Terroir - Climate and Weather

Climate and Weather

We look at climate and weather in terms of wind, rain, sun, fog, and humidity, but climate and weather are two different things. Climate is the characteristic weather conditions of a region considered over a long time frame. We're talking decades! Weather is what happens from day to day or over a single vintage. Mark Twain explained it very well, "Climate is what we expect; weather is what we get.”
We can look at climate and weather at different scales. We can describe the climate of a large region like California, or climate within an appellation, or microclimate from one vineyard site to another. The viticulturist looks at an extremely precise microclimate which exists within the fruit zone of his vineyard’s vine canopy. What actually happens in these regions in the long term is climate, what happens in a vintage is weather.

While all aspects of weather and climate pertain to terroir and contribute to the vigor and health of a grape vine, the most important influence on terroir is temperature. I discussed the importance of rain and irrigation in the previous post on soil. Climate factors like wind, rain, sun, and humidity, directly affect a vines soil moisture requirements and moisture levels in soil. But their other big effect is on temperature.

The things we taste and smell in wine and which we call terroir are created in biochemical processes during the development and ripening of the grape. These processes are the strongly influenced by temperature. Each individual process in grape development has an optimum temperature where it proceeds the fastest. Above or below that optimum temperature the process goes slower. But it isn’t as simple as whether faster or slower is better.

In a vineyard when grapes are ripening, two things are happening:
1) sugar is being produced in the leaves, transported to the berries, and is accumulating
2) flavors, elements of aroma and taste, are developing in the berry.

Ripening is a race between the two where you want them tied at the end of the race.
The ripening regarding sugar accumulation is pretty straight forward. Sugar is being made and stored until the berry has a level of 24 to 26 Brix. At that point there is a programmed, physiological process where the berry shuts down and begins to dehydrate and collapse. In the warm, sunny regions of California sugar can accumulate rapidly and present a difficulty to the winemaker.

The ripening regarding flavor is less straight forward. Some flavors are produced and increase during ripening like varietal and desirable aromas and soft tannins, other flavors diminish like acidity, bitterness and vegetal aromas. In ideal ripening this flavor development happens before the berry gets too high in sugar or shuts down.
The issue here is that we need the two processes to coincide exactly. Otherwise we can have immature flavors or excessive sugar and overripe flavors in the grape.

So that means we want warm sunny days and cool nights, right? Isn’t that what we always hear? If you go around the world and look at the climates in the greatest growing regions you are struck by the fact that the best regions have warm, not hot, days and relatively warm nights. If you look at Bordeaux or Burgundy, the difference between day and nighttime temperatures is about 20° F. The two regions are different; Burgundy overall is a little cooler and benefits from a different exposure and altitude. But in both regions the nights are relatively warm.

So why do we hear about cool nights so often? It is because grapes ripen both during the day and at night. In regions that have hot nights, grapes ripen quickly with low acid, poor color, and reduced flavor development. This makes for wine of ordinary quality. Grapes are better for wine when ripening metabolism is slowed by cool nighttime temperatures. This allows for slow ripening, more flavor development, and promotes a good sugar acid balance. But you can have too much of a good thing. Nighttime temperature can get too cool and stop the maturation process.

Optimally, we want ripening and flavor development to happen at night as well. We want warm, comfortable days where sugar can accumulate, but at a pace that it doesn’t get to far ahead of flavor development. We want moderate night temperatures so that flavor development can continue and catch up. In this way we have a chance for the race between sugar accumulation and flavor development to be side by side.

Another thing that is important to the vine in the best growing regions is the day-to-day variability in temperature. The better growing regions have a more consistent temperature pattern. Grapevines acclimate to their surrounding temperature and vines don’t like abrupt heat waves or cold spells that disturb the processes of fruit development. An abrupt heat wave can damage leaves, fruit and stun the vine.

Weather defines the vintage.
Weather does not define terroir, but it certainly affects the way a wine tastes. In a given vintage you can have frosts, heat spells, precipitation during fruit set or harvest, and other inclement weather that defines a vintage. But it doesn’t define the region or the terror of that region. Looking at a single vintage it is hard to see the terroir of a region, but vintages seen over an extended time reveal terroir.

I have posted five times now on the subject of terroir and I still haven’t said much about what this all means for Spring Mountain. Well, that’s what Touch the Terroir is all about and I want to hear what Ron Rosenbrand and Ashley Anderson have to say when they take us into the vineyard. So Terroir - On Spring Mountain will have to wait until after the week long harvest experience of Touch the Terroir 2009.

Meanwhile, I would love to hear anyones comments on this subject.

(photos from the top down all from the Spring Mountain District - First snow at Paloma in the winter, Springtime rain clouds over Behrens Family Winery, Summer morning at Vineyard 7&8, and sunrise as seen from Terra Valentine )