Chalk plays a crucial role in the vineyard, offering benefits that can elevate a wine’s quality, but in excess, it can be fatal for vines.
Champagne rests on a bed of chalk that’s 300 meters thick. Across the English Channel, growers often plant Champagne grapes on similar chalk formations. There’s even chalk in Texas, where American rootstocks were found to be compatible with the alkaline soils of Champagne. Chalk is a type of limestone, though not all limestone is chalk. For example, Saint-Émilion has limestone but no chalk. While limestone is hard and durable, making it suitable for construction, chalk is soft and easier to dig, as evidenced by the tunneled cellars under Epernay. So, what exactly is the difference between chalk and limestone, and how can both be beneficial and detrimental to vines?
Understanding Limestone
All limestone is a sedimentary rock composed of ancient marine organisms, but it varies significantly in structure and chemistry. In Burgundy alone, there are multiple types: crinoidal limestone in Chambertin, dalle nacrée in Pommard, and Oxfordian limestone in Saint-Romain. Chablis has its own unique limestone types—soft Kimmeridgian and hard Portlandian.
Even chalk, a specific limestone formed from coccoliths, comes in nine different formations. Ian Kellett of Hambledon values the Newhaven Chalk Formation for its structure, considering it superior for vines compared to other formations like Tarrant or Seaford. Discussing chalk with growers can open up a world of nuanced differences and comparisons, similar to how parents boast about their children’s achievements.
The “active lime” content in soils, which refers to the level of calcium oxide that has weathered out, is another point of pride among growers. In the Marne Valley, about 20% active chalk is common, and calcium plays a crucial role in affecting the acidity of the soil.
Chalk’s Role in the Vineyard
Chalk is ideal for grapes because of its water-handling properties. It drains well, preventing waterlogging while maintaining a consistent water table. Kellett explains that chalk’s capillary action, combined with the plant’s natural processes, creates an effective system that can reach deep into the earth. A cubic meter of chalk can hold 660 liters of water, thanks to the tiny fractures that have formed over millennia.
However, vines planted in pure chalk will eventually die from chlorosis, an iron deficiency that causes leaves to yellow and wither. Effective chalk soils have some iron content as well—Champagne’s lignite coal and Sancerre’s weathered sandstone layers provide the necessary iron. Even in Champagne, chalk requires some clay to be beneficial.
The composition of topsoil doesn’t just come from the underlying rock; it also includes materials washed or blown there over time. These processes introduce essential minerals, including iron, though it must be in a soluble form for vines to absorb it.
Impact on Wine Style
Chalk and limestone soils are often associated with wines that have freshness and elegance, thanks to their excellent drainage and water retention. These soils warm up faster in spring but reflect more heat, which influences wine style. Alex Maltman notes that the reflected light’s wavelength, which depends on soil color, can affect enzyme activity and ultimately the wine’s sugar and alcohol content.
In Burgundy, the classic soil type is argilo-calcaire, a mix of clay and limestone. It’s said that darker, clay-rich soils suit red grapes, while lighter, limestone-rich soils are better for white grapes.
Limestone soils tend to produce wines with lighter tannins, brighter aromas, and a generally brisker profile. These wines may be lean in their youth but age gracefully. High-calcium, low-potassium soils seem to improve nutrient uptake by the vine, while enhancing acidity. In regions like England, where sparkling wines are grown on various soils, there’s a growing belief that chalk imparts a unique finesse to acidity, making it more perceptible and elegant.
Beyond Burgundy
Château Ausone, known for its elegant Bordeaux, is situated on Saint-Émilion’s limestone plateau. Here, the limestone supports Cabernet Franc and a more restrained Merlot, while Cabernet Sauvignon struggles to ripen. On the opposite side of the river, limestone lies much deeper beneath the gravel, potentially too far down to have a significant impact.
Limestone soils are also found in other wine regions around the world, contributing to the elegance of wines from Cognac, Spain’s Jerez, Slovenia’s karst limestone, and parts of California’s Central Coast. Even in regions without natural limestone, like Rías Baixas in northern Spain, growers supplement their soils with clam shells to mimic the benefits of limestone.
In summary, while chalk and limestone are prized for their contributions to wine quality, they must be balanced with other soil components to avoid adverse effects. The right combination of minerals and soil conditions can lead to wines of exceptional elegance and complexity.
