What are the best soils for wine grapes? This is a frequent topic of discussion while out tasting wine; so much so that displays of rocks, gravel and soils are common in tasting rooms and at wine events.
Soil directly and indisputably affects the wine produced from a given region. In addition to climate and aspect, soil is part of what makes a region’s terroir and can separate mediocre from exceptional wines.
One of the most important viticultural considerations when planting grapevines is the soil composition of the site. The soil is what supports the plant’s root structure, influencing available water levels and amount of minerals and nutrients the vine is exposed to.
The ideal soil condition for grapevines is a layer of thin topsoil and subsoil that sufficiently retains water but also has good drainage so the roots do not become overly saturated. The ability of the soil to retain heat and/or reflect it back up to the vine is also an important consideration affecting the ripening of the grapes.
In the Yakima Valley, a series of cataclysmic events occurring between 18,000 and 15 million years ago left behind a variety of the most desirable soils for growing wine grapes. Volcanoes and lava flows created a bedrock of basalt throughout the Valley. These were then uplifted to form the hills and ridgelines where many vineyards are found today. Waters from the Missoula floods came up into the Valley, depositing sediments on the valley floor.
The surface layers of vineyard soils within the Yakima Valley AVA are based primarily in loess soils. These consist mostly of wind-deposited silt and fine sand derived from sediments from the ice age floods. Wines from these soils are typically very aromatic with smooth tannins.
Most of the soils in the Valley are classified as either silt loams or fine sandy loams, which means they have a low clay percentage relative to silt and sand. The low clay content creates well-drained soils, encouraging the vines to root more deeply, a factor associated with high-quality grapes and wines. It also creates an inhospitable environment for phylloxera, an aphid-like pest that feeds on the roots of grapevines. Due in large part to the clay-poor soils, the Yakima Valley is one of the few places on Earth where European wine grapes like cabernet sauvignon can be grown on their own roots.
The end result is grapes and then wines that are completely true to their varietal character.
The shallow parts of Yakima Valley soil profiles contain calcium carbonate horizons called caliche. In most areas, the caliche forms a conspicuous white layer in the soil that adds mineral complexity.
The deep roots of grapevines often penetrate through the surface layer of loess, which averages 3 feet in thickness, and into the ground below. Depending on location, the substrate below the loess varies dramatically, adding diversity to the Valley’s many terroirs.
When talking to a winemaker who uses Yakima Valley grapes, he or she will note the soil difference from block to block or vineyard to vineyard. These differences are notable in the flavor profiles they produce, offering that special sense of place of Yakima Valley wines.
The following wines are great examples of a varietal true to its character:
■ AntoLin Cellars Yakima Valley 2015 Malbec, $30.25.
■ JB Neufeld 2016 Yakima Valley Cabernet Sauvignon, $35.
Soils are a basic learning topic for wine study. Many Yakima Valley wineries are open during winter months. Off-season touring allows more time to taste, talk and learn. Visit wineyakimavalley.org to see each winery’s winter hours.
• Barbara Glover is executive director of Wine Yakima Valley, an industry group representing member wineries.