How should I go about substituting canola or safflower oil for butter or shortening in baking recipes?
Liquid oils are ideal for baking, especially if you want to reduce saturated fats in your desserts. However, you must be ready for different end results than those you get from your standard recipe that uses butter or shortening.
The first thing you need to remember is that oil is 100% fat. Butter is mostly fat, with some milk solids and water. Shortening is mostly fat with some air whipped in. So, you need to use less oil than the amount of butter or shortening in a recipe. But, how much?
A good baker and I worked out this rule of thumb: For every 1/4 cup of solid fat required by a baking recipe, use 2 teaspoons less liquid oil. Let’s say your recipe calls for a 1/2 cup butter. To substitute oil, pour oil to the 1/2-cup level in a liquid measuring cup. Remove 4 teaspoons from the oil and discard or use for other cooking. Do not return it to the bottle. Add the measured oil to the dry ingredients before or with the liquid ingredients, depending on the recipe.
Back to the end results. As a general rule, butter or shortening will give you a drier, more delicate, crumb. Pie crusts made with butter or solid shortening are flaky, whereas pie crusts made with oil will be more like graham cracker crusts. Cake recipes in which oil is used are usually more dense and moist. If you are baking muffins or quickbreads, oil is a perfectly acceptable choice for moist results.