250ml, 500ml or 3 litres: which size for your kitchen

Choosing a size looks like a question of price, and most people decide by comparing cost per litre. That is the wrong sum, because it assumes all the oil in the container will be used in equally good condition. It will not.

The real question

How long will it take you to finish the container after opening it? Opened olive oil is at its best within about two months. After that the flavour starts to fade, even though the oil remains perfectly safe.

So the right size is the one you finish inside that window. Anything larger means paying for oil that will have gone flatter before you reach it.

Rough estimates by use

• Salads and finishing only, one or two people: 250ml
• Salads plus sautéing a few times a week: 500ml
• Daily cooking for two to four: 500ml, or two 500ml bottles
• Daily cooking for a large family: two 500ml bottles or more
• Caterers, cafés, shops, or a household cooking for many every day: 3 litres

Why two small bottles beat one large one

This is the part rarely explained on a shelf. Olive oil degrades on contact with oxygen, and every time you pour, air moves in to replace what came out.

A bottle down to its last quarter is mostly air sitting on top of your oil. A one-litre bottle spends twice as long in that state as a 500ml does.

Two 500ml bottles give the same volume, but the second stays factory-sealed until the first is finished. You get a litre of oil with only one bottle exposed at a time.

When 3 litres makes sense

A large tin gives the lowest cost per litre, and it makes sense if you will genuinely finish it within a few months. But it asks for one extra habit: decant into a small bottle for daily use and keep the tin sealed.

Opening and closing a three-litre container several times a day lets air in each time, and a half-empty tin holds a litre and a half of it. Decant once a week into a 500ml bottle, and the tin stays effectively sealed for most of its life.

If you have not tried it before

Start small, even though the price per litre is higher. Fresh extra virgin olive oil has an assertive taste — peppery at the back of the throat, slightly bitter — and it is not a taste everyone takes to immediately.

Better to find that out from a 250ml bottle than from a three-litre tin.