Limoncello

Limoncello is an infusion of lemon zest in neutral alcohol, sweetened with sugar syrup. Four ingredients: lemons, alcohol, sugar, water. Everything else on a label is either a shortcut or a fault.

The rule no serious producer breaks is that the juice never goes in. Lemon aroma lives in the essential oils held in the flavedo, the thin yellow outer layer of the peel. Juice contributes only water and citric acid: it clouds the liqueur permanently, makes it unstable and turns it grey within weeks. A limoncello made with juice tastes sour rather than aromatic: that is the giveaway.

The second rule concerns the pith, the white albedo under the zest. It is bitter and must stay on the fruit. Peel with a thin-bladed vegetable peeler rather than a knife, and if white comes away with the yellow, the liqueur will turn bitter after a few months in the bottle.

Finished strength runs 25-32% ABV. The cloudiness that appears when it chills or when you add water is not a defect but proof that real essential oils are present: they are insoluble in water and drop out as microscopic droplets once the alcohol concentration falls. A limoncello that stays crystal clear at freezer temperature is almost always flavoured rather than infused.

Lemon oil rather than lemon juice, which sounds like a technicality until you taste it. The aroma is the smell of a lemon being zested, bright and slightly resinous, with no acidity behind it. The sweetness arrives second and the alcohol third, warming rather than burning if the liqueur has rested properly.

Served at freezer temperature it is thick, almost syrupy, and coats the glass. The cold suppresses the sugar, which is why the same liqueur tastes cloying at room temperature and clean at -18°C.

A good one finishes clean and slightly bitter in the way citrus peel is bitter. A lingering harsh bitterness means pith went in with the zest. A candied, sweet-shop character with no aroma behind it means flavouring rather than infusion.

Keep the bottle in the freezer and the glasses with it. At 25-32% ABV it will not freeze; it turns thick and syrupy and pours slowly, which is exactly right. Thirty to forty millilitres is a serving. At room temperature the same liqueur reads as sugary and hot, so this is not a stylistic preference.

The moment is after the meal, after coffee, and the role is digestive rather than dessert.

In the kitchen it earns its place. It soaks the sponge in a delizia al limone, the domed lemon-cream cake of the Amalfi Coast; it replaces rum in the syrup for a babà; it goes over strawberries or peaches instead of sugar. A spoonful over fiordilatte gelato is the simplest good use of an open bottle.

For a cocktail, the sgroppino is the one that works: lemon sorbetto, prosecco and a measure of limoncello blended together and served immediately in a chilled glass.

Do not mix it with chocolate, and do not use it in tiramisù. Citrus oil and cocoa fight each other.

Sealed and kept cold and dark, a bottle holds its aroma and colour for a year or two. The freezer is both the right storage place and the right serving temperature: at around 30 per cent alcohol it never sets solid, it just goes thick and syrupy. Light does more damage than heat. A clear bottle left on a shelf near a window drifts from pale yellow towards ochre within a few months and loses its top notes, so anything not in dark glass belongs in a cupboard.

Once opened, the change is one of aroma rather than anything else. The peel oils are volatile and the air space above the liquid grows every time you pour, so the citrus edge softens: the first six months are the best of it, and after a year the drink is rounder and quieter. Decanting into a smaller bottle slows that down. Crema di limoncello is a separate case, since it contains milk or cream: it lives in the refrigerator, carries a date of its own, and separates into layers that a shake puts back together. Follow its label and the producer.

Count the ingredients on the back label. Lemons, alcohol, sugar, water: four. Natural lemon flavouring in the list means part of the aroma did not come off a peel, and a colour listed as E102, E104, Yellow 5 or Yellow 10 means the shade was added. Real limoncello is a pale, soft, faintly cloudy yellow that shifts from batch to batch because the fruit does; an identical fluorescent yellow bottle after bottle is dye. Serious producers name the fruit, usually Limone di Sorrento IGP or Limone Costa d'Amalfi IGP, while a label that says only Italian lemons has said all it can.

Two checks settle it. Put the bottle in the freezer: essential oils come out of solution, so the liquid thickens and goes opaque. Add a splash of water to a glass and it turns milky. A limoncello that stays glassy and thin through both is carrying very little peel oil. Strength usually sits between 25 and 32 per cent. In the US and UK, bottles under about 15 dollars or 12 pounds are the flavouring route; the Sorrento and Amalfi bottlings run roughly twice that.

Look for two things on the label: a four-ingredient list, and a named lemon origin (Limone di Sorrento IGP or Limone Costa d'Amalfi IGP). Producers using protected lemons always say so, because it is the expensive part. A bottle that only says Italian lemons is telling you the most it can.

In the US, Italian importers and better liquor stores carry Campanian limoncello at 22 to 38 dollars for a 750 ml bottle; Eataly and specialist online sellers stock several producers. In the UK, expect 18 to 30 pounds a bottle from Italian delicatessens and the larger supermarkets' Italian ranges. Anything under 15 dollars or 15 pounds is generally a flavoured liqueur made outside Campania.

In Italy itself, 50 cl of artisan limoncello runs 12 to 20 euro and 70 cl runs 18 to 28. Industrial bottles sit at 7 to 12 euro a litre.

Ignore the painted ceramic bottles sold along the coast road. You are paying for the container.

Start on the Sorrento peninsula (Sorrento itself, Massa Lubrense, Sant'Agata sui Due Golfi) where you can still see the groves under their pagliarelle, straw mats stretched over chestnut-pole frames. A number of farms open to visitors and walk you through the grove before the tasting.

On the Amalfi Coast the landscape turns vertical. The terraces above Amalfi, Minori, Maiori and Ravello are hand-built dry-stone walls on slopes no machine can work. The best way to see them is the Sentiero dei Limoni, the stepped path linking Maiori to Minori straight through the groves.

Capri, and Anacapri in particular, has a long tradition of family production and lemon gardens that are part of the island's landscape. Procida and Ischia make less-known versions, often more genuinely artisan than what is sold on the mainland tourist strip.

Go between February and May, when the harvest is at its height and the groves smell of blossom. August on that coast is about crowds, not lemons.