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Thiols hit the high notes

Published:  18 January, 2007

What a difference 2.2g makes. This is the amount of iBMP, a methoxypyrazine, estimated in the 2005 Marlborough Sauvignon Blanc harvest. Giving the green pepper and herbaceous notes that have helped propel the popularity of the region's flagship varietal, iBMP is just one of the elements being scrutinised in New Zealand's Sauvignon Blanc study, the results of which could herald new styles and Super Sauvignons'.

The aim of the six-year multidisciplinary research programme is to improve the consistency and quality of New Zealand Sauvignon. Now in its second year, preliminary findings are being released, many of which were unveiled in New Zealand last month at the International Cool Climate Symposium.

A major focus is to identify and quantify Kiwi Sauvignon's main flavour and aroma compounds - no mean feat considering the low levels at which these potent components are found. Marlborough may have harvested only 2.2g, but early results of the programme's chemical analysis of Sauvignons from New Zealand and beyond, show the native iBMP count to be much higher than those of the other countries in the study.

Topping the test were the Sauvignons of Wairarapa, with Marlborough's close behind. Sauvignons from Hawkes Bay and Australia registered much lower iBMP levels, with those of France, South Africa and the US registering lowest.

Part of Marlborough Sauvignon's success lies with the volatile thiols, such as 3MH, 3MHA and 4MMP, which complement these methoxypyrazine characters. Until the mid-1990s little was known about these thiols, generated from the interaction of precursors in the grape with yeasts during fermentation and responsible for cat's pee and passion fruit notes.

New compounds may still be found, but of the known thiols tested, much higher average levels were found in Marlborough Sauvignons - well above those of Wairarapa and way ahead of Hawkes Bay and the other countries. Cross-referenced with sensory data and the winners of the Air New Zealand Wine Awards, a definite preference for Sauvignons with elevated thiol levels was highlighted. Maybe the two South Africans should have spiked their Sauvignons with thiols instead of methoxypyrazines.

Sensory panels play a key role in the research, providing information on perceived characteristics and consumer preferences within Sauvignon flavours and aromas, which are then correlated with the chemical data. Results from the initial New Zealand-based sensory study rate Marlborough Sauvignons most highly, followed by those of South Africa and, interestingly, Wairarapa's last. Top-ranking wines were those with overt cat's pee and passion fruit thiol notes.

With the recent shift in Marlborough Sauvignon to more tropical styles, it's encouraging to see that this is being referenced back to the consumer, whose tastes (in New Zealand at least) seem to be in accord. Whether this is true across international markets is something that should be uncovered by the study's future investigations.

Panels are also being used to test the parameters of desirable flavours emerging from the programme's concurrent viticultural and winemaking research. Conclusive results from viticultural trials are years off yet, but experiments are underway to gauge the influence of management and site on Sauvignon styles, which could be considerable.

Yeasts and their capacity to convert thiols into volatile compounds is the focus of the study's winemaking research. 'Thiols have much potential for manipulation - only a small fraction of the precursors get converted,' says Professor Richard Gardner, who heads the programme as well as its yeast research.

As well as looking at how efficiently commercial yeasts convert thiols, the research could see the development of new strains with higher conversion capacities. This would enable winemakers to tweak Sauvignon styles towards certain flavour profiles, selecting yeasts to enhance or suppress chosen characters. Enter 'Super Sauvignons' and the rise of new dimensions in the variety's flavour spectrum.

While the terroir at the heart of New Zealand Sauvignon cannot be replicated, data and strains could be used by competitors in less thiol-rich winegrowing regions, a concern I put to Philip Manson, science and innovation manager at New Zealand Winegrowers. But Manson is confident that the country's Sauvignon is enough of a benchmark to withstand the threat of foreign pretenders applying any Kiwi-led advances: 'If you want the original there's only one place to go to. New Zealand.'