Two bottles sit side by side on the supermarket shelf, both green, both promising Mediterranean sunshine, and one costs nearly twice what the other does. The difference is not marketing fluff. It comes down to how the oil was extracted, what was left in it, and what you plan to do with it once you get it home. Here is how to tell the two apart and decide which one belongs in your cupboard.

What Separates the Two Bottles

Extra virgin olive oil is about as close to fruit juice as a cooking fat gets. Ripe olives are crushed, the paste is spun or pressed, and the oil is separated mechanically. No heat above roughly 27°C, no chemical solvents, no refining. Everything the olive brought with it — the aroma, the colour, the bitter and peppery compounds that give it character — stays in the bottle.

Regular olive oil, often sold simply as "olive oil" or "pure olive oil", is a blend. Most of it is refined oil, treated to strip out flaws in flavour and acidity, with a small amount of virgin oil stirred back in for taste. It is not fake and it is not inferior for cooking. It is simply a different product with a different job.

The main grades you will meet in UK shops:

• Extra virgin olive oil — mechanically extracted, free acidity below 0.8%. The boldest flavour and the highest levels of natural polyphenols.
• Virgin olive oil — the same process, with acidity allowed up to 2.0%. Milder, sometimes a little rougher, often good value.
• Olive oil or pure olive oil — refined oil blended with a little virgin oil. Neutral, pale, dependable.
• Light or extra light olive oil — a description of flavour and colour only. It has the same calories as every other olive oil on the shelf.
• Olive pomace oil — extracted from the leftover olive paste, then refined. Cheap and bland, best kept for the deep fryer.

Smoke Points, Without the Panic

A lot of advice online makes extra virgin sound too delicate to cook with. In practice, a decent extra virgin smokes somewhere around 190–210°C, while refined olive oil sits closer to 230–240°C. Home roasting usually runs at 180–200°C, shallow frying at 170–190°C and deep frying at 175–190°C. That means extra virgin copes perfectly well with most of what happens in a domestic kitchen.

Where refined oil earns its place is long, hot, repeated frying — chips, doughnuts, a big batch of onion bhajis — and any dish where you do not want the oil to announce itself. Refined oil is also more economical when you are pouring a litre into a pan.

Two practical habits matter more than the number on the label. First, oil degrades every time it is heated, so a bottle that has been used for three fry-ups will smoke earlier than a fresh one. Second, wipe the pan between uses; burnt specks left behind will taint the next batch far faster than the oil itself will.

Flavour: The Real Dividing Line

Fresh extra virgin tastes of something. Depending on the olives, the region and the harvest, expect grass, tomato leaf, artichoke, green almond or a hint of banana skin. A peppery catch at the back of your throat and a faint bitterness are positive signs — they point to the polyphenols that make the oil worth buying. Oil that tastes of nothing, candle wax, cardboard or old nuts is tired, badly stored or simply poor.

Refined olive oil is neutral by design. That is useful in a cake batter or a marinade where you want the herbs and spices to lead, and disappointing on a plate of tomatoes where the oil should be part of the seasoning.

Freshness beats grade every time. A supermarket own-label extra virgin from the most recent harvest will out-taste a tired premium bottle from two years ago. Look for a harvest date rather than trusting a best-before stamp alone.

Matching the Bottle to the Job

• Dressings, dipping and drizzling: extra virgin, always. Whisk it with lemon juice, salt and a little mustard and you have a dressing that needs nothing else.
• Roasting vegetables and traybakes: extra virgin. The heat softens the pepperiness and leaves a rounded, savoury note behind.
• Shallow frying, omelettes, garlic in a pan: either works. Use extra virgin if you like the flavour it adds, refined if you do not.
• Deep frying: refined olive oil or a neutral high-heat oil. Cheaper to replace and slower to break down.
• Baking: regular olive oil in plain sponges and breads; extra virgin in a rosemary, lemon or chocolate cake where the flavour has somewhere to go.
• Marinades: regular for spiced lamb or chicken, extra virgin for delicate fish and grilled vegetables.

Reading the Label Like a Shopper

Harvest date first

Olive oil is a fresh product, not a wine. Most bottles are at their best within 12 to 18 months of harvest, and quality fades once opened. If a label shows only a best-before date two years out, you are guessing.

Origin and wording

"Produced in" tells you where the olives were grown and pressed; "bottled in" tells you almost nothing. A blend of EU and non-EU oils is legal and often fine, but it will vary from batch to batch. Single-country or protected origin bottles (PDO or PGI) tend to be more consistent, and usually cost more.

Packaging

Dark glass or a tin protects the oil from light, which is one of its fastest destroyers. Clear glass on a bright shelf is a warning sign. At home, keep the bottle in a cool dark cupboard away from the hob, sealed tightly, and use it within a few months of opening.

One sensible note on health: olive oil is a fat and calorie-dense whatever the grade, and the well-publicised benefits tied to Mediterranean-style eating come from the whole pattern of meals rather than one bottle. If you have a medical condition or take medication, speak to your GP or a registered dietitian before making significant dietary changes.

A Simple Shopping Plan

You do not need six bottles. Buy two and use them properly. Choose a fresh, single-origin extra virgin in dark glass or a tin for dressing, finishing and roasting, and a larger, cheaper bottle of regular olive oil for frying, baking and marinades. Taste the extra virgin on a spoon before you commit to it — if it has no perfume and no pepper, put it back. Store both away from heat and light, and buy smaller bottles more often rather than a giant one that sits half-used for a year.

Photo: RDNE Stock project / Pexels