Aroma Compounds
/Minerality
Have you ever heard anyone tell you that a wine smells like a wet stone? What about some nice chalk like notes? These scents come from a variety of elements involved in the creation of the wine. A cool climate Terroir consisting of limestone, and granite soils containing sulfur is generally reasoned to be the source of minerality in wine, but experts aren't so sure that's the final answer. Grape vines consist of over a dozen essential mineral nutrients as a part of their growth cycle, but in tests done using gas chromatography have determined that any single mineral makes up less than .03% of the wine and is far too small of an amount for us to taste or smell. It's more likely what we are experiencing is the scent of Petrichor, or the smell we commonly think of as fresh rain on rocks.
Petrichor
The term was coined in 1964 by two CSIRO researchers, Isabel Joy Bear (Australian) and Roderick G. Thomas (British), for an article in the journal Nature. In the article, the authors describe how the smell derives from an oil exuded by certain plants during dry periods, whereupon it is absorbed by clay-based soils and rocks. During rain, the oil is released into the air along with another compound, geosmin, a metabolic by-product of certain Actinobacteria, which is emitted by wet soil, producing the distinctive scent - Bear, Isabel Joy; Thomas, Roderick G. (March 1964). "Nature of argillaceous odour".
The Results
When you smell minerality or wet rocks in your wine you are smelling the remaining traces of organic compounds that were on the vines when the grapes were crushed that is native to the terroir where they were grown. These organic compounds are highlighted by acidity which is more easily retained in wines grown in cooler climates with a large diurnal cycle. So the next time you take a whiff of your favorite cool climate chardonnay and smell the acid and hints of flint and chalk, take a moment and cheers to the terroir and the scent of Petrichor!