There comes a point in late summer when the tomato plants are groaning with fruit, and even the most enthusiastic salad eater can't keep up. You've made chutney, given bags away, and still the glut grows. This is the moment for passata: a smooth, sieved tomato sauce that earns its place in the pantry. The secret to a really good one is slow-roasting the tomatoes first, which deepens their flavour before you ever reach for the sieve.

Why Roast Before Sieving?

Raw tomatoes are watery and their flavour can be thin. Roasting drives off excess water and concentrates sugars, deepening the taste into something rich and sweet. It also loosens skins, making sieving easier. The result is a passata with a robust, almost caramelised character that holds up beautifully in pasta sauces, soups and casseroles.

Preparing Your Glut

Any ripe tomato works, but meaty varieties like Roma, San Marzano or plum types give the best yield. Mixed varieties are fine, though cherry tomatoes need more roasting time. Wash them, remove any tough cores or bruised spots. Halve them through the equator. No need to peel or seed — the sieve will deal with that. If you have a huge glut, work in batches.

The Slow-Roast Method

Heat your oven to 120°C fan (140°C conventional). Arrange halved tomatoes cut-side up on baking trays lined with parchment. Don't crowd them — a single layer is best. Drizzle generously with olive oil, sprinkle with sea salt, and tuck in a few peeled garlic cloves and sprigs of thyme or basil if you like. Roast for 2 to 3 hours. They are ready when collapsed, jammy and slightly shrivelled at the edges. The oil and juices should be thick and sticky.

Tip: If you're short on oven space, roast at 150°C for 1.5 hours, but slower is better for depth of flavour.

Sieving to a Smooth Passata

Let the trays cool slightly. Tip everything, including the oily juices, into a large bowl. Pass the mixture through a food mill with a fine disc, or push it through a sturdy sieve using the back of a ladle. Discard the skins and seeds left behind. For a very smooth passata, blend the pulp in batches and pass it through the sieve again. Taste and adjust salt. If the passata seems watery, simmer it gently in a wide pan until it coats a spoon — but remember roasting already reduced it a lot.

You should have a pourable but thick sauce. A good rule of thumb: 5kg of fresh tomatoes yields about 2 litres of passata.

Bottling and Processing for Safe Storage

Tomatoes are borderline acidic, so if you plan to store passata at room temperature, you must acidify and process it. Sterilise jars or bottles by washing in hot soapy water, rinsing, then heating in an oven at 140°C for 20 minutes. Keep them hot.

Add 1 tablespoon of bottled lemon juice or 1/4 teaspoon of citric acid per 500ml jar before filling. Bottled lemon juice has consistent acidity; fresh lemons vary. Fill hot jars with hot passata, leaving 1cm headspace. Wipe rims, seal with clean lids.

Process in a boiling water bath: place jars in a deep pan, cover with water by at least 2.5cm, bring to a rolling boil and process for 45 minutes for 500ml jars (55 minutes for 1 litre). Turn off heat, leave jars in the water for 5 minutes, then lift out. Cool undisturbed for 12 hours. Check seals — lids should be concave and not pop when pressed.

Store in a cool, dark place for up to 12 months. Once opened, keep in the fridge and use within a week. If you'd rather not process, freeze the passata in bags or tubs for up to 6 months.

Flavour Variations and Kitchen Uses

Plain passata is a blank canvas. During roasting, add chilli flakes, smoked paprika, or a splash of balsamic vinegar. After sieving, stir through fresh basil or oregano. For a pizza sauce, reduce further with a little tomato purée.

Use your passata for:

• Simmering with garlic, olive oil and basil for a classic pasta sauce.
• Spreading on pizza bases or focaccia.
• Adding to soups, stews and casseroles for body and sweetness.
• Making shakshuka or baked eggs.
• Freezing in ice cube trays for single-portion flavour boosts.

There's no need to be daunted. Once you've made a batch, you'll never look at a tomato glut the same way again. The slow-roast method takes time, but it's largely hands-off — and the reward is jars of summer sunshine on your shelf all winter.