The Science Behind Pyrazines: A Master of Wine Explains Photo Degradation

As wine professionals and winemakers, understanding the complex chemistry behind the compounds that give wine its unique flavor profile is essential. Pyrazines are a family of compounds commonly found in wine that contribute to vegetal-like flavors, but did you know that they are sensitive to ultraviolet light? In this video, we'll delve into the science of photodegradation and how exposure to UV light can change the flavor compounds inside grapes. We'll explore the different impacts of UV light exposure in regions with cooler climates like the Willamette Valley, compared to regions with more intense sun exposure like California and Washington State. We'll also take a closer look at how Cabernet Franc, a thicker-skinned grape variety, has inadvertently led to a unique flavor profile in Willamette Valley wines. Join us as we explore the fascinating chemistry behind pyrazines and wine production.

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Thumbnail: "Beautiful Cabernet Franc!" by Hanzell Vineyards is marked with CC BY-ND 2.0.

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Pyrazines are compounds commonly found in wine that contribute to vegetal-like flavors, such as those resembling bell peppers, green beans, jalapenos, and chili peppers. These compounds are sensitive to ultraviolet (UV) light, which can cause photo degradation or changes to the flavor compounds inside grapes. In regions with a cooler climate and a northern latitude like the Willamette Valley, where the hottest part of the day is usually around 5 pm during the summer, there is a significant amount of UV light exposure to the fruit, particularly if there is little shading from surrounding leaves. This exposure can cause degradation of pyrazines, leading to a unique flavor profile in wines.

On the other hand, in regions like California and Washington State, where the sun is too strong and temperatures are too intense, the fruit can easily burn, preventing significant exposure to UV light. As a result, wines from these regions may retain a significant amount of pyrazine compounds and have higher alcohol contents.

The Cabernet Franc produced in the Willamette Valley is a unique example of this process. Because the region experiences significant humidity and disease pressures in the spring, farmers expose the fruit significantly in order to mitigate these threats, inadvertently leading to more UV light exposure and pyrazine degradation. Cabernet Franc's thicker skins, looser cluster morphology, and ability to hang through autumn rain events make it ideal for the Willamette Valley's cool, maritime temperate climate.

This accidental discovery has led to the development of an extraordinary Cabernet Franc flavor profile, which even industry professionals struggle to understand. It highlights the importance of understanding basic principles of chemistry and how they apply to wine production.