Rotundone in Gruner Veltliner and skin contact impact

by Richard B.
(Montreal)

It is also interesting to mention that rotundone, as you mentioned in your article What does Make Peppery Wines Peppery? is variety specific, and is present in the white skin of Gruner Veltliner.

Wine tasters appreciate this varietal characteristic in Gruner Veltliner "the Groovy white peppery wine" as a white pepper taste (rotundone is known to be present in black and white peppercorn).

It is still curious and unexplained that rotundone concentration is kept in winemaking following skin contact since rotundone presence is mainly located in grape skins. White Gruner Veltliner elaboration has very short to no skin contact !?...

References:

Meet Gruner Veltliner Central Europe Sexiest Grape

Manipulating Peppery Wines

Sesquiterpene Rotundone

Image from: Gismondi on wine

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Rotundone in Gruner velltliner wines
by: Roar Lie, Norway

This comment was prompted by Richard B. from Montreal who writes:
«It is still curious and unexplained that rotundone concentration is kept in winemaking following skin contact since rotundone presence is mainly located in grape skins. White Gruner Veltliner elaboration has very short to no skin contact !?...»

This is a relevant and timely question, but short or long skin contact (maceration) in itself is not the only decisive element. We also have to consider timewise how easily rotundone is extracted from the skin (exocarp).
The problem is, however, that such information doesn't seem to be readily available.
The two most important factors in Grüner veltliner (GV) maceration and rotundone extraction are temperature and contact time.
To sum up, it is not necessarily true that «White Gruner Veltliner elaboration has very short to no skin contact». It depends largely on the intended wine style, oenological practices, and decisions, as exemplified in the text below.

The Austrian winemakers I am referring to, use GV maceration for an extended period of time as compared to what is normal in the white winemaking process simply because, in order to obtain GV-wines with a sufficient proportion of rotundone, long maceration times are required. Thus, it may explain why Rotundone is found in high concentrations in Grüner veltliner wines.

Based on experience, personal preferences and winemaking philosophy, they obtain the hallmark of GV wines with its peppery flavour. Besides, winemakers may employ methods they seldom talk about such as thermovinification, usually with temperatures above 60°C, to speed up and increase extraction of certain flavour compounds, and enzymes to cleave chemical bonds.
It should be noted that the use of enzymes in winemaking is strictly regulated in many countries.
Also, the use of flavour enhancing enzymes are met with mixed feelings inside the winemaking community with varying degrees of acceptance.

As an introduction to Grüner veltliner and an explanation of its peppery character, let me start in the winemaking Jura region of France.
In contrast with conventional white wine production, yellow wine or orange wine (fr. Vin jaune), a specialty in this region, the white variety Savagnin is macerated with skin contact for days or weeks. Sometimes even months.
During this period, the winemaker uses pre-fermentative maceration or cold soak which is an interesting winemaking technique to enhance the extraction of pigments, aroma, and flavour components mostly avoiding bitter-tasting phenolics.

From Jura to California; Gewürztraminer (GT) with aromatic compounds concentrated in the grape skins goes through a similar winemaking procedure with extended maceration. It is also interesting to note that the prefix Gewurz in Gewurztraminer means spice or spicy.

According to winemaker Nicole Bertotti Pope of Stolo Family Vineyards & Winery in Cambria, California, she has increased the duration of skin contact over the years for her GT, starting with a few hours, and eventually increasing to 18 hours. She says: [1]
"The longer the contact, the more I liked the result—the more of those compounds are extracted out into the wine".

In Austria where Gruner Veltliner has its spiritual home with approximately 94% of the total world production, many winemakers employ the same technique to release rotundone from the GV-skin and give the wine its typical peppery character.

Let me quote two Austrian winemakers; Bernard Ott, from Weingut (Winery) Ott in Wagram,
Niederösterreich (Lower Austria) and Marion Ebner-Ebenauer, from Weingut Ebner-Ebenauer in Weinviertel, Niederösterreich.
Bernhard Ott with the well-deserved nickname «Mr. Veltliner» is of the fourth generation and has managed the winery since 1993. He says: [2]
"All the grapes and stems are crushed and have skin contact for about 8 to 15 hours before being pressed" .... «I believe that this traditional way of working makes the wines spicier, nervier, and a touch more savory».

It should be noted that not only the grape skin is a rotundone source, it can also be found in stems. This could be the reason why Mr. Veltliner macerates with stems to enhance rotundone extraction.

In Austrias Weinviertel region, Marion Ebner-Ebenauer, another proponent ot Grüner Veltliner makes expressive GV wines with peppery flavour. She says: [2]
«The crushed grapes have 12 to 24 hours of skin contact before they are pressed and fermented with indigenous yeasts».
In both cases, the two Austrian winemakers initially employ pre-fermentative maceration like they do in the Jura region.

For the first time, in 1967, a peppery smelling compound was isolated from the Cyperus rotundus, a tropical perennial plant, which explains the handy trivial name rotundone, being a peppery chemical C15H22O.

According to IUPAC nomenclature of organic chemistry, the correct name is:
(3S,5R,8S)-5-Isopropenyl-3,8-dimethyl-3,4,5,6,7,8-hexahydro-1(2H)-azulenone. (Also mentioned by Isabelle)

Much later (AWRI, 2008) rotundone was verified in Australian Shiraz wines. Not surprisingly, the same compound is found in white and black peppercorns.

Finally, why is rotundone produced in some cultivars and not in others? The question is an intriguing one and the following quote may provide some clues. [3]
"Rotundone belongs to the terpene chemical family, many of which are considered herbivore-induced plant volatiles. It is possible that rotundone or its precursors are produced locally in specific tissues as defensive compounds to protect grapevines from herbivores".

References: 1) Alex Russan:The Science of Terpenes and Isoprenoids, May 25, 2020,
https://daily.sevenfifty.com/the-science-of-terpenes-and-isoprenoids/
2) Anne Krebiehl, MW: Meet Grüner Veltliner, Central Europe’s Sexiest Grape, Wine Enthusiast. https://www.winemag.com/2017/06/07/meet-gruner-veltliner-central-europes-sexiest-grape/
3) Pangzhen Zhang et al. Distribution of Rotundone and Possible Translocation of Related Compounds Amongst Grapevine Tissues in Vitis vinifera L. cv. Shiraz, Frontiers in Plant Science, 2016;7:859.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4914589/

Thank you for this complementary information
by: Isabelle

Thank you Richard for this additional information. The article of Geffroy et al. I quote in my article does not provide any insights on why Rotundone is found in high concentration in a white wine such as Gruner Veltliner. More research is needed.

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