In Vino Veritas: On Wine, Weather and Climate

Note: this was first published on on March 25, 2014. 

“Give me wine to wash me clean of the weather-stains of cares.” ― Ralph Waldo Emerson

We all watch the weather.

Most of the time, we don’t think about what it means beyond the immediate concerns: do I need an umbrella today? A heavier jacket?

It’s automatic, and it quietly shapes our lives.

Winemakers don’t watch the weather. They live it. It’s the single most important ingredient in the quality and quantity of their product.

In fact, sun, wind and rain are the main inputs into an industry that adds an estimated $162 billion to the national economy annually and provides the equivalent of 1.1 million full-time jobs.

The success or failure of a vintage in any given season is linked directly to the vagaries of ridges and troughs, inversions and heat domes.

As with producers of all our agricultural products, winemakers are affected by weather in a way that most of us can only imagine.

Winemaker Meteorologist

I recently spoke with winemaker James Hall about the impact of weather on wine production. James is a co-founder and chief winemaker at Patz and Hall, one of California’s most highly regarded wineries — with a celebrated portfolio of single-vineyard Chardonnay and Pinot Noir wines.

James is also, for all intents and purposes, a meteorologist. Every day, he thinks about the weather in a more exhaustive and personal way than most forecasters.

Weather is that nagging concern that keeps James awake at night and consumes his daily planning decisions. For James, every decision about the wellbeing of his grapes and the profitability of his vineyard relies on weather.

Quantity is Made in the Spring

As with other crops, the planning for grape season starts long before the grapes are harvested.

Using what are known as Heat Summation Units (HSUs) — an index calculated based on daily average temperatures greater then 50 degrees Fahrenheit — winemakers can estimate when grapes will be ready to harvest based on the date of the bud break and the average accumulation of HSUs for the location.

With those two bits of information, they can estimate when they should harvest the crop and put together a strategy to maximize the quality and quantity of the harvest.

The timing of “bud break” is one of the most important issues to take into consideration when strategizing. If bud break happens early, the crop becomes exposed to the risk of frost damage. Early frost, then, could result in reductions in the eventual yield of the vineyard.

Because of these early risks, winemakers note that grape quantity is determined in the spring.

Playing Poker with the Weather

The weather in the last six weeks of a vintage is the most critical time in the grapes’ lifespan. This is when any careful winemaker watches the weather “like a hawk,” according to James.

During those six weeks, rain on mature crops can cause grape rot, and a late frost can damage the grapes on the vine.

It’s during this phase in the growth cycle that vineyards practice what James calls “playing poker with the weather.” They have to make the choice whether to harvest and take their winnings or to wait for the absolute best conditions and get a higher quality grape. Of course, this waiting leaves grapes vulnerable to the weather’s fluctuations.

To account for this unpredictability, James and many of his colleagues use a commercial weather service (Western Weather Group) to monitor weather conditions both at the macro and micro level: using weather satellites for a larger picture and vineyard-specific sensors for a more granular one.

The meteorological inputs they get from the ground and from satellite sensors and radars all help them make the “hold ‘em or fold ‘em” harvest call.

Ultimately, weather in the spring shapes the quantity of a harvest, but the final month determines the quality of the grapes.

Grape Expectations

Dr. Antonio Busalacchi, a professor at the University of Maryland, is a climate scientist with a twist. He’s also a sommelier.

In a recent article published in Science News, Dr. Busalacchi explains in detail the often surprising impact of climate change on the production and quality of wine. He says, “A number of wine regions around the world are in the sweet spot right now. We have been seeing places like Bordeaux, Germany and northern Italy, even California, putting together a string of very good and very consistent vintages as a result of climate.” (Read the full story here.)

In the case of Napa Valley winemakers, where weather is so much a part of daily decision-making, climate change is a huge concern.

As is typical of the optimistic spirit of American farmers in general, James sees a possible silver lining for California grape quality.

As inland temperatures continue to rise, the marine layer along the California coast will continue to moderate, moisten and cool the key grape growing areas in northern California. These are optimal conditions for the varietals that thrive in that area.

Bailed Out

The drought in California is having a significant impact on the state’s economy and on its large agriculture industry.

After two spectacular years for wine production in 2012 and 2013, this year’s vintage was at significant risk due to the lack of available water for irrigation.

It was touch and go coming out of the winter, and wine producers across California were facing what looked to be a very difficult year.

And then came the Pineapple Express.

The weather pattern changes in early February brought much-needed rainfall to northern Calfornia. According to James, the rains “bailed them out big time.” Now wineries in northern California are optimistic for another great vintage.

In vino veritas indeed!