Methoxyprazines (MP) are a subset of the larger chemical group, Pyrazine, and have been identified by scientists as the chemicals that cause the vegetative qualities in wines. We have been talking about this subject in recent blogs including the Flash Detente blog that is about new technology which eliminates much of it via a steam treatment prior to vinification. Untreated MP results in bellpepper and green bean aromas along with astringency and bitterness in red wines and grassiness in whites. The red types most often affected are the Bordeaux varieties of Cabernet Sauvignon, Merlot, Cabernet Franc, Carmenere, and Malbec; white wines affected are largely Sauvignon Blanc.
In the last blog we discussed a vegetal Malbec from Argentina that was the most popular wine at our last tasting. This conflicts with the prevailing wisdom that vegetal characteristics are a flaw, until we accept that some grape varieties either have MP as part of their varietal flavor or we have developed an acceptance of it as part of, say, the complex Cabernet experience. Also MP has only recently been explored in grapes because at its densest grape concentration, it constitutes just 10-15 parts per trillion.
What seems to happen with grapes in the vineyard is that MP is triggered between fruit set and about two or three weeks before veraison (Blog March 17,2012). Veraison is the onset of grape ripening or the transition from grape growth (cell division) to grape ripening and the change in color from green (chlorophyll) to red or something else (phenollic compounds). Prior to this stage, MP is concentrated in the stem and leaves of the vine but at the point it appears in the berries, it seems to act as a biological deterrent to predators for the survival of the vine before gradually diminishing until harvest time.
One factor that seems to definitely adversely affect grape quality is rain. If it happens during that window before veraison when MP becomes activated in the berries, those grapes will be harvested with a higher MP level. MP, by the way, does not diminish by way of dilution in the growing grapes as you might think but rather it breaks down chemically and sunlight may be a factor here. Thinning the leafy vine canopy and managing vegetative growth in general seems to help.
Two easy methods of reducing MP in grapes are to pick only well-ripened grapes and to let them sit idly for twenty-four hours prior to crushing. No winemaking technique of any kind affects MP because it is entirely due to conditions in the vineyard.
Two recent developments in viticulture deserve mentioning here. Extreme pruning of Cabernet Sauvignon vines to produce highly extracted intense wines may actually have more MP than others unless the vegetation is thinned as stated above to ensure good sunlight. Zinfandel viticulture, by contrast, is now going in the opposite direction with a revival of bush vines which were the norm a hundred years ago. These unpruned vines offer fruit with fresh red and black (jammy) berry aromas and little in vegetal characteristics.
This Friday Tommy Basham of Continental Beverage rejoins us with three from Spain including: Fagus of Coto de Hayas featuring fruit from hundred year old vines, California Zinfandel and Cabernet, and an Italian sweet red. Join us here Friday between 5 and 7pm. For this tasting we are requesting a donation for the Susan G. Komen 3 day-60 miles hike next month in Atlanta. My participant daughters need to raise close to $5,000 for this thing. Any free will donation is appreciated.