feats only of the aristocratic Grange and Bin 707. The surprise was to see how gracefully mid-priced wines such as Bin 28 Kalimna Shiraz and Bin 389 Cabernet Shiraz can also evolve.
Across the range, there is a consistency that defines the Penfolds style, whether at the Grange or Koonunga Hill level of quality. The hallmarks are not so much subtlety, but, from the mid-1980s in particular, richness, power and flavour.
Penfolds reds are largely based on the shiraz grape (the syrah, that is, of the northern Rhone) with its black fruit, spice and berry flavours. Barossa Valley shiraz is at the heart, some might say soul, of Grange itself, and St.Henri, Bin 28, Bin 2 and Koonunga Hill. American oak with its special chocolate, vanilla and coffee sweetness, is a core feature of the style too. French oak adds polish to the understated styles of the Magill Estate and the new, yet to be released, Barossa Shiraz.
There are variations on the theme. Bin 128 uses shiraz only from Coonawarra (Australia's most famous wine region), Magill Estate from the original Adelaide vineyard only. Bin 707 is pure cabernet sauvignon and Bin 389 a blend of cabernet sauvignon and shiraz.
The biggest variable from one year to the next is vintage. The differences are not normally as marked as in Europe's classic wine regions, initially at least. Nevertheless, Australia has its great and its mediocre vintages and each year leaves its special imprint on the wines. Halfway through the tasting for instance, both 1982 and 1989 showed a marked love-it-or- leave-it blackcurrant cordial-like character.
At the affordable price level, Bin 2 Shiraz Mataro and Rawson's Retreat are best in the first three years of exuberant primary fruitiness. The mid-priced popular classics such as Bin 28, Bin 128 and Bin 389 reach a peak within three to five years and mature for another five and sometimes longer.
The voluptuous 1996 vintage of the cabernet-based Bin 389 for instance, still needs a year or more, but judging by its evolution between 1983 to 1994, will remain a deliciously drinkable wine for 10 years or more. Even the best older vintages of Koonunga Hill, which is at its best in three to five years, keep going strong.
Grange's alter ego, St Henri Shiraz, is one of the big surprises of the tasting, partly because it's not well known in this country, but also because it's about a third of the price of Grange. Traditional by contrast, largely because it's matured in old oak casks, it's a pure expression of shiraz and excellent in the 1990s.
Bin 707 Cabernet Sauvignon can be as long-lived as Grange in great vintages such as 1964, 1966 and 1976, and, although made from Bordeaux's cabernet sauvignon grape, its sweet American oak flavours allied to an opulent cassis fruit quality differentiates it sharply from claret. From the mid- 1980s, it gets better and better, notably in 1986, 1990, 1991, 1994 and 1996.
Grange itself is a wine of extraordinary staying power. Developed by the late Max Schubert in 1951 from an experimental batch of shiraz grapes and aged in small American oak casks, Grange has become an icon, with prices to match, not least because Schubert continued to defy company orders to cease production. Tough and tannic in its youth, the great vintages of the 1990s (1990, 1991, 1994) are taut and muscular.
It takes Grange a decade to hit its stride, gaining in complexity, flavour and texture in outstanding years such as 1971, 1976, 1978, 1980, 1983, 1986, 1988. Tasting the great old vintages - 1953, 1955, 1963 - is like luxuriating in a comfortable leather sofa. Infinite patience required, but the rewards are worth it.