Many bartenders beg to differ with the legendary cinematic request by James Bond that his medium dry Martini be "shaken, not stirred." Putting Hollywood aside, the difference between shaking and stirring a cocktail largely comes down to personal preference. There are, however, some real differences that may help you choose between the two styles.
Shaking a cocktail in a shiny, silver bullet-shaped vessel creates a mini-exhibition in a bar or at home with friends, making it a popular way to create and serve martinis and Manhattans. If your goal is to make drinks a little less potent, this is the way to go. Shaking a martini causes some of the ice to break up and dissolve into the drink, diluting the contents. Consequently, less alcohol is poured into the cocktail glass, especially if the bartender tips the remaining slush from the steel shaker into the glass. An experiment by Gizmodo came to the conclusion that shaking ice and alcohol can cut a spirit's potency nearly in half, diluting the drink 1.75 times more than stirring it does.
In an interview with NPR, George Christou of the University of Florida explained that shaking a martini helps remove volatile organic compounds from the alcohol, while air oxidizes other organic compounds that are present, which affects the taste of the drink. Christou compares the effect to letting red wine breathe before you serve it. In addition, less-expensive vodkas made from potatoes contain traces of oil, which are minimized with shaking. The oily flavor is reduced when an emulsion is created from the shaking process.
For ice-cold martinis, shaking is the way to go. Ask the bartender to shake it for only 10 seconds to reduce the melting effect caused by over-shaking the concoction. To keep it cold even longer, add a few small chips of ice to the finished product. If you feel cheated by the lower alcohol content, ask for a larger glass and an extra 1/2 shot of vodka or gin. When making martinis at home, place glasses in the freezer for a couple of hours to help drinks stay cold longer. Crushed ice melts more quickly, so use cubed ice when shaking your cocktails.
Purists stick to a stirred martini to avoid clouding or diluting the alcohol, particularly with premium brands. However, shaking is preferred for blended drinks containing fruit, juice, cream or mixers. Using an electric blender or stainless steel shaker allows air bubbles to form in the mixture, creating the desired frothy effect for showcase drinks like daiquiris and mai-tais. Drinks with carbonated soda are best served without stirring or shaking; ask instead for the cocktail to be "built" by pouring ingredients on top of one another into the glass, then adding ice if desired.