Gomme syrup is a sweetener used in mixed drinks and coffee. Unlike simple syrup, which is made with sugar and water, gomme syrup includes gum arabic, which the French call gomme, as an emulsifier to thicken the syrup and create a smoother tasting cocktail. Gum arabic prevents sugar from crystallizing in solution, allowing for sweeter syrup.
The thicker, sweeter syrup helps to smooth the harsh flavor of alcohol in cocktails. While rarely available in bars today, many original recipes for classic cocktails, dating to before Prohibition, call for the thicker syrup. Gomme syrup is available in several commercially prepared products, available at better restaurant or bar supply stores as well as online.
However, it is also possible to prepare gomme syrup at home. The most difficult part of the process is locating food or medical grade gum arabic. However, it is available at some local baking supply stores, health food stores and online. Syrup recipes vary as to whether one should dissolve the gum arabic in an equal amount of water by boiling before adding sugar or add the powder to boiling simple syrup. If gomme syrup is not available, bartenders often substitute simple syrup, but they sacrifice the quality of the drink with this substitution.