Napa

Napa is an interesting case study because of the fog that rolls in from the San Pablo Bay to create different climactic layers throughout the valley. As you move up from Coombsville to Oakville and finally to Calistoga, temperatures rise, and the phenolic balance of the fruit shifts accordingly.

Coombsville, Oak Knoll: Southern Napa’s climate is perfect for anthocyanin and tannin synthesis, so in a good year, pigment levels of each can reach well over 3000 ppm. This is an extraordinary amount of color, but tannins are also typically abundant (2000-3000 ppm) leading to “lean” wines dominated by astringency. This makes these terroirs a frontier in Napa for talented winemakers who know how to manage tannins using tools like extended hang time, whole berries, smaller porous vessels, cooler fermentations, gentler punchdowns, and shorter macerations to moderate the rapid extraction of tannins.
Yountville, Stag’s Leap, Oakville, Rutherford: Sandwiched in the middle of Napa are also the two AVAs with the most 100-point wines, Oakville and Stags Leap District. While conditions can change significantly from the east to west side of the valley by the heat of the evening sun, in general, these two AVAs have the most natural phenolic balance between color and tannins. Here, Anthocyanins often accumulate over 2000 ppm which tends to coincide near their harvest window. Tannins in the finished wine typically range between 1000-2000 ppm and bound anthocyanins form accordingly, usually around 200-300 ppm. This naturally makes a reserve style that has a lot of structure and concentration but low to moderate astringency. Winemakers here often play with the natural balance of the fruit using techniques like 100F peak fermentation temperatures for 24-72 hours to build stable color early on and create a plush pleasing style, or 85F peak fermentation temperatures that are macerated longer and kept warm post-fermentation to create a refined reserve style.
Saint Helena, Calistoga: Finally, moving up north to Saint Helena and Calistoga, the morning fog dissipates quickly due to its distance from the bay, and therefore temperatures rise. Tannins accumulate and reach their peak before veraison and are more resilient than anthocyanins in response to heat stress, so these wines typically have a lower color-to-tannin ratio and can be more astringent. Pigments often reach 750-1500 ppm at peak accumulation, and tannins may soften from higher temperatures that accelerate their oxidation in the vineyard. The resulting wines may have less flavor and color concentration but vary in structure and astringency depending on practices and the weather in a given year. The higher temperatures will also create a more expressive aroma profile by oxidizing tannins and decreasing their activity. As a result, winemakers will likely push their fruit harder by crushing their berries, using larger stainless steel vessels, pumpovers, warmer fermentations, and longer macerations to increase structure and accelerate the fruit’s naturally slow extraction.

It’s important to note that climate change and extreme weather events are changing the way winemakers think about ripeness and the opportunity cost of hanging their fruit through such an event. With so much on the line, it is important to learn how to adapt winemaking practices when deciding to harvest fruit earlier. For example, controlling the timing and application of variables like temperature, movement, oxidation, additions, and treatments are essential for achieving your desired style. Risk management has always been a part of the conversation in European estates. With so much economic value in the vineyard, it’s no wonder why many estates are reducing the risk of quality loss from extreme weather events (heat, smoke exposure, frost, atmospheric river, etc.).