Gravel or clay: how soil picks the grape

Why gravel suits a late grape

Gravel is a heap of stones the rivers carried down from the Pyrenees and the Massif Central over 2 million years. Water goes straight through it, so the vine has to root deep and is never comfortable, which is what a grower wants. The stones warm quickly, and some growers credit them with giving heat back at night. What the research stresses is the drainage, which keeps the vine short of water and pushes it to ripen.

That is the soil for Cabernet Sauvignon (opens in a new tab), which buds late, ripens last, and makes a hard, green wine if it does not get there.

Clay does the opposite. It holds water, warms slowly and stays cool in summer, which slows the vine down and keeps it supplied in a drought. Merlot (opens in a new tab) flowers early and ripens 2 weeks before Cabernet, so it can finish on cold soil where Cabernet would not.

Almost no estate sits on one soil

Almost no estate sits on a single soil, and the good ones plant to the map. At La Fleur-Pétrus (opens in a new tab), on the Pomerol (opens in a new tab) plateau, some parcels are gravel and others deep clay, all on an iron-rich subsoil. The house reads them differently: elegance from the gravel, density from the clay. The vineyard is 91% Merlot.

At Latour (opens in a new tab), in Pauillac (opens in a new tab), the walled heart called L’Enclos (opens in a new tab) is clayey gravel at the center, gravelly sand at the edges, and marly clay beneath. Across the estate Cabernet Sauvignon is about 3 vines in 4; in the grand vin, the estate’s first wine, drawn only from the old vines of L’Enclos, it passes 90%. Cheval Blanc (opens in a new tab), on the Saint-Émilion (opens in a new tab) side of the Pomerol line, farms 42 hectares in 56 plots on 3 main soils. Fifty-six plots is 56 decisions about which grape goes where.

Limestone is the third soil. At the center of Saint-Émilion lies a plateau of starfish limestone under a thin, well-drained topsoil, and growers credit the rock with holding water for the vine through a dry summer. The appellation’s rulebook says it plainly: Cabernet Franc (opens in a new tab) is preferred on limestone soils, Merlot on the cool, moist clays. The terroir pages show the 3 soils in section, and Saint-Émilion and Pauillac set limestone beside gravel.

What each grape brings to the blend

	Cabernet Sauvignon	Merlot
In the vineyard	Buds and ripens late, thick skins, small berries	Buds and ripens early, thinner skins, bigger berries
In the glass	Cassis, cedar, graphite, firm tannin, length	Plum, fig, flesh, softer tannin, earlier appeal
Risk	Does not ripen in a cold year	Ripens too fast in a hot one, and can lose its acid
Job in the blend	The frame	The flesh that fills it

Cabernet Franc is the third voice: earlier than Cabernet Sauvignon, more aromatic, and able to taste green on soil that does not suit it. On the Right Bank it can lead, and Cheval Blanc is 55% Cabernet Franc. Petit Verdot (opens in a new tab), Malbec (opens in a new tab), and Carmenère (opens in a new tab) are seasoning, used in small shares by estates that have somewhere to put them.

The blend is a soil map

The blend is not a recipe; it is a reading of the soil map. When an estate plants 70% Cabernet Sauvignon, it is telling you what is under the vines.