How to Make Irish Coffee: The Original Recipe and How to Float the Cream

An Irish coffee is hot, strong coffee with Irish whiskey and sugar stirred in, topped with a layer of lightly whipped cream that you drink the coffee through. The International Bartenders Association's version is 50 ml Irish whiskey, 120 ml hot coffee, at least a teaspoon of sugar and 50 ml of chilled fresh cream. The hard part is the cream, and the trick is simple once you know why it floats.

The recipe

1. Brew strong coffee and keep it hot.
2. Whip the cream lightly — just until it thickens and leaves a soft trail, but still pours.
3. Preheat a stemmed glass with boiling water for a few seconds, then empty it.
4. Add the sugar and whiskey, then the hot coffee to about a centimetre below the brim. Stir until the sugar has completely dissolved.
5. Float the cream. Hold a spoon upside down just above the surface and pour the cream slowly over its back, raising the spoon a little as the layer builds.
6. Do not stir. Drink the hot coffee through the cool cream.

The Foynes Flying Boat & Maritime Museum, which tells the drink's origin story, gives the same method: brown sugar and Irish whiskey in a warmed glass, strong black coffee to within a centimetre of the rim, lightly whipped cream poured over the back of a spoon — and no stirring afterwards.

How to float the cream

Irish coffee is a small exercise in density. A layer floats on a liquid when it is lighter, volume for volume, than the liquid underneath. Three things tip the balance the cream's way.

• Fat floats. Cream is mostly water and milk fat, and fat is less dense than water — the reason cream rises to the top of unhomogenised milk.
• Air lightens it further. Whipping the cream lightly folds in tiny air bubbles, lowering its density and thickening it so it does not run straight into the coffee. Too little whipping and it mixes in; too much and it sits in lumps rather than a smooth collar.
• Sugar makes the coffee heavier. Dissolved sugar raises the density of the coffee below, widening the gap between the two layers. That is why the classic recipes insist on sugar, and why it must be fully dissolved before the cream goes on.

The spoon does the rest. Pouring over the back of a spoon held just above the surface spreads the cream gently, so it does not plunge through.

The Buena Vista Cafe in San Francisco learned all this the hard way. When it first tried to recreate the drink in 1952, the cream kept sinking. According to the bar, the answer came from the city's mayor, a dairy owner: cream aged for 48 hours and frothed to a precise consistency would float "as delicately as a swan".

Where Irish coffee came from

Coffee laced with spirits is far older than Irish coffee — nineteenth-century French writers from Balzac to Flaubert mention the gloria, a mixture of coffee and spirits. But Irish coffee as we know it has a specific birthplace.

In 1943, Brendan O'Regan opened a restaurant in the terminal building at Foynes, in County Limerick, then the transatlantic base for flying boats. His chef was Joe Sheridan, from Castlederg in County Tyrone. According to the Foynes museum, late one winter night that year a flight to New York turned back after hours in bad weather. Staff were called in, and Sheridan was asked to make something warm for the cold, tired passengers. He added Irish whiskey to their coffee. When one passenger asked whether it was Brazilian coffee, Sheridan answered that it was Irish coffee. A few weeks later he presented a refined version in a stemmed glass. (Some accounts date the first one to 1942.)

The drink crossed the Atlantic with a journalist. Stanton Delaplane, a travel writer for the San Francisco Chronicle, had tasted it at Shannon Airport, near Foynes. On 10 November 1952, Jack Koeppler, owner of the Buena Vista Cafe, challenged him to help recreate it, and after much trial and error — including a trip by Koeppler to Shannon — the Buena Vista made Irish coffee its signature. Joe Sheridan himself later emigrated to work there.

What is in the glass

Alcohol. Irish whiskey must legally be at least 40% alcohol. At that strength, 50 ml contains 50 × 0.40 = 20 ml of pure alcohol, or about 15.8 g. The US defines a standard drink as 14 g, so one Irish coffee is about 1.1 standard drinks; at 10 ml to a UK unit, it is 2 units.

Caffeine. The USDA puts brewed coffee at about 40 mg of caffeine per 100 g, so 120 ml of filter coffee carries roughly 48 mg — about half a mug. Strong coffee or a bigger glass will mean more. The caffeine guide has figures for other drinks.

The combination. The CDC notes that caffeine does not reduce the effects of alcohol and can make you feel less affected than you are. A warming Irish coffee late in the evening is also a dose of caffeine close to bedtime — the coffee and sleep guide explains why that matters, and decaf coffee makes an Irish coffee that will not keep you up.

Getting it right

• Use good, strong coffee. The Foynes recipe asks for strong black coffee; filter coffee or an americano both work. Weak or stewed coffee is exposed by the whiskey and sugar. The drip coffee guide covers brewing a good pot.
• Heat the glass. A warm glass keeps the drink hot to the last sip.
• Use fresh, chilled cream. Cold cream whips more easily and contrasts with the hot coffee. Aerosol cream is sweeter and much airier, and sits on top as foam rather than as a smooth layer.
• Dissolve the sugar completely before the cream goes on, or the cream has nothing to float on.

Relatives of Irish coffee

The same formula — hot coffee, a spirit, sugar and floated cream — has spawned a family of drinks: Gaelic or Highland coffee with Scotch whisky, Jamaican coffee with rum, Russian coffee with vodka and Mexican coffee with tequila. Irish cream coffee uses an Irish cream liqueur in place of the whiskey, sugar and cream. For a cold, shaken coffee cocktail, see the espresso martini, and for every café drink in between, the types of coffee drinks guide.