The idea of a sweet and sour mix is simply one of efficiency in a fast-paced work environment, such as a bar or a big party. By premixing simple syrup and freshly squeezed citrus juice, and then bottling the mixture, you can avoid doing this task repetitively for each drink. For most people, making sour mix is not something they need to do unless they are serving a lot of cocktails at a party. The only other reason to make a batch is to experiment. The best method for the aspiring mixologist is to make it using equal parts citrus juice and simple syrup (2:1). For the professional, there is a recipe that follows that can help with efficiency and still taste great. If you want the whole in-depth story on Sweet and Sour Mix, purchase a copy of Mixologist: The Journal of the American Cocktail, where I wrote a lengthy research-based article.
If you work in a bar, the following recipe is good for two reasons; first, it tastes way better than anything you could buy that is commercially produced. Second, it is cost effective. For one litre of this “bar sour,” the cost is approximately $2.50 per litre or less. Finest Call premixed bar sour has a price of approximately $3.50 to $5.00 per litre and the powdered stuff (Franco’s) costs about $3.25/L. Basically, with the freshly prepared bar mix, you get better quality at a lower price, but there is a slight amount of labour required to make it from scratch. The benefit is that a better quality drink will pay for itself in a short period, both in tips for the bartender and increased business.
The sour mix recipe is a little more complex than the standard citrus juice / simple syrup mixture, but that’s because it is working on more than just flavour. This recipe also looks at “texture” in the cocktail. This is accomplished by adding some natural sugars (maltodextrin) that increase the viscosity (body) of the sour mix. Also, egg white (optional) is used to give the sour mix the ability to foam. The maltodextrin will provide some foaming capability if you skip the egg white. The zest of the lime gives the sour mix some extra flavour because the oils in the peel are incorporated into the mix. The lime peel also provides some natural green colour for the sour mix. The citric acid helps keep the costs reasonable, and the sour mix consistent. Fruit can be notoriously inconsistent. The corn syrup is to help prevent any re-crystallization of the sugar.
If you want to create separate Lime Sour Mix and Lemon Sour Mix, just follow the same recipe and use only lemon or lime. I rarely use lemon sour, so I will just squeeze fresh lemons with simple syrup to make the lemon sour.
Since you now have a good understanding of what sour mix should be, an understanding of simple syrup is a great next step to making impressive cocktails.