Elderflower liqueur arrived in 2007 as St-Germain and was nicknamed "bartender's ketchup" within a year, because a half ounce makes almost anything taste better: floral, honeyed and faintly tropical, it softens gin into an Elderflower Collins, lifts prosecco into a Hugo, and turns a Gimlet into an Elderflower Gimlet that converts people who thought they did not like gin.

What is elderflower liqueur?

A sweet liqueur made from the blossoms of the elder tree, picked for a few weeks in late spring, macerated and blended with sugar and a neutral spirit, usually at around 20 per cent alcohol. Elderflower cordial (non-alcoholic) is an old English and Alpine tradition; the liqueur is modern. Robert Cooper launched St-Germain in 2007 in a bottle styled like an Art Deco lamp, and it became the fastest-adopted new ingredient in decades. The Hugo, from the South Tyrol in 2005, used elderflower syrup; bars switched it to the liqueur. Giffard, Drillaud and several craft distillers now make their own.

What it tastes like

Honeysuckle, pear, lychee and a little grapefruit, sweet but with a clean, floral finish rather than a syrupy one. It pairs with gin above all, with vodka, with tequila in the Jalisco Flower, with mezcal in the Maximilian Affair, with Irish whiskey in the Irish Maid, with cucumber in the Gin Garden, and with anything sparkling. Its weakness is sweetness: it needs lime or lemon beside it, or it reads as perfume.

How to use it

A half to three-quarters of an ounce in a shaken sour or a Collins, where it replaces most of the syrup; an ounce in a spritz with prosecco and soda; a quarter ounce as a modifier in a Martini. It is sweet enough that a drink with elderflower rarely needs simple syrup too. Chill it; it is better cold. A home elderflower cordial (blossoms, sugar, lemon, citric acid) plus a little vodka is a fair homemade version in June.

Substitutes

Elderflower cordial or syrup at two-thirds the measure plus a splash more spirit, which is what the original Hugo used. Lillet Blanc for a floral, less sweet note. Pear liqueur or lychee liqueur for a similar fruit. Honey syrup in a pinch, which gives the sweetness without the flower.

What to buy

St-Germain is the standard and still the best balanced. Giffard Fleur de Sureau Sauvage is drier and cheaper and many bartenders prefer it. Drillaud and Thatcher's are decent budget bottles. Bottle size matters: it fades once open, so buy the 375 ml unless you make a lot of Hugos.

Storage and shelf life

Six months in the fridge once opened, after which the floral top notes dull and it tastes merely sweet; St-Germain's own advice is to use it within six months. Sealed, two or three years in a cool, dark place. Keep it cold.

Cocktails with elderflower liqueur

The spritz: the Hugo Spritz. The gin drinks: the Elderflower Collins, the Elderflower Gimlet and the Gin Garden. The whiskey one: the Irish Maid. The agave ones: the Jalisco Flower and the Maximilian Affair. Every drink that uses elderflower liqueur is listed below.

Questions

Is St-Germain the only one? No; Giffard, Drillaud and others make good elderflower liqueurs. St-Germain is the best known.

How strong is it? About 20 per cent, half the strength of gin.

Why does my elderflower drink taste like perfume? Not enough acid. Add lime or lemon, and cut the measure to a half ounce.

What is a Hugo? Elderflower liqueur, prosecco, soda, mint and lime over ice: the South Tyrolean spritz.

Does it go with whiskey? Irish whiskey, yes, with lemon and cucumber in the Irish Maid; bourbon less so.