Greasing the bottom of an aluminum baking pan before putting it in the oven is generally not necessary. Aluminum pans are often considered non-stick, and many baked goods won't stick to them during the cooking process. However, there are a few factors to consider:
Type of Recipe: Some recipes, particularly those with high sugar content or sticky ingredients, may benefit from greasing the pan to ensure easy removal after baking.
Extra Insurance: Greasing the pan can provide extra insurance against sticking, especially if you're unsure about the specific non-stick properties of your pan.
Personal Preference: Some people prefer to grease the pan out of habit or to be cautious, as not all aluminum pans are made with a non-stick coating.
If you choose to grease the pan, you can use butter, oil, or a non-stick cooking spray. Simply apply a thin and even layer to the bottom and sides of the pan. Keep in mind that excessive greasing or using too much oil/butter can lead to uneven baking or even affect the texture of the final product, so use it sparingly.
If the recipe specifically calls for greasing the pan, make sure to follow those instructions. Otherwise, for many standard baking recipes, you can get away without greasing an aluminum pan. Just ensure it's clean before using, and any non-stick properties should generally be sufficient for most baking needs.