It was one of those penny-drop moments.
We were tasting two glasses of pinot noir, blind, and the questions were: is there any difference between them? If so, how are they different?
Glass One was full purple-red in colour and smelled fresh and fruity, delightfully primary, with a bright raspberry aroma that was almost like bubble gum. It was pristinely clean, delicate, light on the palate and charming, but ultimately rather simple.
Glass Two had a darker colour and blacker fruit aromas, more complex and mysterious. Similarly, in the mouth it was fuller-bodied, richer and deeper, with greater textural interest, fleshier and denser, with more tannin. A beautiful wine, too, but much more profound and captivating than Glass One.
Winemaker David Bicknell then announced to the gathering that the only difference between the wines was that Glass One had been fermented with a pure yeast strain and Glass Two had undergone a wild ferment. That means no yeast had been added: the juice had been fermented by whatever yeast strains happened to be in the air at the time.
''Both wines were picked from the same Upper Yarra Valley vineyard on the same day, and everything in the winemaking was the same except the yeast,'' announced Bicknell, who is the winemaker at Oakridge. The class was asked to try to pick the wild ferment and say which wine they preferred. The great majority nominated the correct glass, and liked it more. There was nothing wrong with Glass One: it was simply that Glass Two was better - every way you looked at it.
The ''class'' was a wild-yeast workshop at the recent Australian Wine Industry Technical Conference in Sydney. The ''students'' consisted mainly of experienced winemakers. No average class.
It was the first time I'd experienced such a stark demonstration of the effects of wild ferments - which some people call natural ferments (although all fermentations and all yeasts are surely natural). Some prefer to call ''wild'' yeasts ambient or indigenous yeasts. There are arguments over the naming.
Suffice it to say that the environment, especially the air, contains hundreds of thousands of strains of yeast, most of which occur naturally. The species present depend on what flowers, fruits, trees and grasses are in that locality. Recent New Zealand research has shown that yeasts are territorial, and the species present vary according to the place. Hence, some argue, yeasts are part of the ''terroir'' of wine, just as soil and local climate are. Theoretically, wines taste different according to their ''terroir'' - and different-ness (or somewhere-ness) is a highly prized thing in top-end wine. Every winemaker wants to prove his or her wine is unique.
Back to the workshop, which was organised by Paul Henschke and Chris Curtin, research microbiologists at the Australian Wine Research Institute. During the workshop we were served 30 wines, some of them purely experimental, others intended to be commercial. Pairs of Hardys' Eileen Hardy chardonnay and Mount Pleasant Hunter chardonnay, all 2013 vintage, one of each ''wild'' and the other seeded with cultured yeast, showed more permutations of character. With Mount Pleasant, the wild wine was cloudy in appearance, and quite stinky, but also showed density of flavour and richness, while the regular wine was good but not as interesting. The winemakers seemed to think the stinky one would clean up after a period of lees-stirring.
Of the Hardys wines, the regular ferment looked bright and clear in the glass, and was pristinely clean, intense and lively, with a spring water-like lightness of texture. The wild ferment was cloudy, smelled of cashews, bread, smoky oak, sulfides and spices, but the real difference was in the mouth. Its texture was far more rich and dense, fleshy and rounded, smooth and harmonious.
Eileen Hardy winemaker Tom Newton said he believed the sulfides were related to the wine's greater textural density. Indeed, all winemakers I've quizzed who practise wild fermentation believe it gives their wines greater length of palate and improved texture as well as extra flavour complexity.
Even riesling responds to this ''rougher than usual handling''. Kerri Thompson's wild-ferment Clare Valley riesling was a graphic illustration. Served beside a conventional Clare riesling, which was a perfectly good wine in its way, her KT Pazza Riesling 2013 was turbid (not clear) and smelled of apple, pear, yeast and a hint of nuttiness from time spent in old barrels. It was a more expressive, more textural and more layered wine than the conventional one. It's on sale soon at $29.
And perhaps the most beautiful, exotic, fascinating wine of the day was Cullen's Kevin John Chardonnay 2011. This was slightly feral and very exciting. It lives dangerously. Biodynamically grown and wild fermented, it's a pioneer and benchmark of the genre. It's so complex it's difficult to describe, although honey and oak and what I call ''balsamic'' (like the smell of balsamic vinegar, without the vinegar or sweetness) aromas are all involved, welded to a razor-sharp, crisply tart, long and linear palate structure.
It's a great wine. But is it great because it was wild fermented? Probably the reason for its greatness is a combination of factors: great vineyard site, mature vines, expert viticulture and winemaking, and wild ferment are some of them.
If all this sounds esoteric and a bit like navel-gazing, winemakers don't believe drinkers need a crash course in microbiology in order to enjoy their wines.
Wild ferments are just one of many things winemakers experiment with in their constant quest to make better and better wine for our delectation.
Where the wild things grow
If wild ferments give so much better results, you might wonder why winemakers ever moved away from them. There are reasons. Pure yeast cultures were developed to make winemaking easier, with more predictable and consistent results. This was and still is the best way to mass-produce large volumes of inexpensive wines. Pure yeast cultures (just one strain of yeast conducts the entire fermentation) provide greater reliability than wild ferments (in which there could be hundreds of strains). Wild ferments can produce strange, even bizarre, aromas and flavours. It seems to make sense, though, that single-yeast ferments produce simpler wines.