Some herbs and spices are used to provide the substance of a dish as well as its aromatic essence. A puree of fresh herbs, as in the Italian pesto sauce made from basil, is thick because the herb’s own moisture is already bound up with various cell materials. And thanks to the abundance of those cell materials—mainly cell walls and membranes—such purees also do a good job of coating oil droplets and so creating a stable, luxurious emulsion. Fresh chillis, which are fruits, produce a watery puree, but one that cooks down to a wonderful smoothness thanks to its abundant cell-wall pectins. Many Mexican sauces are made from a backbone of dried chillis, which are easily rehydrated to produce the same smooth puree; and Hungarian paprikashes are thickened with powdered chillis.