Mostarda

Mostarda is whole or chopped fruit candied in sugar syrup, then flavoured with a few drops of mustard essential oil. The effect is unlike anything else in European preserving: pure sweetness on the palate, and a sharp volatile heat that rises through the sinuses and disappears almost immediately.

That heat is chemically different from chilli. Capsaicin binds to receptors on the tongue and stays there; allyl isothiocyanate, the compound in mustard oil, evaporates upward and clears within seconds. You can eat a fiercely hot mostarda without wrecking the rest of the meal, because every spoonful resets.

The name has nothing to do with the mustard plant. It comes from mustum ardens, burning must, because medieval cooks preserved fruit in cooked grape must and made it 'burn' with crushed mustard seed. Sugar replaced the must centuries ago, but the word stayed, and it is the root of endless confusion with French moutarde and English mustard.

There is no single mostarda. Four regional families exist, all from the Po valley, differing in fruit, cut, syrup thickness and how violent the mustard is: Cremona, Mantua, Voghera and Vicenza.

The first impression is candied fruit and nothing else: pear, cherry, fig, orange peel, thick syrup, straightforwardly sweet. Then, about two seconds in, the mustard arrives, not on the tongue but behind the nose, like a mouthful of very fresh wasabi or fresh horseradish. Your eyes may water. Then it is gone.

The fruit keeps its own character throughout. A cherry tastes like a cherry, a fig like a fig; the syrup carries them rather than flattening them into jam. Traditional artisan mostarda from Cremona is genuinely fierce. Supermarket versions are usually pitched at a fraction of the strength, and mostarda from Voghera or Vicenza is milder still: closer to a sweet fruit preserve with an edge.

What it is not: sour, vinegary, spiced or savoury. There is no cumin, no ginger, no onion, no vinegar. That is the whole difference from chutney.

The historic use is bollito misto, the Sunday cart of boiled meats in Lombardy, Emilia and Piedmont: beef, capon, tongue, cotechino. Mostarda arrives alongside salsa verde and grated horseradish, and its job is to cut through fat and wake up meat that is by nature soft and mild. One small spoonful per mouthful of meat.

The second use is the cheese board, where it belongs with cheeses that can fight back: Gorgonzola, mature Taleggio, long-aged Parmigiano, hard sheep's cheeses. On fresh or mild cheese it simply overwhelms.

The third is Mantuan and it is an ingredient rather than a condiment. Tortelli di zucca are filled with roast pumpkin, crushed amaretti, grated Grana Padano, nutmeg and finely chopped mostarda. Leave the mostarda out and the filling is just sweet; put it in and the whole dish acquires a spine.

Beyond tradition it is excellent with roast pork, duck, and any cured pork sausage. Always serve it cold or at room temperature, because heating it drives off the mustard entirely.

Sugar and mustard essence between them make mostarda one of the longest keeping things in an Italian larder. A sealed jar sits in a dark cupboard until the best before date printed on it, commonly two to three years out, and needs nothing else. Once opened it moves to the fridge, closed tight, and Italian producers generally give three to six months from there. Always take it out with a clean dry spoon: fruit dragged out of the syrup starts drying at the top of the jar.

What fades first is the mustard. Allyl isothiocyanate is volatile, so every time the jar is opened some of the sharpness leaves with the vapour, and a jar six months into its life is noticeably sweeter and rounder than a fresh one. The fruit meanwhile keeps absorbing syrup, darkens slowly, and softens. Sugar crystals forming on the rim or in the syrup are the syrup coming out of solution, and warming the jar gently in a bowl of hot water redissolves them. Do not freeze it; the fruit cells rupture and the pieces come out slack.

Mostarda is not mustard, despite what the word does to English speakers, and it is not chutney either. In the jar you should see whole or large pieces of fruit suspended in a clear, thick, almost glassy syrup, the fruit translucent and holding its shape rather than collapsed into a puree. Colours stay close to the fruit: green figs, amber pears, red cherries, pale quince. The heat is not chilli. Open the jar and the vapour catches the back of the nose the way horseradish does, then fades.

The ingredient list should be short and must name mustard: senape, mustard essence or essential oil of mustard, alongside fruit and sugar. Without it the jar is candied fruit. Regional styles differ legitimately and the label usually says which: Cremona keeps the fruits whole in clear syrup, Mantova is chunky apple or quince, Vicenza is a thick paste, and Piedmontese cognà contains no mustard at all, being cooked grape must with fruit. Expect $12 to $22 for a 380 gram jar abroad, and treat anything in the chutney price bracket as a different product.

In the US, Eataly, Gustiamo, Formaggio Kitchen and most serious cheese counters stock Cremona-style mostarda; expect 14 to 26 dollars for a 380 g jar, roughly 17 to 31 dollars per pound. In the UK, Italian delis, Ocado and specialists such as Vorrei carry it at 8 to 16 pounds a jar, or 20 to 40 pounds per kilo.

Read the ingredients: they should say fruit, sugar and mustard essential oil, and very little else. Glucose-fructose syrup at the top of the list, added pectin or generic 'flavourings' all point to a cheap industrial version.

Look at the fruit through the glass. It should be recognisable, a cherry that looks like a cherry and a pear shaped like a pear, and should carry its own colour rather than a uniform orange. The syrup should be clear and pourable, not set like jelly.

If you are buying for tortelli di zucca, look specifically for Mantuan-style apple mostarda, sold as mostarda di mele campanine. It is harder to find abroad and usually needs ordering online.

Cremona is the obvious pilgrimage: the old shops in the centre sell mostarda loose from the jar and will let you taste before buying, and the town's November nougat festival draws the mostarda makers into the square as well.

Mantua, an hour east, is where you eat tortelli di zucca, served all year but ritual on Christmas Eve, in trattorie in the centre and in the villages along the Mincio.

Voghera and the Oltrepò Pavese hills serve the sweeter, gentler style, usually with local goat's cheese.

Anywhere in the Po valley between November and February, follow the bollito cart. That is the season when mostarda makes sense and when trattorie put it on the table without being asked.