San Marzano Tomatoes

San Marzano is a processing tomato: elongated, six to eight centimetres long, with a thin skin that slips off without a peeler, dense flesh, very few seeds and low water content. Its full protected name is Pomodoro S. Marzano dell'Agro Sarnese-Nocerino DOP, registered by the EU in 1996.

It is not a salad tomato and was never meant to be eaten raw. The DOP rules govern the canning as tightly as the growing, and in practice you buy it as whole peeled tomatoes or fillets packed in their own juice, with a basil leaf and salt and nothing else: no concentrate, no colouring.

Growing area: about forty municipalities across the provinces of Salerno, Naples and Avellino, on volcanic soil between Vesuvius and the Lattari mountains. Harvest runs 30 July to 30 September and is done entirely by hand, in repeated passes along the same row.

Sweet first, then a low, clean acidity, then a faintly bitter finish that keeps it from tasting like sauce out of a jar. There is very little of the sharp metallic edge that cheap canned tomatoes carry, because the fruit goes in ripe and the flesh is dense rather than watery.

Cooked briefly, it stays bright and fruity, and twenty minutes with garlic and oil is enough, and the sauce comes out sweet without any sugar added. If you find yourself reaching for the sugar jar, the tomato was not what the label said.

Raw from the can, straight onto pizza dough as the Neapolitans do it, the flavour is fresher and lighter than any cooked sauce, with the salt and the basil doing all the seasoning.

For sauce, keep it short. Garlic in good olive oil, the tomatoes crushed by hand and never blended, since blending whips in air and dulls the flavour, salt, twenty minutes, basil off the heat. San Marzano is low in acid, so it does not need long cooking to soften, and past forty minutes it loses the fresh note it was bought for.

For Neapolitan pizza, do not cook them at all. Crush by hand, add a little salt, spread a ladleful on the dough and let ninety seconds in a very hot oven do the rest. The Associazione Verace Pizza Napoletana specifies San Marzano dell'Agro Sarnese-Nocerino DOP or equivalent long peeled tomatoes for exactly this.

Where the pieces should stay whole (acqua pazza, braised octopus, parmigiana, long meat ragù) the firm flesh is an advantage.

Never throw away the juice in the can. It is thick and sweet and belongs in the pan.

Unopened tins live in a dry cupboard until the date printed on them, usually two to three years out, and away from the cooker: warmth slowly dulls the colour and flattens the aroma even inside a sealed tin. Stack them where you can see the seams. A tin dented across a seam, or one with a lid that has risen, is a question for the shop that sold it rather than something to shelve. Put new purchases at the back so the older tins move first.

Once opened, do not keep tomatoes in the tin. Acid flesh against bare metal takes on a metallic edge within hours, so tip everything into glass or ceramic, cover it, and keep it in the fridge for three to four days; the flesh softens a little each day and the juice separates from the pulp. Surplus freezes for around six months, fruit and juice together in flat bags or ice cube trays. Thawed, the tomatoes collapse, which suits sauce and rules out any dish that needs a whole piece. Cooked sauce holds about five days chilled.

Three things have to appear together on the tin: the full wording Pomodoro S. Marzano dell'Agro Sarnese-Nocerino DOP, the red and yellow European DOP roundel, and the numbered Consorzio seal with the name of the certifying body. If one of the three is missing, it is not the DOP tomato, whatever the front of the label suggests. The phrases to read slowly are San Marzano style, San Marzano variety, San Marzano type and packed in Italy. All of them are legal, and none of them means the fruit was grown to the DOP rules.

Open the tin and the fruit is whole and long, six to eight centimetres, tapering to a slight point, with two seed chambers rather than three or four. The colour is a full even red rather than orange, and the liquid is thick juice rather than pink water. Raw, the flesh is meaty and low in sharp acidity with almost no seeds; a metallic or bitter finish points to fruit picked green. Price sorts the rest: DOP tins run roughly $5 to $9 or £3.50 to £6 for 400 g, against a dollar or two for ordinary plum tomatoes.

In the US, expect 5 to 9 dollars for a 28 oz can of genuine DOP. Eataly, Gustiamo, Whole Foods and well-stocked Italian grocers carry it; supermarket shelves are full of cans that use the name without the certification, so read before you reach. A can at 2 to 4 dollars is telling you what it is.

In the UK, 3 to 5 pounds for a 400 g tin at Waitrose, Ocado, Natoora or an Italian delicatessen. Italian grocers in London and Manchester often have the 2.5 kg catering tins for around 12 to 18 pounds, which is far better value if you cook a lot.

In Italy, 2.50 to 4.50 euros for a 400 g tin and 9 to 14 for the catering size.

The check is always the same: the full wording 'Pomodoro S. Marzano dell'Agro Sarnese-Nocerino DOP', the red and yellow EU DOP logo, and the numbered Consorzio di Tutela seal naming the certifying body. Three marks, all present, or it is a different tomato.

Naples, in a pizzeria that names the DOP tomato on its menu, and there are fewer than the marketing suggests. Asking to see the tin is not rude; several of the best places will show you without being asked.

In the growing area itself, between late July and September, the harvest runs in plain sight along the roads around San Marzano sul Sarno, Sarno, Striano and Angri, and the late-summer village festivals put the tomato at the centre of the plate rather than under it. Angri and Nocera Inferiore are where the Italian canning industry was born at the end of the nineteenth century.

Combine it with the coast: Cetara, on the Amalfi side of the same mountains, supplies the anchovies that share half the local recipes with this tomato.