Butter vs. Oil in Cake: What Is the Difference?

The first difference between the two fats is their composition. Butter is not pure fat: although most of it is fat, it also contains water and milk solids. Oil is almost entirely fat. This difference has an immediate effect: butter adds some water and protein to cake. That water turns to steam in the oven and helps with rising, while the protein speeds browning on the surface. The water content of butter varies by brand, so the same recipe can turn out differently with different butter.

The second difference is consistency, and it has a greater effect. Butter is solid but pliable at room temperature; when creamed with sugar, it incorporates air and builds the cake’s structure from the start. Oil cannot do this because it is liquid and does not trap air. In oil-based recipes, all the rising is left to the leavening agent and eggs, and there is no creaming step. Some recipes use melted butter, but in those, butter acts like oil.

The third difference appears in the finished cake’s texture. Oil coats the flour particles more completely and limits gluten development, resulting in a softer, moister crumb. Since oil does not solidify in the cold, cake made with oil stays soft even in the refrigerator. Butter cake firms up as it cools and holds its shape more upright when sliced; bring it to room temperature before serving. For this reason, cakes meant for travel or to be kept until the next day are often made with oil. If freezing a butter cake, slice and wrap the pieces individually so you can thaw only what you need.

Butter has a clear advantage in flavor, and no liquid oil can replace it. On the other hand, in chocolate, spiced, or fruit cakes, the recipe’s own flavor is already strong, so oil makes little difference. If using olive oil, choose a variety with a mild aroma. Oils such as sunflower and corn oil are neutral oils and the safest choice for most cakes. Aromatic oils such as hazelnut and walnut oil are used in small amounts alongside a neutral oil.

If substituting, do not use the same amount. Because some of butter’s weight is water, using an equal weight of oil raises the fat content and makes the batter heavy. As a practical rule, use about four-fifths of the butter’s weight in oil and make up the remaining liquid with milk. In the other direction, use extra butter and reduce the liquid in the recipe somewhat. In both directions, make the first attempt in a small pan, since the texture difference cannot be predicted from the measurements alone. Using both butter and oil in equal halves in the same recipe is also common: butter provides flavor, while oil provides moisture.