Friday, January 11, 2013

PWVJ: Minerality Rigorous or Romantic?

This article in the Winter 2012 Practical Winery and Vineyard Journal called "Minerality Rigorous or Romantic?" written by Jordan Ross, intrigued me and as I read the article it refreshed my memory of listening to Prof. Carole Meredith's lecture on a DVD that constituted part of the Introduction to Winemaking. The romance here is that the minerality that the taster describes possibly as being "chalk, flint, salty, oil, soil, oyster shell, iodine, or smoky" comes directly from the soil and imparts this to the fruit and ultimately the wine.
The rigor is that while it may seem logical to think that the grapes can express the attributes of the soil from which it grew, Alex Maltman, a geologist at the University of Wales, U.K. and Prof. Carole Meredith agree that plants cannot take up minerals which Gavin Sacks, Assistant Professor of Enology at Cornell defines as "an ordered solid with a well-defined chemical structure". Plants, do, however, take up mineral ions such as sodium, potassium, aluminum, calcium, silicon and oxygen. In fact, grapevines absolutely require these macro- and micronutrients in order to grow and reproduce.
Prof. Sack does say that rocks can in fact give off an odor. This odor was given a name by two Australians, J. Bear and R. G. Thomas in 1964 and is called petrichor. Part of the smell of petrichor comes from a compound called geosmin which is an earthy aroma and flavor. I confess, I am particularly sensitive to tasting geosmin because during the summer months, our water tastes to me like dirt. I think that I am tasting geosmin, a product of cyanobacteria (blue-green algae) and actinobacteria (especially Streptomyces), released when these microbes die.
So, what gives wine it's distinctive minerality? Author Jordan Ross sought out Christophe Rolland, ex-sommelier and Alain Ducasse in Monte Carlo for their thoughts. There is a link between high acidity and minerality. Christophe Rolland explained: Minerality can be fragile, as lees stirring while it can enrich the wine, can lead to loss of some vivid, crisp and pungent character that provides an edge.
High levels of malic acid at harvest will always be a favorable factor for minerality in a wine. Randall Grahm of Bonny Doon Vineyard posited that the disulfide/thiol couple may also produce the minerality characters found in wine. All in all, it was an interesting article to read.
Here is the link to the reprint:MINERALITY Rigorous or Romantic?

1. Wikipedia Entry for Geosmin. All structures were drawn by the freely available drawing program from ACD Labs called ACD/ChemSketch Freeware.

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