Butter vs oil in baking
Solid against liquid, water against none, flavour against neutrality — three differences that decide which one a recipe can tolerate.
The short answer
Oil substitutes well where the fat was only lubricating and tenderising — many muffins, brownies and quick breads. It substitutes badly where the fat had to be SOLID: anything creamed, rubbed in or laminated depends on solid fat holding a shape, and a liquid cannot do it. Oil also brings no water, so it contributes no steam and no browning of its own.
Where they differ
| Dimension | First | Second |
|---|---|---|
| State at room temperature | Solid and plastic over a narrow range — it can hold a shape and hold air. | Liquid. It cannot hold air or form layers. |
| Water content | Roughly a sixth water, which becomes steam and contributes to lift and browning. | None. |
| Creaming | Works. Crystal structure traps air cut in by sugar. | Impossible. There is nothing for air to be held in. |
| Lamination and rubbing in | Works, and is the entire mechanism. | Impossible. |
| Keeping | Bakes firm as the fat resolidifies on cooling. | Stays softer for longer, because the fat never sets. |
| Flavour | Contributes considerably. | Neutral to mildly vegetal, depending on the oil. |
What this conclusion rests on
What oil can and cannot replace
Oil replaces butter’s lubricating and tenderising function and none of its others. It cannot be creamed, rubbed in or laminated, because those depend on a fat being solid and plastic — a state a liquid oil never occupies. Substituting by weight also removes butter’s water, so the formulation loses a liquid contribution and a steam contribution at the same time.
SPRINT 16 BACKFILL. This conclusion is the most consequential sentence on the page — it is what a reader acts on — and until this sprint the evidence instrument could not see it at all. The source defines the plastic state as a requirement for the techniques named and describes tenderising as lubrication, which is what supports both halves.
RecordedB. S. Ghotra, S. D. Dyal and S. S. Narine, Food Research International
The test that decides it
Ask what the recipe does with the fat before anything else. If it says cream, rub in, cut in or laminate, the fat has to be solid and oil will not work. If it says melt, or pours the fat in with the liquids, oil is usually a reasonable substitution.
That single question predicts the outcome better than any conversion ratio, and it is why "can I use oil instead of butter" has no general answer.
Related
Compares
The solid fat, and the one every creaming, rubbing-in and lamination method depends on.
Fat temperature
The comparison is really about fat STATE, which is the variable underneath it.