Olive oil
A liquid oil chosen for flavour rather than for function — which makes the grade question a flavour question, not a baking-performance one.
Also called extra virgin olive oil (INTERNATIONAL); EVOO (US); virgin olive oil (INTERNATIONAL)
Structurally, olive oil is a neutral liquid oil. It is liquid at kitchen temperatures, it cannot be creamed or laminated, and it lubricates. Everything in the vegetable oil record applies to it unchanged.
What it adds is flavour, and that is the only reason to choose it. In focaccia, olive oil cake, savoury quick breads and some biscuits the flavour is the point. In a vanilla sponge it is an intrusion.
THE GRADE QUESTION IS ABOUT TASTE AND HEAT, NOT ABOUT STRUCTURE. Extra virgin is the least processed grade and carries the most flavour compounds; refined olive oil carries fewer and is blander. Neither behaves differently in a batter. The common warning against baking with extra virgin concerns its lower smoke point, which is a frying consideration — the interior of a cake does not exceed the boiling point of water, and a bake at ordinary oven temperatures does not take the oil anywhere near smoking. What CAN happen is that heat drives off the volatile compounds you paid for, which is an argument about value rather than about safety.
Some bakers find strongly peppery oils turn bitter in sweet bakes. That is a real and repeatable objection to particular oils rather than to the grade, and it is why a mild oil is usually the better choice in a sweet cake.
What changes if it is left out
Replacing it with a neutral oil changes the flavour and nothing else. Replacing it with butter changes the structure as well, because butter is solid and brings water.
Follows from olive oil being functionally a liquid oil, recorded above.
RecordedFollows from evidence recorded elsewhere on BakeHQ
Related
What it does
Flavour contribution
The only reason to choose it over a neutral oil. Structurally the two are interchangeable, so flavour is not a bonus here — it is the entire decision.
Gluten inhibition
Identical to any other liquid oil. Nothing about being olive oil changes the tenderising route.
Used in
Brushed between sheets in many traditions; butter in others.
Compared in
Olive oil vs vegetable oil in baking
One side of the comparison.