Thank you everyone for your responses to last week's topic on Kouloura!
This week: Fog
How can fog impact growing conditions in the vineyard?
In warmer regions fog can protect the vines from over-ripening too soon, allowing the vines to maintain desired acid levels. In cooler places however, it can block sun light necessary to fully ripen, essentially halting photosynthesis. The wind factor in a cooler climate region will lower temperatures even more so where there is fog you hope for lower wind activity.
Also, fog and botrytis (along with all of the unwanted fungi) are bffs!
A classic example of this would be Sauternes. The Sauternes region is South of the Bordeaux city, fringed by the Garonne and the Ciron rivers. The water of Ciron is cooler than that from the Garonne, so during Fall every year when the weather is relatively dry, fog is produced every evening to the next morning when the water from the 2 rivers meet.This is an ideal growing environment for the fungus Botrytis Cinerea which would proliferate until the mid-day sun stops its activity. This daily cycle would repeat itself everyday . And the classic noble rot grapes are the raw materials for the now world famous wine.
In a region such as the Sta. Rita Hills of Santa Barbara, which lies in close proximity to the Pacific Ocean, and has an East-West transverse running mountains, fog, a buffer between grapes and the sunshine can assist the grapes in cooling and acidic respiration.
I find this topic quite interesting. I am propelled to think about one of the most classic viticultural regions, Piedmont, and it's native variety Nebbiolo (stemming from the Piemontese word for fog- nebbia). Nebbiolo is renowned for creating wines of great acidity, mature tannic structure, and complex aromas of earth and spice balanced with that just ripe flavors of red fruit. The relationship of fog in the region for grapes with such potential is a curious one.
After a bit of research I came across this excerpt from a study on sun shading and the Effect of artificial shading on the tannin accumulation and aromatic composition of the Grillo cultivar (Vitis vinifera L.):
"The effects of sun exposure on grape composition are vast and complex. The radiation and heat from sunlight can influence metabolic reaction rates and cause stress, either by dehydration or by a direct increase in temperature. It is generally accepted that shade results in significant alterations in grape composition and reduces wine quality."
My understanding has always been that sugar and pH increase during the maturation of grapes while tannin simply evolves. In regard to tannin evolution, grapes have an innate measure of tannin dependent on varietal and the goal of a grape grower is to harvest when tannins have matured from green tannin flavors and textures. I understand that sugar levels increase due to photosynthesis (direct relationship to visible light rather than UV light), so fog will slow the production of sugar. What about tannin?
If I am able to relate shade to fog, according to this study sugar and color are reduced in shaded grapes while aromatic compounds are increased. However, proanthocyanidins increase which can be related to structural components.
So for the right variety, such as nebbiolo, we can explain why fog can have a beneficial effect on the maturation of tannin over a longer period of time while sugars and skin maturation (color/raisining) do not spike and still have an increase in aromatic complexity. It is interesting to think about how that relates to Sta. Rita Hills Pinot Noir and it's considerable reference points. As well it relates interestingly enough to the color and complexity of some of the most elegant Sauternes even with the botrytis effect.