There are two reasons we shake and stir drinks: to lower their temperature and to dilute them with water. Both shaking and stirring accomplish this, but each technique is better suited to different types of cocktails. Here’s the easy way to remember when to do what:
Stir a drink that is all liquor. Shake a drink that isn’t.
Cocktails that include non-alcoholic additions (like egg whites, juices, creams, etc.) should be shaken. Shaking gives cocktails a touch of effervescence by forcing tiny air bubbles into them. These bubbles aerate the drink, which allows ingredients with different viscosity (such as egg white and gin) to mingle smoothly. An aerated drink feels light and fresh, and should have a floating layer of miniscule ice chips and bubbles when first poured.
Drinks that require egg whites (like a Violette Fizz) are prone to over-dilution; egg white needs to be shaken longer than juice for it to properly aerate, which can allow too much ice to melt,causing the drink’s flavor to thin. Because of this, it’s best to first dry shake an egg white (shake it alone…or with a small portion of drink’s ingredient…in an empty cocktail shaker), then add the remaining ingredients, and then shake with ice. The dry shake lets the egg emulsify before ice is added, so ice only serves to further chill/aerate the cocktail, and leaves no opportunity for over-dilution.
Drinks that are pure liquor need to feel velvety on the tongue, so they should be stirred to chill them. Ice should be added to a glass full of ingredients, and a spoon should be quickly stirred in the drink to chill it, dilute it, but avoid creating aerating bubbles.
NOTE: This is the traditional rule. Some (including the character of James Bond) prefer their all-booze cocktails to be “shaken, not stirred.” And even I tend to have different preferences based on which drink I’m making, like a Greenpoint. But, if you prefer drinks one way, be sure to tell your bartender, as a quality bar will default to the traditional styles.
Rolling a drink may be a Cocktail Explorer original method, but it seems SO obvious that I can’t imagine it actually is. Rolling is using a capped-shaker (aka traditional shaker, cobbler shaker, etc.) to get stirring results. Add the ingredients to the shaker, slide in ice and/or stainless steel whiskey cubes, lay the shaker at a 45 degree angle in one hand, and use the other to twist the bottom, rolling the shaker until it’s cold. I like it because it allows me to use one tool (a shaker) to make any type of cocktail at social gatherings, cuts down on clean-up time (no spoon or extra glass), and seems to dilute less than stirring.
Swizzling is using a bar spoon to mix ingredients (bitters or mint, usually) in a drink built in layers inside a glass. Insert the spoon to the layer that needs mixing, and roll the coil of the spoon between your hands in alternating directions. It’s easy…it just sounds and looks fancy.
Use a quality blender that is made to be used with ice, and while there is technically no excuse for blending a classic-style cocktail, one could be forgiven for blending rum or tequila drinks if you have insisting guests. Just don’t use pre-made mixes. Ever.