Swapping butter for olive oil: ratios and limits

Butter and olive oil are not the same thing, and swapping one for the other is not simply changing a name in a recipe. Butter contains water and milk solids; olive oil is pure fat. That difference changes the ratio.

The base ratio

Use roughly three quarters as much olive oil as the butter a recipe calls for. If the recipe asks for 100g of butter, use about 75ml of olive oil.

The reason is that butter is roughly 80% fat, with most of the rest being water. Using the same volume of oil means adding more fat than the recipe intends, and the result comes out greasy.

For cooking on the hob

Here the swap is easiest, and often an improvement. Butter burns at a relatively low temperature because its milk solids scorch; olive oil does not have that problem.

• Scrambled eggs and omelettes — olive oil gives a softer result and does not burn
• Softening onions and vegetables — swap straight across, one for one is fine
• Oven-roasted vegetables — olive oil is better, because it does not scorch at oven temperatures
• Toast — olive oil with a pinch of salt in place of butter

For baking

Baking is trickier, because butter does two jobs: it adds fat, and it adds structure. Solid butter traps air when it is creamed with sugar, and that air is what lifts a cake.

Olive oil cannot trap air that way. So the substitution works well in some bakes and not in others.

• Works: moist sponge cakes, chocolate cake, muffins, brownies, banana bread
• Works: bread and pizza dough, where olive oil is traditional anyway
• Does not work: short pastry, which needs solid fat
• Does not work: biscuits that have to hold their shape
• Does not work: icing and buttercream

The flavour

Extra virgin olive oil tastes of something, and that taste shows up in a bake. In chocolate cake or banana bread it disappears behind the other flavours. In a light vanilla sponge, you will notice it.

That is not necessarily a problem — olive oil cake is a traditional dish in parts of the Mediterranean, and the flavour is the point. But know what to expect before swapping it into a family recipe.

For baking, some people prefer a milder-tasting olive oil. Fresh oil high in polyphenols brings a more pronounced peppery note, which suits some cakes and clashes with others.