Martinis last month we delicately stirred on ice to control how much water diluted the drink. Our goal with sours on the other hand is not just to chill and lightly dilute it with water, but to aerate it so we get that nice frothy cold foam on top. Ideally you’ll want some type of tin shaker, because the metal will chill from the ice and in turn help chill your drink with less water melting in it.