Vineyard Terroir

Let’s take a look at how climate, soils, viticulture, and winemaking have led to the creation of some of the world’s most renowned vineyards and wines.


Napa Valley is a small area with a big reputation. The whole valley is only 30 miles from north to south and only 5 miles wide. However, in this densely packed valley, we see a lot of diversity in vineyard location, soil type, and climate leading to many different styles of wine, from sparkling white wines to robust, tannic red wines.

How does terroir affect wine?

Terroir ("tear-wah") is a French word that loosely translates into a land's potential to produce agriculture.

Where and how grapes are grown will have a profound impact on what the wine will taste like - giving each wine region a unique wine style.

So, to better understand terroir, let's break it into three categories:

  1. How the climate, soils and geographical features affect wine
  2. The winemaking practices and traditions
  3. Grape growing (aka viticulture)

Together, these three characteristics help explain why certain wines from specific places have this "je ne sais quoi" – an undefinable yet unmistakable taste.

What we've observed in the Napa Valley is substantial diversity in the region's wines from North to South. Here's how the climate and terrain affect the wines.

San Pablo Bay

Vineyards close to the San Pablo Bay produce lighter, elegant wines including Pinot Noir, Chardonnay, and sparkling wines.

Napa has a Mediterranean climate, perfect for grape growing but it isn’t just a very warm and sunny place all the time. Thankfully, as is needed to grow high-quality grapes, there are some cooling influences throughout the valley.

San Pablo Bay, an extension of San Francisco Bay and the Pacific Ocean, a cold body of water, brings cool air and humidity to those vineyards in the southern part of the valley, such as AVAs like Los Carneros and parts of Coombsville and Wild Horse Valley. These cooler temperatures are perfect for grapes like Pinot Noir and Chardonnay. It’s so cool that we even see sparkling wine being produced!

In the evening, fog can form and be funneled up through the valley, creating a blanket over the vineyards. This drops the temperature and also shields the valley floor vineyards from the morning sun - slowing ripening and helping create more complex flavors.

Valley Floor

Valley vineyards deliver ripe, lush, and full-bodied red and white wines

The further up the valley the less fog and cool breezes we see, and therefore it’s warmer. This is where we start to see more Cabernet Sauvignon and Merlot planted. This extra warmth and sunshine create fuller-bodied and riper styles of wine. We can see these riper and full-bodied Merlots and Cabernets in valley floor AVAs like Rutherford, Oakville, and Stags Leap District.

Mountains

Mountain vineyards in Napa Valley make robust-yet-restrained red wines with high tannins and minerality.

On either side of the valley floor are a set of mountain ranges that help define Napa Valley, the Mayacamas Range on the western edge of the valley, and the Vaca Range on the eastern edge.

The Mayacamas Mountains protect Napa from the cold Pacific ocean and face east, receiving the morning sun. The Vaca Mountains protect from the very warm and arid Central Valley, and face west, towards the afternoon sun, which is a bit warmer.

Not only do these mountains help define Napa Valley and funnel in the fog and cool breezes from San Pablo Bay, but they also allow growers to plant vines at elevation. With every additional 100m (328 ft) in elevation the temperature drops by 0.6°C (1°F). With elevations upwards of 2600 ft (that's nearly 8°F / 5°C!) it means it's cooler. This leads to wines that aren’t as ripe and juicy, and a bit more restrained.

If vines are planted above 1600 ft then they are above the fog line, which means they see more sunshine than the grapes planted on the valley floor. So even though it’s cooler in the mountain AVAs like Howell Mountain, Mount Veeder, or Atlas Peak it might be sunnier than the valley floor AVAs. This means that we can still ripen the grapes perfectly though they tend to be a bit more tannic and grippy compared to the lush, full-bodied examples at lower elevations.

Northern Napa Valley

The cool nighttime temperatures make wines which are both ripe and robust with fresh acid and lots of tannin.

Northern vineyards in Napa Valley like Calistoga and Diamond Mountain District cool down at night. This slows down the ripening to create very full-bodied, intense wines, but with balanced levels of fresh acid.

The cooling influence comes from the Chalk Hill Gap. This should be the hottest spot in Napa because it’s the furthest away from San Pablo Bay. However, the break in the Mayacamas Mountains lets cool air from the Pacific Ocean to flow in at night.

Napa Valley Soils

We wish we could tell you that Napa has one or two soil types to make things easy, however it contains 50% of the world’s soil orders! There are volcanic soils, marine bedrock, and sedimentary soils, all mixed together due to some crazy geological activity about 150 million years ago.

This is a geologist’s playground and so it can be hard to identify vineyards by soil type. So instead, lets break down the soil conditions into mountain soils, valley soils, and fluvial (riverside) soils.

Soils are thinner in the mountains, such as Lail Vineyards on Howell Mountain
Mountain vineyard soils

Expect high tannin, structured, and complex wines that are best for cellaring for a number of years.

Erosion in the mountain AVAs, like Diamond Mountain District and Mount Veeder,/mount-veeder results in thin soils, poor in nutrients - this causes the vines to struggle. Cabernet can do well on these soils and the berries are small and intense, creating very tannic wines that are structured and complex. Check out Cabernet Sauvignon, Zinfandel, and even Malbec from the mountains.

If you look closely, you can see how Conn Creek Winery sits on an alluvial fan in Rutherford.
Vineyards on alluvial fans and bench vineyards

Fruit forward and slightly less tannin than those found in the mountain vineyards, but still meant for cellaring.

Soils are eroded and fall down the mountains where rocks, stones, and smaller pebbles are deposited. Many of the nutrients from the mountainside are also deposited here at the base of the mountains. These are called alluvial fans and are deep, well-drained stony soils that are moderately fertile. These are also known as Benches in Napa Valley, one of which can be found in Rutherford AVA. They sit at the base of the mountains on both sides of the valley. These are where some of the most expensive and award-winning Cabernet Sauvignon Blends are found.

The vineyards at Opus One Winery butt up against the Napa River.
Vineyards next to the river (aka "fluvial vineyards")

Lush, full-bodied, and fruit-forward wines. A great spot for white wine growing in Napa Valley

These soils are made mostly of silt and clay that has been washed down from the mountains over time. They are nutrient-rich soils that retain water well - vines planted on these soils might not need irrigation. The resulting style is rich, ripe, and fruity. Check out Cabernet Sauvignon, Sauvignon Blanc, Sémillon, Merlot, and Petit Verdot from these areas.

This chart uses the system for identifying wine climates that Dr. Gregory Jones invented.

Climate

The climate in Napa is Mediterranean – only 2% of the world can say this. This is an ideal climate for grape growing.

A Mediterrean climate means most of the rain falls during the winter months, and in Napa, it's about 27 inches (685 mm) a year. This means that many vineyards need to be irrigated, though some producers are trying dry farming, especially with older vines whose roots have access to deeper water reserves.

Due to the lack of water, and several recent droughts, availability of water is becoming an increasingly important issue. The area also had several wildfires close to it, which can affect the quality of the grapes, cause destruction of the winery itself and, very sadly, loss of life.

What else makes wines taste the way they do?

Geographical features, climate, and soils all play a major role in terroir, however people are needed in order to produce great wines from these areas. Join us in looking at how viticulture and winemaking play a critical role in terroir.