Mazagran is cold coffee with lemon, and its origin is a nineteenth-century French garrison at Mazagran in Algeria, where soldiers reportedly drank coffee cut with water and lemon in the heat.
Returning soldiers brought it to France, and it took hold most firmly in Portugal, where it remains a summer standard.
Why lemon and coffee work
Coffee is acidic already, and its acids are largely citric and malic — the same family as lemon. Adding lemon amplifies rather than clashes, and the result reads as bright and refreshing rather than odd.
It works best with a bright, fruity, light-roast coffee and poorly with a dark chocolatey one.
The Portuguese version
Espresso, sugar, lemon juice or a slice, ice, in a tall glass. Sometimes topped with sparkling water, sometimes with a splash of rum.
The Austrian version
Confusingly, Austria has a different Mazagran: cold coffee with sugar and rum, no lemon, served over ice.
Making one
A double espresso, sweetened while hot, cooled. Pour over ice with the juice of a quarter lemon and a slice. Top with sparkling water if you want it longer.
The modern relative
Espresso tonic is the same instinct — bitterness and citrus over ice — arrived at independently by Scandinavian cafés a century later.