Last month we discussed how our calcium-carbonate rich (CaCO3) soils provide innumerable benefits here at Apu Winery. We would like to explore this subject more, focusing on how the pH and nutrients of our limestone soils affect the acidity (and therefore the general flavor and quality) of our Peruvian high-altitude wine.
Our soils have a pH between 7.8 and 8, which means they are moderately alkaline. Alkaline soils, especially calcareous alkaline soils, tend to produce grapes with higher acidity. As Jon Iverson states in "Home Winemaking Step by Step", most grapes should have a pH between 3.2 and 3.4 (35) when picked. With the assistance of our soils, our grapes easily reach the desired pH before harvest. For example, last October, at peak ripeness, our 2018 Sangiovese grapes measured a pH of 3.32. We can thank the crumbly layers of earth that provide a habitat for our roots and vines for this.
Calcareous soils cause acidity in grapes and wine in a couple of ways. First, calcareous soils don’t retain heat and therefore have lower temperatures than other types of soils. Because of this cooler temperature, the grapes ripen more slowly, allowing them to develop perfect ratios of sugar and acidity. Second, calcareous soils are high in calcium but low in other nutrients such as potassium. It has been shown that the combination of low potassium and high calcium produces grapes and wines with optimum acidity (Tablas).
Calcareous soils not only lack potassium, but also tend to lack nitrogen, phosphorous, zinc and iron (Management). We add these nutrients to our drip irrigation system to ensure the plants get what they need to produce healthy, robust grapes for our high altitude wine.
Iverson, Jon. Home Winemaking, Step-by-Step: a Guide to Fermenting Wine Grapes. Stonemark Pub. Co., 2009.
“Management of Calcareous Soils.” Calcareous Soils | FAO SOILS PORTAL | Food and Agriculture Organization of the United Nations, www.fao.org/soils-portal/soil-management/management-of-some-problem-soils/calcareous-soils/en/.
“Why Limestone Matters for Wine Grape Growing.” Tablas Creek Vineyard Blog, 26 May 2010, tablascreek.typepad.com/tablas/2010/05/why-limestone-matters-for-viticulture.html.