Thiols and beyond: the science of
Sauvignon blanc
Dr Jamie Goode
wineanorak.com
@jamiegoode
@drjamiegoode
The simple story: what makes
Marlborough Sauvignon so distinctive?
•
•
•
Methoxypyazines elevated – greenness
Thiols elevated – passionfruit, grapefruit, tropical aromatics
Good Marlborough Sauvignon is about greenness allied to thiol
aromatic interest
What is a thiol?
•
•
•
•
Sulfur-containing compounds, AKA mercaptans
Organic compounds with a sulfur atom bound to a hydrogen
atom—the SH group (the 'sulfhydryl' or 'thiol' group)
Organic sulfur compounds are smelly, and contribute to fruit
aromas, e.g. blackcurrants, grapefruit, passionfruit and guava
Also play role in roasted coffee, popcorn, grilled meat and beer
Thiols in Sauvignon Blanc
Thiol (and sensory
characteristic)
Perception
threshold in wine
(ng/litre)
Range found in NZ
Sauvignon (ng/litre)
3MH (grapefruit,
passionfruit skin/stalk)
60
100-20 000
3MHA (sweet-sweaty
passionfruit)
4 (below 100,
5-2500
doesn't dominate
– above 100,
impact compound)
4MMP (broom, cat's pee)
0.8
2-50
Factors affecting thiol levels
•
•
•
Formed from precursors present in must by the
action of yeasts
BUT the yeast strain only has a limited effect on
levels
Only a small proportion of precursors are
converted
Factors affecting thiol levels (2)
•
•
•
•
Many factors involved, such as influence of high
UV environment, specific sites, specific vintages
Also machine-picked fruit has x 10 levels of handpicked
Something about machine harvesting increasing
thiol precursors?
Semiochemical effect?
Producing a high thiol Sauvignon
•
•
Protect the C6 green leaf volatiles – precursors of
thiols – by getting SO2 in early
Elevated H2S (hydrogen sulfide) levels early in
ferments (e.g. create a stinky ferment and pipe
that into the fermenter at an early stage)
Preserving thiols
•
•
•
•
•
3-MHA transformed to 3-MH by acid hydrolysis
Temperature of storage a big issue
At 10 C in two years you lose half
At 18-28 C, every two months you lose half
Store wine prior to bottling at 10-12 C?
The complex story
•
•
•
Thiols may not be as important as we thought
Green is more than just methoxypyrazines
Humans are not measuring devices
Wine flavour chemistry
•
•
•
Global wine aroma
Contributory compounds
Impact compounds
Global wine aroma
•20 aromatic chemicals in all wines make global wine odour
•One present in grapes (β-damascenone); rest produced by metabolism of
yeasts
•Higher alcohols (e.g. butyric, isoamylic, hexylic, phenylethylic)
•Acids (acetic, butyric, hexanoic, octanoic, isovaerianic)
•Ethyl esters from fatty acids
•Acetates
•Ethanol (don’t underestimate this one!)
Contributory compounds
•16 compounds present in most wines, but at low
levels
•odour activity value usually below 1 (below detection
threshold), but they have an effect that is synergistic
Impact compounds
•Methoxypyrazines: 2-methoxy-3-isobutylpyrazine (MIBP)
•Monoterpenes, such as linalool, floral, citric aromas
•Rose-cis oxide: characteristic of Gewürztraminer
•Rotundone: gives pepperiness to Syrah, at incredibly tiny
concentrations
•Polyfunctional thiols (mercaptans) - 4MMP, which has a box tree
aroma (4.2 ng/litre detection threshold), 3MHA, which has a
tropical fruit scent (60 ng/litre) and 3MH
The non-volatile wine matrix
Wine constituents that don’t have any aromatic
characteristic of their own influence strongly the way
that the various aromatic molecules present in wine
are perceived
Reconstitution experiments
Work by Frank
Benkwitz, Laura
Nicolau and
colleagues
•Deodorize Sauvignon blanc, then put back compounds
•Omit them in different combinations, e.g. take out all the esters, or
all the thiols, or taking one ester or thiol at a time
•Surprise results: terpenes - make a huge difference to the overall
perception
•Terpenes linalool and α-terpineol had a huge impact when omitted
•They interact synergistically, but individually they are usually below
threshold level in Sauvignon Blanc
Removing esters
Small drop in intensity for most of the descriptors
large decrease in ‘passion fruit skin stalk’ and ‘sweet
sweaty passion fruit’, both of which were previously thought
to be associated with thiols
Green is more than just
methoxypyrazine
• Capiscum (green pepper) – MIBP and C6
alcohols (grassy) and 3MH
• Mixed influence of thiols and other compounds
giving grassy aromas
• Asparagus has an influence from dimethyl
sulfide
Conclusions: Main compounds
in Sauvignon aroma
•
•
•
•
•
•
Polyfunctional thiols
Esters
C6 compounds (hexanols and hexenols)
Methoxypyrazine
Higher alcohols
Terpenes
Thank you for listening
Dr Jamie Goode
wineanorak.com
@jamiegoode
@drjamiegoode