Every jar of olives leaves a parting gift. Once the last one has been speared, that cloudy, salty liquid tends to disappear down the sink without a second thought. It deserves better. Olive brine is salt, acidity and savoury depth in a single ingredient — a seasoning that already tastes of the thing you were cooking with. Treat it as a pantry staple rather than waste and it will sharpen your dressings, do the work of a marinade and turn a few odds and ends of vegetables into something worth eating. Here are eight ways to use it, plus a few notes on keeping it at its best.

Whisk it into dressings and vinaigrettes

The quickest win, and the one worth learning by heart. A classic vinaigrette is roughly three parts oil to one part acid. Swap the vinegar or lemon for olive brine and you get the acidity and the salt in one pour. Put three tablespoons of extra-virgin olive oil, one tablespoon of brine and a teaspoon of Dijon mustard into a jam jar, add a grind of black pepper, screw the lid on and shake hard until it turns thick and cloudy. Taste before you dress anything: some brines are far saltier than others, and you can always add more.

That dressing is especially good with bitter leaves such as chicory and radicchio, where the salt rounds off the edge, and with sliced tomatoes, which will release their juices into it. For something creamier, whisk a spoonful into mayonnaise or thick yoghurt with lemon zest and chopped dill. It makes a sharp, savoury sauce for roast salmon, cold chicken or new potatoes.

Use it as a marinade base

Brine does two jobs in a marinade: it seasons the food through, and its acidity starts to soften the surface. Build one with four tablespoons of brine, two tablespoons of olive oil, a crushed garlic clove, a few strips of lemon zest and a handful of chopped rosemary or oregano. Then match the timing to what you're cooking.

• Fish fillets — 20 to 30 minutes, no longer. The acid will start to firm and cure the flesh if you leave it sitting.
• Chicken thighs or pork chops — two to four hours in the fridge, then pat dry before grilling or roasting so they brown rather than steam.
• Firm tofu or halloumi — 30 minutes is plenty. Both take on salt quickly.
• Vegetables — chunks of courgette, pepper and red onion, half an hour before they meet a hot griddle pan.

Because the brine is already salty, hold back on seasoning the rest of the dish until you've tasted it.

Turn odds and ends into quick pickles

A jar with an inch of brine left in the bottom is a ready-made pickling liquor. Drop in thinly sliced red onion, cucumber, radish, carrot batons or a halved chilli, press them down so they're covered, and put the lid back on. An hour in the fridge gives you something crisp and sharp; a day gives you something better. If the brine doesn't quite cover the vegetables, top it up with a splash of white wine vinegar and a little water. If it tastes aggressively salty, add a pinch of sugar and shake again. Use a clean fork each time you dip in, and eat them within a couple of weeks while they still have bite.

Lift condiments, dips and pan sauces

This is the use that saves you reaching for the salt grinder. A spoonful of brine stirred into something bland will do more than a pinch of salt ever could.

• Into mayonnaise, with a little smoked paprika, for a quick sauce for fried fish or chips.
• Into Greek yoghurt with garlic and mint, as a dressing for roast aubergine or lamb.
• Into hummus or mashed avocado, to loosen the texture and sharpen the flavour.
• Into a hot roasting tin after the chicken comes out: splash in the brine, scrape up the sticky bits, add a knob of butter and you have a pan sauce in under a minute.

Season the cooking water

Pasta, new potatoes, bulgur, couscous and lentils all benefit from being cooked in salted water, and brine seasons more evenly than salt thrown in at the end. Replace about a third of the water with brine and taste as you go. Be more careful with rice: it absorbs most of the liquid it cooks in, so use roughly half brine and half water, or the finished bowl will be too salty to rescue. A splash in the water for steaming greens works nicely too.

Bake it into bread

Olive brine makes a soft, savoury focaccia or pizza dough. Replace up to half the water in your usual recipe with brine, then cut back the added salt — often to nothing at all. Don't go further than half, because a heavy salt load slows yeast down and you'll be waiting a long time for the dough to rise. Brush the top with a little more brine before it goes in the oven, along with your oil and rosemary, and the crust picks up a gentle olive flavour.

Put it in the drinks

A dirty martini is the obvious one: stir your gin or vodka with ice and add brine a teaspoon at a time until it tastes right, then strain. But it doesn't stop there. A dash in a Bloody Mary or a Virgin Mary deepens the tomato. A few drops in a glass of tomato juice with lime and celery salt makes a decent alcohol-free aperitif. And a brine ice cube dropped into a gin and tonic, or soda with lime, adds a salty edge as it melts.

Storing brine, and freezing what's left

Strain the brine through a fine sieve to catch any olive fragments, pour it into a clean jar with a lid and keep it in the fridge. Salt and acid help preserve it, but it is still a fresh ingredient: smell and taste it before each use. If it has turned fizzy, smells wrong or has grown anything on the surface, tip it out. If you can't get through it quickly, freeze it in an ice cube tray and drop a cube or two into stews, chillies, soups and sauces straight from the freezer — that's your eighth use, and a good habit to get into.

One last thing. Brine is salty by nature, so use it as a seasoning rather than a drink, and keep portions modest. If you are watching your salt intake for health reasons, speak to your GP or a dietitian before making it a regular part of your cooking.

Photo: VagelisDimas / Pixabay