That the wine trade has seemingly been predicting Sauvignon Blanc’s fall from fashion as long as they have Riesling’s renaissance provides a sense of the varieties inexorable rise. Sauvignon – for one – travels well and has adapted to many viticultural regions world over and its popularity keeps growing. Much of its popularity rises from its unique aromatic complexity.
SBIG (Sauvignon Blanc Interest Group), sponsored by First National Bank, recently held a technical workshop with guest speakers Dr Carien Coetzee from Stellenbosch University and Dr Jens Jäger, a former academic and scientist now employed by German closure company Ohlinger, in a R&D and quality assurance role.
Carien presented a review of recent research into Sauvignon and – with screw caps the choice for many producers – Jens on the state of play in the closure business. Since the advent of reductive winemaking, winemakers have gone to great lengths – including the use of costly inert gases – to protect Sauvignon from oxygen at all stages of production. Recent research has revealed the potential folly of such practice.
Carien revealed that oxygen – in the presence of moderate amounts of sulphur dioxide (SO2) however – was conducive to the formation of volatile thiol precursors – thiols are one of the few major compounds responsible for the varieties intense aromatics. This chimes with New Zealand finding higher concentrations of thiols in machine harvested fruit. It suggests winemakers should eschew overly reductive winemaking at the free-run juice stage, while reverting to excluding oxygen during the pressing phase as phenols, for example, increased.
While South Africa was on a par with other countries in the concentration of major thiols, the Cape fell short in one in particular (3MH) which is responsible, among others, for passion fruit aromas, while New Zealand has the highest. Pyrazine concentration – responsible for the greener spectrum like cut grass and green peppers – is similar to other countries.
Oxygen, again within a certain range (7 mg/L), was also found to enhance fresh and fruity aromas in wine until the more widely known loss of these aromas at higher oxidation levels (30 mg/L). However (aromatic) volatile thiols remain present above their perception threshold but are apparently masked by other compounds. The relative concentration of SO2 increases the concentrations of certain compounds.
Carien’s own research also revealed the complex interplay between aromatic compounds where compounds could mutually suppress each other while the varying concentration of one or some could amplify the aromatics of one or others including ‘cooked green’ flavours reminiscent of tinned peas, often used as a descriptor for Sauvignon. She found low concentrations of aldehydes (associated with oxidation) could contribute to the fruity flavour of the wine where there was sufficient concentration of the thiol 3MH. Her doctoral thesis explored how oxidation treatments affected Sauvignon Blanc’s sensory and chemical composition.
Meanwhile research by colleague Elizma van Wyngaard reveals mutual suppressive trends between the volatile thiols and pyrazines which could interest winemakers trying – in attempts to build complexity – to capture both tropical and greener flavours.
Carien’s presentation also revealed that striking a balance in the vineyard also holds its challenges. Typically heat and light are the enemies to many of Sauvignon’s more volatile aromas. Leaf removal around the bunches resulted in wines with more fruity style wines while the shaded bunches delivered wines higher in pyrazines (greener spectrum).
Carien also spoke of Engela Kritzinger’s work and the importance of the tripeptide Glutathione (GSH) in Sauvignon Blanc for its protective effects. GSH limits browning in must, impedes the decrease in important aroma compounds in wine and prevents atypical, ageing off-flavours, suggesting it is very valuable to wine quality. Glutathione is already permitted as part of yeast nutrients while it is expected that pure glutathione additions will be permitted within the next two years.
Engela’s paper also revealed the importance of balance as reductive handling increased glutathione levels in juice (compared with potential loss of thiols). The presentations served to illustrate that the aroma and flavour profile of Sauvignon Blanc wine is the result of an almost infinite number of variations in production, whether in the vineyard or the winery and the tightrope winemakers must walk to make a good Sauvignon Blanc.
Jens focussed on the major factors influencing oxygen permeation of screw caps, starting with a list of factors including the type of liner, texture of the sealing surface of the bottle, shape and geometry of the neck, quality of the capping process, storage and transport conditions.
Winemakers were given a glimpse into the challenges of glass manufacturing learning for example that graphite build up in the mould toward the end of a manufacturing run could cause a rough finish on the sealing surface of the bottle, potentially compromising the seal.
Jens stressed the importance of the capping set up as the margin between a good or poor seal is 1mm. The ideally compression (50%) of the liner leaves 1mm of the liner compressed and 1mm to act as a buffer which could be compromised by excessive stacking of bottles in storage or transport. Excessive temperature fluctuations could also compromise the seal.
Of all the available liners, producers have the luxury of choosing a liner with known oxygen transmission rates (OTR) ranging from tin or Saran-Tin, (very low OTR) to polyvinylidene (PVDC) or Saranex , which allow greater levels of oxygen transmission rates than EVOH, (ethylene vinyl alcohol) to suit the wine’s chemistry and market distribution channel for example. PVDC offers the nominal gas exchange – greater than EVOH – that cork offers without the risk of cork taint where winemakers sought the extra development offered by such gas exchange.
The improved technology of closures, including known performance and risk factors, has brought wine chemistry at bottling to the forefront of winemaking. Winemakers need to consider redox potential for example, including parameters like dissolved oxygen and free or molecular SO2 levels in attempts to better control post-bottling wine chemistry.
Other than for example oxygen, the presentations crossed paths at thiols where both highlighted the need for ongoing research in order to capture and preserve aromatic thiols during fermentation and post-bottling for this a potential game changer for Cape Sauvignon Blanc.
Hanno van Schalkwyk of Vinpro presented on the 2015 vintage. Quality was boosted by very little rot and a cool February. Smaller canopies offered better light penetration and better fruit. Although yield was down smaller berries offered greater concentration of flavours. Producers are excited about the quality of the vintage.
News and information
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Issued by Marlene Truter Communications
Contact: Marlene Truter
tel 083 294 6060