What I love most about an Old Fashioned is it's simplicity and adaptability. An Old Fashioned is spirit, sugar, and bitters - a drink served in "the old fashioned way". If you're curious about the origins of an Old Fashioned, read this short article.
Because of it's simplicity, this drink is all about balance and each of the three ingredients plays a large part. It is very easy to make an Old Fashioned too sweet or two strong. Most folks are gentle enough with the bitters that it is rarely too much bitters, but that too can be where things go wrong.
Ice/Water Is Your Friend
An Old Fashioned needs water to open up both the alcohol and the bitters so that neither is too astringent. When you are stirring with ice you are not only mixing and chilling you are diluting the drink. Don't be afraid to let it sit on ice for a few minutes, you will not water the drink down too much, in fact you'll likely make it better. If you find upon first sip that it tastes sharp or burning, you should let it sit a bit longer and give it another good stir before adding more sugar or declaring it a bad drink.
The Right Amount of Sugar, For You
The other common mistake made with an Old Fashioned is using too much or too little sugar. While "the right amount" is different for everyone, I suggest starting with less than you think and making sure you've got enough dilution before you decide to add more. I find more often than not, folks add too much sugar rather than too little. An Old Fashioned should not be a sweet drink, but the sugar should help to round out the sharpness of the alcohol and also work as a seasoning to bring out the flavor of both the alcohol and the bitters.
Also take note that depending on what you use as sugar, maybe maple syrup, demerara syrup, brown sugar, etc, you may use different amounts because they have different levels of sweetness. I find that about a teaspoon is a good place to start, you can always add a bit more.
Bitters Are Your Spice Rack
I use this analogy all the time. Bitters are the spice rack for your cocktails. You can choose a bitters that brings out the flavors already in the drink or a bitters that adds something new and complimentary. I have heard some folks say that the only correct bitters to use for an Old Fashioned is Angostura, but I say they're being too narrow minded. That's like saying you can only season a chicken breast with salt and pepper. What about pesto or lime and chili or bbq sauce? It all depends on what you like and what you want at that time.
Sometimes I want a rich, comforting Old Fashioned so I use a little brown sugar syrup and Dead Guy Chicory Bitters to get a bit of coffee and cocoa flavors in my drink and I might even garnish it with a cocktail cherry. Other times I want the classic and I use white sugar and Old Fashioned Aromatic Bitters and garnish with a twist of orange. And sometime still I want something a little lighter and brighter and I use a few dashes each of Orange Bitters and Cardamom Bitters.
Fun Riffs On A Classic
The Old Fashioned's simplicity lends itself to almost endless experimentation. Here are a few riffs that may inspire your own favorite combination. Remember to adjust any of the amounts to your liking.
Rum Old Fashioned
1.5 oz aged rum
tsp maple syrup
4 dashes Orange Bitters
Mezcal Old Fashioned
1.5 oz mezcal
1 tsp demerara syrup
4 dashes Cardamom Bitters
Tequila Old Fashioned
1.5 oz reposado tequila
1 tsp agave
4 dashes Lime Coriander Bitters
Garden Old Fashioned
1 oz gin
.5 oz dry vermouth
1 tsp rosemary simple syrup
4 dashes Grapefruit Bitters