The question of “shaken,” rather than “stirred,” is one commonly debated among James Bond fans.
To this, The Ultimate James Bond Fan Book (2006), by Deborah Lipp, provides researched answers in a section appropriately titled, “Shaken? Stirred?”
Why does James Bond always ask for a martini ‘shaken, not stirred’? This is a simple explanation, meant for those who don’t wish to be liquor connoisseurs.
A martini is made with gin and vermouth. Gin can be ‘bruised’ by shaking, which is to say, shaking ruins the taste….
However, James Bond doesn’t drink regular martinis, he drinks vodka martinis. Vodka tastes best when very cold, and the best way to get it to the proper temperature is to shake it up with the ice.
Bartenders, though, are inclined not to shake martinis, because they are accustomed to martinis made with gin.
As Lipp concludes: “Well, now you know.”