Vegetables, pulses and fruit

Italy is in the northern hemisphere, so the calendar maps onto a British or North American one, with everything running roughly four to six weeks earlier in the south than in the north. What does not map is the length of the windows. Several of the names you will meet on a menu exist for a few weeks a year, and the restaurant that serves them in August is serving something else.

The short windows, in order. Puntarelle (poon-tah-REL-leh), the inner shoots of catalogna chicory, run November to February and are a Roman winter dish, not a summer salad. Roman artichokes, the round spineless carciofo romanesco, run roughly February to May, which is why a spring trip to Rome and a plate of carciofi alla giudia belong together. White asparagus from Bassano is cut by hand over a few weeks between April and mid-June. Broccolo fiolaro from the Vicenza hills is only picked after a hard frost, which converts part of its starch into sugar as antifreeze: before the first frost it is a different, blander vegetable. White truffle runs autumn into early winter.

The tomato explains why the calendar still matters even where supermarkets have abolished it. Sugar arrives in the fruit from the leaves and only while the fruit is attached to the plant. Picked green, a tomato will still turn red and soften, because ethylene handles colour and texture, but its sugar content is frozen at the moment of picking. A vine-ripened summer tomato typically sits around 4.5 to 6 degrees Brix; a winter one picked green stays thinner, sharper and more watery, and no warehouse gives that back.

Cold finishes the job. Below about 12-13 °C, roughly 54 °F, a tomato shuts down production of the volatile compounds that make it smell of tomato, and warming it up again recovers only part of them. This is measurable, not folklore, and it is why a January tomato can look perfect and taste of nothing.

The practical upshot for a traveller or a cook: check what is in season before you plan the meal around a dish. In peak season a vegetable is cheap and everywhere at once, which is the easiest signal to read in any Italian market without speaking a word of the language.

On cured meat a protected name usually guards a process. On a vegetable it has to rest on at least one of three things, and usually two: the variety (often a local landrace never registered as a commercial seed), the soil and climate, or the growing technique. It is worth knowing which one is doing the work, because that tells you what you actually lose by substituting.

San Marzano is the soil case. The Agro Sarnese-Nocerino, inland from Naples, is a plain of volcanic deposits from Vesuvius: deep, loose, potassium-rich ground that holds water without drowning roots, which suits a long thin-skinned tomato with few seeds. Note what the PDO covers: the rulebook requires hand picking in successive passes and certifies the processed product, peeled whole or in fillets, in the can. A genuine can carries the PDO mark plus the consortium's serial numbering, and the certified growing area is small, which is the arithmetic behind how rarely the real thing appears abroad.

Radicchio Rosso di Treviso Tardivo is the technique case, and the most extreme one in the Italian vegetable canon. Heads are lifted after the frosts and forced in the dark with their roots standing in spring water, which surfaces at a near constant 11-13 °C. Over two or three weeks the plant pushes out new leaves without light: white ribs, deep red blades, crunchy and bitter instead of leathery. Then each head is trimmed by hand under running water. What goes into the tank and what comes out are not the same vegetable, which is why it costs several times what a supermarket chicory costs.

Tropea onion is the soil-and-climate case. Coastal Tyrrhenian sand is free-draining and poor, the climate mild: the bulbs build sugar and stay low in the sulphur compounds that make a northern onion sharp and make you cry. Three different products sit under the one PGI, depending on when they are lifted: spring onion, fresh onion and storage onion. Only the last keeps.

One caution before you pay a premium. PDO and PGI guarantee origin and method, not the quality of the particular crate. And two other marks travel alongside them: PAT, a ministry list of traditional products with over five thousand entries, which records that something has been made a certain way for at least twenty-five years and nothing more, and Slow Food Presidia, which are a private association's projects rather than an EU designation.

Farro (FAR-roh) is the word that causes most confusion in English, because it is not one grain. It covers three hulled wheats: einkorn, called farro piccolo; emmer, farro medio, which is what Farro della Garfagnana PGI is and what an Italian recipe almost always means; and spelt, farro grande. English menus translate all three as spelt, which is wrong two times out of three. Buying it, the label that matters is not the species but the processing: pearled (perlato) has lost its outer bran and cooks in about twenty minutes with no soaking, semi-pearled and hulled (decorticato) keep it and want hours of soaking. And to settle the recurring question: all farro contains gluten and none of it is suitable for coeliacs.

The same caution applies to grani antichi, the ancient grains marketing. Senatore Cappelli, the one you see most, is a 1915 selection rather than a medieval survivor, and its reputation comes from a weaker gluten network that industrial bakeries find hard to work with. Weaker is not absent.

With dried pulses, harvest year beats brand. Pulses from the current crop cook in half the time and hold their shape; three-year-old ones never soften properly, whatever you do to them. Small thin-skinned lentils such as Castelluccio di Norcia PGI, grown on plains at 1,300-1,500 m, need no soaking at all and stay whole, which is why they end up in the New Year's Eve lentils-and-cotechino. Larger lentils and all beans do need it. Two technical points that save dinners: acid toughens skins, so tomato, wine and vinegar go in late, while salt in the soaking water softens rather than toughens, contrary to the usual kitchen lore.

Dried beans need a genuine boil. Raw or undercooked, they contain phytohaemagglutinin, a lectin that causes sharp gastrointestinal illness and is destroyed only by at least ten minutes at a full boil. That is the reason dried beans should never go straight into a slow cooker on low without being boiled hard in a pan first.

Cicerchia (chee-CHER-kyah) is the grass pea, Lathyrus sativus, and it deserves an accurate paragraph rather than either silence or alarm. It contains ODAP (beta-ODAP), a non-protein amino acid that is neurotoxic. Neurolathyrism, an irreversible spastic weakness of the legs, is documented where grass pea was a dietary staple for months during famine, with little else to eat. ODAP is water-soluble, and the handling follows from that: soak 12 to 24 hours in plenty of water, change it two or three times, throw every change away, then cook in fresh water which is also discarded. Italian landraces are low in ODAP and here it is an occasional dish, so the practical risk is remote. The procedure is still the procedure, and the soaking water is never used for cooking.

Italian nuts are expensive for reasons that are arithmetic rather than romantic. Nocciola Piemonte PGI is the Tonda Gentile Trilobata hazelnut, the one behind gianduja and Piedmontese cake: in shell it yields roughly 40-45 per cent kernel, and half its value to a pastry kitchen is that the skin slips off cleanly when roasted. Pistacchio Verde di Bronte PDO grows on lava terraces on the flanks of Etna, is picked by hand, and is harvested only in alternate years, the odd-numbered ones, because in the resting year the flower buds are stripped so the tree recovers. Half a crop every two years is the whole explanation for the price of a jar of pistachio cream.

The fault to check for is rancidity, not size. Unsaturated fats oxidise with oxygen, light and heat, and the result reads as cardboard, paint or old oil, on the nose before the palate. The shell is the best packaging ever devised because it is an oxygen barrier: in shell, think months; shelled and loose from an open bin, weeks; ground into flour, days. Keep shelled nuts sealed in the fridge or freezer. Taste one before buying a kilo. What you never taste is anything with dark blotches or visible mould, since that is the picture associated with mycotoxins: discard it rather than trimming it.

Chestnuts split into two commercial classes that English blurs. A marrone gives one to three nuts per burr, mostly without an internal division, with a skin that peels away, which is why it becomes marron glacé; an ordinary castagna gives three smaller, often divided nuts. To test a bag, drop them in water and throw away the floaters, which are either dried out or occupied by a larva. Sicilian dessert almonds, from Pizzuta d'Avola to Romana, are prized for high oil and intense aroma, which is the same richness that makes them go rancid fastest.

Italian citrus makes sense once you understand albedo, the white spongy layer between the coloured skin (the flavedo, where the essential oils sit) and the segments. A cedro, the citron, is nearly all albedo with very little flesh, and the albedo is the part you eat: sliced raw into salad in Calabria, or candied into the peel in panettone. Bergamot sits at the other extreme: it is grown along the Reggio Calabria coast for the essential oil in its skin, the smell of Earl Grey tea, while the flesh is too sour and bitter to be worth eating.

Sorrento lemons, PGI, are the opposite of a juicing lemon: thick skin loaded with essential oil, which is why they carry limoncello and the lemon desserts of the Amalfi coast. If a recipe wants zest, ask for fruit that has not been waxed or treated after harvest, since post-harvest coatings live exactly where you are about to grate. Otherwise buy citrus by weight in the hand: heavy for its size means juice, light means weeks in storage and flesh that has shrunk away from the peel.

A fridge was designed to slow bacteria, not to please plants, and on several of these it does real harm. Tomatoes below about 12-13 °C (54 °F) stop making their aroma compounds and go mealy: keep them on the counter, stem side down, out of the sun, and refrigerate only once cut. Basil blackens below roughly 10 °C and belongs in a glass of water at room temperature, treated like cut flowers. Potatoes below about 4-6 °C convert starch into reducing sugars, which tastes oddly sweet and, when you then fry them hot, feeds the Maillard reaction and raises acrylamide: they want darkness, air and about 6-10 °C. Onions and garlic want dry and ventilated, never a sealed bag, and never next to potatoes, which give off moisture. Citrus takes chilling injury in a cold fridge: pitted skin, flattened aroma, and it dries out anyway.

Then there is ethylene, the ripening hormone, which is the reason a tidy fruit bowl can rot faster than a messy one. Strong emitters: apple, pear, ripe banana, peach, apricot, plum, fig, persimmon, melon, avocado, ripe kiwi and the tomato itself. Sensitive to it: broccoli and cabbage, which yellow; lettuce, which develops russet spotting; carrots, which turn bitter; then cucumber, asparagus, green beans, and potatoes, which sprout. The rule is simply to keep the two groups apart, in separate drawers or separate bags.

The same hormone is a tool when you want it. A rock-hard avocado or an unripe kiwi, shut in a paper bag with a ripe apple, will be ready in a couple of days: paper holds the gas in while letting excess moisture out, which is exactly what plastic fails to do.

The sealed plastic bag is the commonest mistake in a home fridge. Harvested vegetables go on respiring and transpiring: water condenses on the plastic, runs back onto the surface, and a wet surface is where rot starts. Use perforated bags, a cloth, or a bag with a sheet of paper inside to absorb condensation. Mushrooms go in paper, never plastic. Nothing gets washed before storage, only before use.

Finally the truffle, because the myth is widespread and expensive. Do not store a truffle in rice. Rice is hygroscopic: within a day it draws out moisture, and the truffle loses weight and aroma while the rice gains a vague perfume you did not pay for. Keep it in a closed glass jar in the fridge, wrapped in kitchen paper changed daily, and eat a white truffle within three to five days. One consolation about frozen vegetables: industrial freezing happens within hours of harvest, while fresh produce may have a week of travel behind it, and on vitamin C the comparison rarely goes the way people assume.