The Italian puree of basil leaves, pesto genovese, also contains olive oil and so is partly an emulsion as well. Pesto takes its name from the same root that gives us pestle, and the basil leaves and garlic were traditionally ground with a pestle and mortar. Because this takes some time and effort, modern cooks usually prepare pesto in a blender or food processor. The choice of appliance and how it’s used influence both consistency and flavor. The crushing and shearing action of the pestle, the shearing action of the blender, and the slicing action of the processor all produce different proportions of intact and broken cells. The more thoroughly the cells are broken, the more their contents are exposed to each other and to the air, and the more their flavor evolves. A coarse pesto will have a flavor most like the flavor of fresh basil leaves.