Thiols
Having worked in the wine-industry in Marlborough you’ve probably heard the word ‘thiol’ been talked about by every wine-maker and his dog. But what is a thiol? And why is it so important in making that typical Marlborough Sauvignon blanc?
Chemically speaking, thiols (also called mercaptans) are a class of organic chemical compounds.
This image shows the basic chemical composition of a thiol group. A ‘thiol’ group means a sulphur atom bound to a hydrogen atom. In comparison to alcohol and phenol groups where a hydrogen atom is bound to an oxygen atom.
So why does it matter?
It just so happens that volatile thiol compounds tend to be very aromatic!
Specific volatile thiol groups are also referred to as ‘varietal thiol compounds’. These varietal thiol compounds have a positive influence on the aroma of the wine. Some of these varietal thiol compounds include:
*OAV meaning odour threshold
Blackcurrant, passionfruit, grapefruit… these tropical aromas are very characteristic of Marlborough Sauvignon blanc, so you would be correct in concluding that Marlborough Sauvignon blanc has higher levels of varietal thiol compounds.
These ‘varietal thiol compounds’ are not present in the grape juice, they are instead present as precursors and are in a non-aromatic form. It is not until the grape juice is fermented that these thiol compounds transform into the volatile thiols, thus revealing their aromatic potential. Even then, not all of these ‘precursors’ become the volatile thiols.
Many studies have been undertaken to determine how to encourage the production of varietal thiol compounds, involving both wine-making and viticulture procedures. For example, the yeast strain plays an important role in the formation of volatile thiol compounds and specific yeasts strains can be purchased which claim to encourage the formation of more fruity thiols.
Not all thiols are desirable
The wine-world jargon can be cause for some confusion. ‘Thiol’ and ‘Mercaptan’ both refer to the class of organic chemical compounds where a sulphur atom is bound to a hydrogen atom. However, thiol usually refers to desirable tropical aromas, wheras mercaptan usually refers to negative vegetal aromas (see image).
It is not fully understood what causes these mercaptans, however it is believed that it is formed during fermentation, involving a reaction between H2S (Hydrogen sulfide) and ethanol/methanol.
Stay tuned…More on this in my next blog-post
References:
Goode, J. (2007). Mercaptans and other volatile sulfur compounds in wine. Wineanorak. https://www.wineanorak.com/mercaptansinwine.htm
Thiols and beyond. (n.d.). Wineanorak. Retrieved December 15, 2020, from https://www.wineanorak.com/thiolsandbeyond.htm
Volatile Sulphides: Detection and Prevention. (2015). ETS Labs. https://www.etslabs.com/library/31#:~:text=Volatile%20sulfur%20compounds%20can%20contribute,effective%20treatment%20and%20prevention%20plan.