In 1770, during his voyage to New Zealand, Captain James Cook would discover a stretch of land spanning New Zealand’s South Island, to the south of the Marlborough Sounds and north of Clifford Bay. Cook’s discovery coincided with regional flooding, which washed large amounts of sediment into the sea. Noticing the water’s opaque appearance, Cook christened the area Cloudy Bay. Cloudy Bay’s name was later officially altered to Te Koko-o-Kupe / Cloudy Bay, with the Māori name a nod to the early explorer Kupe. 215 years later, seasoned winemaker David Hohnen, convinced of Cloudy Bay’s potential to produce great wine, invested in the best land the region had to offer and established Cloudy Bay Winery. Now under the ownership of LVMH, many consider Cloudy Bay to be amongst the world’s best Sauvignon Blanc, including wine writer, George Taber. Defined in part by mouthfeel, Cloudy Bay Sauvignon Blanc also boasts intense, concentrated fruits, namely grapefruit, passionfruit, and guava. Joining via Zoom, following the recent launch of Cloudy Bay Sauvignon Blanc 2020, winemaker Daniel Sorrell told how chasing one particular thiol, 3MH, has come to help shape these defining characteristics. In this article, I examine thiols in more detail and explore more closely how Cloudy Bay chase 3MH.

Defining wine aroma and Sauvignon Blanc

Tempting though it may be, simplifying wine aroma to single compounds and contributory factors can be somewhat unhelpful, and almost certainly negates the spectacular interplay between the natural world, complex chemistry and the human hand. Jamie Goode helpfully splits wine aroma chemicals into three main groups. These are global wine aroma, contributory compounds and impact compounds. Though all equally important, impact compounds are in a sense particularly interesting. These compounds are prominent varietal indicators, pointing rather reliably toward specific wines. Particular varietal wines are marked by easily-recognisable impact compounds. Riesling by TDN, Syrah by Rotundone, and Marlborough Sauvignon Blanc by thiols.

Thiols, the word a portmanteau of thio and alcohol, are the sulphur-containing (organosulfur compounds) analog of an alcohol. For general purposes, they can be divided into two groups; those with negative smells and those that contribute positively to a wine.  The sulphur-containing compounds that contribute positively to wine are known as volatile thiols.

Unlike most aroma compounds found in wine, volatile thiols are unique in the fact that they exist only in trace amounts in the berries.  Aside from a small amount of 3MH (approximately 100 ng/L) found at harvest, the other compounds are virtually nonexistent in grape juice. This formation throughout fermentation as a yeast byproduct has been the focus of considerable amounts of research. From this, it has been identified that direct precursors become cysteinlated or glutathionylated for each compound during fermentation.  More information about these precursors can be found at UC Davis Waterhouse Lab.

Not all thiols are equal

There are four volatile thiols primarily responsible for Marlborough Sauvignon Blanc’s distinctive aroma profile. Methoxypyrazines are also important in the style of some Marlborough Sauvignon Blanc, these are compounds responsible for Sauvignon Blanc’s sometimes prominent vegetative aroma. With this in mind, certain thiols are more preferential than others, particularly in achieving Cloudy Bay’s intense, fruit-forward, passionfruit style. The most important in achieving this is 3MH, the four in their entirety are as follows:

Thiol	Aroma	Range (ng/L)	Threshold (ng/L)
3-Mercaptohexan-1-ol (3MH)	Grapefruit, passion fruit, gooseberry, guava	26–18,000	0.8
3-mercaptohexylacetate (3MHA)	Passion fruit, grapefruit, boxtree, gooseberry, guava	0–2500	60
4-methyl-4-mercaptopentan-2-one (4MMP)	Boxtree, passion fruit, broom, black current	4-40	4.2
4-mercapto-4-methylpentan-2-ol (4MMPOH)	Boxtree, broom flower; cat pee	0-40	0.8

At Cloudy Bay, not all of these thiols are considered equal in the amount to which they are desired, or in fact, desired at all. More particularly it is 3-Mercaptohexan-1-ol (3MH) that Daniel Sorrell and his team favour. Their work in both the vineyard and the winery can be thought of to some extent as chasing 3MH. It is this 3MH thiol which is an integral component to overall wine style, it also happens to be what I find aromatically compelling.

Chasing 3MH

At Cloudy Bay, vines are usually cropped lower than neighbouring vineyards with lower average yields across the board. Sorrell is keen to make clear that this is neither right nor wrong, it is merely what is required to achieve Cloudy Bay’s more concentrated, intense, 3MH-centric style. This lower cropping means earlier ripening which in challenging vintages such as 2020, where irrigation supplies are limited, places the vines under less hydric stress and means they are often picked post-drought.

Considering these volatile thiols are present in grapes in only trace amounts, it is the formation pathway of their aromatic precursors which guides much of Cloudy Bay’s work in both the vineyard and the winery. These precursors can be manipulated by certain viticultural practices or winemaking decisions. Cloudy Bay’s grapes are machine harvested, this allows them to pick at night when temperatures are cooler and to get grapes to the winery significantly quicker. 3MH and 3MHA in wines made from juice obtained from machine-harvested fruit have been shown to be 80% higher than those hand-harvested. Jamie Goode has also suggested that machine-harvesting could favour thiol precursors based on disruption during picking resulting in enzymatic changes which favour precursors. Or more interestingly, that machine harvesting may trigger the release of semiochemicals which warn vines upstream, resulting in physiological changes and increase in precursors.

A small percentage of the juice at Cloudy Bay is fermented at slightly higher temperatures in oak to which has been shown to help maximise 3MH thiols. Higher fermentation temperatures (irrespective of the yeast strain used) have been shown to result in increased volatile thiol concentration when compared to lower temperatures. The wines are all inoculated with selected yeast strains and harvest dates tend to be earlier, precursor concentrations are shown to peak at a semi-ripe stage prior to grape maturity.

Furthermore, the addition of Sulfur dioxide is considered and employed to stabilise 3MH, bottles are also sealed under Stelvin. The AWRI has studied thiol in more detail and a more detailed analysis of preserving and maximising thiols is available here.

Both 3MH and 3MHA thiols are known to diminish rapidly over just one year in the bottle, after this time less-rapidly diminishing compounds, such as methoxypyrazines where present, can come to dominate wines sensory profile. It has also been suggested, with some supporting evidence, that methoxypyrazines may also stifle 3MH thiols. When asked why customers should be comfortable paying £24 for Cloudy Bay, Sorrell’s answer was multifaceted. He posited that a great deal of effort is taken to maximise and preserve both 3MH and 3MHA thiols, a similar amount of effort is taken in reducing levels of methoxypyrazine. This combination of efforts means that Cloudy Bay’s wines possess impressive ageability. Sorrell, perhaps controversially, went as far as suggesting that their ageing capacity is more superior than that of Sancerre.

Much of the work undertaken to reduce methoxypyrazine levels concomitantly increase precursors to 3MH thiols. Water is tightly regulated at Cloudy Bay, too much water can result in excessive vine growth and subsequently enhanced cluster shading. All of the aforementioned have been associated with high MP levels in studies. In the vineyards, Cloudy Bay place a great deal of emphasis on appropriate canopy management prior to veraison, reducing leafing around the fruit zone to increase ripeness. This has been shown to reduce MP levels at harvest. Maximising fruit-zone exposure also increases 3MH thiol precursor and makes picking early feasible. More information on how viticultural factors affect methoxypyrazines can be found here.

These are technically-superb wines, considered and well-intentioned. From vintage to vintage consistency is a defining factor alongside a concentrated, fruit-forward aromatic profile. Though it may be tempting to overlook Cloudy Bay, given the unhelpful caricature of it as a ‘mainstream’ wine, I would advise those who have strayed to return and revisit. Cloudy Bay 2020, the result of a blend of more than 90 parcels of Marlborough Sauvignon Blanc, 4% of which is fermented in oak, is available now for £24 from Clos19.