Chestnuts

Chestnuts grow inside a spiny burr that splits open when ripe. How many nuts are in each burr is the whole basis of the Italian classification.

A castagna comes from traditional or wild trees: two or three nuts to a burr, so they press against each other as they grow and end up smaller, with at least one flat face. The inner skin, the pellicle, works its way into the flesh and divides it into lobes, which makes them almost impossible to peel whole.

A marrone comes from selected cultivars: one nut per burr, larger, heart-shaped, with a glossy shell marked by dark stripes and a pellicle that lifts away cleanly. That is why marroni cost roughly double and why only marroni are used for marron glacé.

On top of the botany sits a map of protected names: Marrone del Mugello IGP and Marrone di Caprese Michelangelo DOP in Tuscany, Farina di Neccio della Garfagnana DOP for the flour, Castagna del Monte Amiata IGP; Castagna di Montella IGP and Marrone di Roccadaspide IGP in Campania; Marrone di Castel del Rio IGP in Emilia and Marrone di San Zeno DOP by Lake Garda.

None of this has anything to do with water chestnuts, which are an aquatic sedge tuber from Asia, or with horse chestnuts, which are a different family and are toxic.

Roasted, a chestnut is sweet, starchy and faintly smoky, with a texture between a boiled potato and a dense sponge cake. It is the least oily nut you will meet: most nuts are 50 to 70 per cent fat, a chestnut is around 2 per cent and roughly half water, which is why it behaves like a vegetable in the kitchen and why it goes stale rather than rancid.

Boiled, the flavour is milder and cleaner, closer to a sweet chestnut-flavoured potato, and the texture is softer and wetter. Dried and rehydrated, it concentrates into something almost caramelised.

Chestnut flour is the surprise: pale hazel, very finely milled, and genuinely sweet on its own, with a smoky note from the wood fire used to dry the nuts. Baked into castagnaccio with olive oil, rosemary and pine nuts, it tastes savoury, earthy and not much like a dessert, which is exactly what it was designed to be.

To roast: score each nut with a firm cut across the domed face, through shell and pellicle, over about a third of the circumference. Too shallow and they explode; too deep and they dry out. Use a perforated chestnut pan over a live flame or a very hot oven, 25 to 30 minutes, shaking often.

The peeling trick is steam, not a knife. The moment they come off the heat, wrap them in a damp cloth for ten minutes. The pellicle then lifts away. Let them cool uncovered and it welds itself to the flesh.

To boil: start in cold water with a bay leaf and a few fennel seeds, forty minutes from the boil, and peel while hot.

For castagnaccio, the oldest Tuscan chestnut cake: chestnut flour, water, olive oil, pine nuts, raisins and rosemary, baked forty minutes until the top cracks. No sugar, no eggs, no leavening, and it is not sweet, which surprises everyone the first time.

Savoury uses are underrated: chestnuts in bean soups, crumbled over risotto, roasted alongside pork or game, or puréed into a soup with leek and a little cream.

A raw chestnut is a living seed full of water, and it keeps breathing after picking. Loose and untreated it holds about a week in the refrigerator in a paper bag or a net, never a sealed plastic one, where the trapped moisture works against it. The traditional way to extend that is curing in water: seven to nine days fully submerged with the water changed daily, then two days spread on a cloth until bone dry on the outside. Cured and kept in a ventilated box in the fridge, they run a month or more.

Left as they are, chestnuts lose water steadily. The kernel shrinks away from the shell until it rattles, the shell loses its gloss, and the flesh turns dry and woody rather than milky. Freezing stops it: score them raw, bag them, and they hold a year, roasting straight from frozen with five minutes added. Dried chestnuts keep a year in sealed jars in the dark and need twelve hours of soaking. Chestnut flour is the fragile one, since its fat oxidises: refrigerate or freeze it and go by the milling date.

Weigh one in your hand: it should feel heavy for its size and stay firm when you squeeze it, because a nut that gives has dried and pulled from the shell. The shell wants to be glossy, taut and warm brown, with no pinholes; a hole a millimetre across is where a larva left. The pale scar at the base should look dry and light rather than damp or darkened. Shake it by your ear: if the kernel rattles, it has shrunk inside. Marrone and castagna are different grades: the marrone is larger, heart-shaped, boldly striped and domed on at least one face, while the castagna is smaller with a flatter side and flesh often split into lobes by the inner skin.

The cooking test settles it, since a marrone sheds its inner skin in one piece. Horse chestnuts, the conkers of British parks, are round, smooth and single in a case with few spikes, from a different tree. Chestnut flour should be pale hazelnut with a sweet smoky smell; grey flour with a sharp edge has been milled a while. Fresh chestnuts run 4 to 8 dollars a pound.

In the US, fresh Italian chestnuts appear from October to December in Italian groceries and better supermarkets at 4 to 8 dollars a pound; most of what is sold as 'chestnuts' the rest of the year is vacuum-packed and cooked. Domestic American chestnuts are almost all hybrids, since the native species was wiped out by blight in the early twentieth century, so imported Italian marroni are worth seeking out for roasting.

In the UK, fresh chestnuts are a December supermarket item at 6 to 10 pounds a kilo; Italian delis carry marroni and chestnut flour, and online importers stock Farina di Neccio della Garfagnana DOP.

Chestnut flour costs 12 to 20 euros a kilo in Italy and considerably more abroad. Buy it from a supplier who dates the milling, keep it in the freezer, and use it within six to eight months.

How to pick a good one: heavy for its size, firm under thumb pressure, glossy shell with no pinholes. A one-millimetre hole is a larva's exit. Shake it: if the kernel rattles, it has dried out.

Marradi, in the Mugello north of Florence, holds Tuscany's best-known chestnut festival for the Marrone del Mugello IGP, running every Sunday through October. A heritage steam train runs up from Florence for it, which is the correct way to arrive.

Montella, in the Irpinia hills inland from Salerno, celebrates its own IGP chestnut in late October and early November, and is the place to try the castagna del prete, smoked in a stone drying house, roasted, then rehydrated in water and wine. It barely exists outside Campania.

The Garfagnana in northern Tuscany is where the flour tradition survives: working water mills, stone metati still smoking in autumn, and necci, thin chestnut-flour pancakes cooked between hot iron plates and filled with ricotta, sold at village festivals through October and November.

Outside the two regions, Soriano nel Cimino north of Rome runs an October chestnut festival wrapped around a medieval pageant. And for marron glacé, the tradition is Piedmontese: Cuneo and Turin have been candying them since the late nineteenth century.