2 to 1 'rich' sugar syrup versus 1 to 1 'simple' syrup

The balance between sweet and sour is crucial to the majority of cocktails and consistently producing balanced cocktails is made easier when using sugar syrup with a known and constant sweetness.

Sugar syrups tend to be made according to two recipes:

One part sugar to one part water (1:1)

1:1 syrup can be made by shaking sugar and room-temperature water together in a sealed container, so it is appropriately known as 'simple syrup'.

1:1 is the most common type of syrup used in American bars (but even in America, there is a growing trend towards the use of 2:1 syrup). The appeal of 1:1 syrup is that no heat is needed to dissolve the sugar in the water and 1oz (30ml) of "simple syrup" roughly balances the acidity of 1oz (30ml) citrus juice so making balanced cocktail recipes easy.

Two parts sugar to one part water (2:1)

Known as "rich sugar syrup," 2:1 is the most common sugar syrup found outside America and is the style used in Difford's Guide recipes.

When measured by volume rather than mass [see below], 2:1 sugar syrup is also around the same degree of sweetness found in most commercially produced bottled sugar syrups. European bars commonly buy syrup rather than make their own to help ensure consistency, and syrups are widely stocked in supermarkets. The willingness to buy rather than make syrups is also driven by the fact that making 2:1 syrup involves the faff of gently heating and stirring the water and sugar to ensure all the sugar dissolves.

20ml (2/3oz) of "rich syrup" roughly balances the acidity of 30ml (1oz) citrus juice.

2:1 'rich' syrup versus 1:1 'simple' syrup

2:1 syrup is superior to 1:1 syrup as the use of 1:1 sugar syrup adds additional, perhaps unwanted, dilution to a drink compared to 2:1 syrup, typically around 5 to 8%, depending on the recipe. It's a small percentage but worth eliminating. If desirable in a particular cocktail, dilution can be controllably increased by adding a measured amount of chilled water. If you worry about over-dilution from "wet" melting ice, then you should also consider the amount of water in your sugar syrup.

Converting cocktail recipes using 2:1 rich syrup to equivalent 1:1 simple syrup

Confusingly, if a cocktail recipe specifies 10ml of 2:1 rich sugar syrup, the equivalent is NOT 20ml of 1:1 as would seem logical but nearer to 15ml of 1:1 (actually 13.56ml) simple syrup. 2:1 sugar syrup is 1.35 times sweeter than 1:1 syrup (not twice as sweet).

A liquid's sweetness is measured on a scale called 'brix'.
2:1 rich sugar syrup (by volume) = 65.1°brix
1:1 simple sugar syrup (by volume) = 48.0°brix
The difference in brix between the two concentrations of sugar syrup illustrates that 1:1 simple syrup is 26.27% less sweet than 2:1 rich syrup. And conversely, 2:1 is a little more than a third sweeter (35.62%) than 1:1 simple syrup.

Equivalent sweetness rounding to nearest bar measure
5ml (1 barspoon) 2:1 syrup = 7.5ml (¼oz) 1:1 syrup
7.5ml (1/4oz) 2:1 syrup = 10ml (1/3oz 1:1 syrup
10ml (1/3oz) 2:1 syrup = 15ml (½oz) 1:1 syrup
15ml (½oz) 2:1 syrup = 20ml (2/3oz) 1:1 syrup
20ml (2/3oz) 2:1 syrup = 30ml (1oz) 1:1 syrup

Measuring by volume rather than mass

When making sugar syrup, some people measure by weight (e.g. 2kg of sugar to 1kg of water), while others measure by volume (e.g. 2 cups of sugar to 1 cup of water). Whether following a 1:1 or 2:1 ratio, measuring by weight results in a sweeter syrup than that made by measuring by volume.

For ease and to produce a 65°brix syrup, I measure by volume – 2 cups of sugar to 1 cup of water.