The technology of baking requires specific steps that ensure that baked goods rise properly with the correct texture. Cookies, brownies and quick breads, for example, often stipulate that ingredients be mixed separately: dry in one bowl and wet in another. Failure to mix the ingredients in this manner can alter the finished product and completely change the taste. If your recipe instructs you to mix the ingredients separately, don’t skip this step.
Recipes that call for separation of wet and dry ingredients require ingredients such as water, oil, milk, butter, buttermilk and eggs to be mixed together in one bowl. Powders like flour, sugar, salt, baking powder, baking soda and spices get well mixed in another bowl. If sifting is required, it is done at this time as well. After you mix both sets of ingredients, you combine them, but not all at once.
One reason for separating the ingredients is to ensure that the dry mixture has time to completely incorporate itself into the liquid mixture, instead of forming indestructible lumps. Some recipes will require that you add the dry mixture into the liquid mixture in several parts, and others may require you to alternate the wet and dry ingredients. In this case, start with dry and end with dry so the flour fully incorporates itself into the emulsion. If you were to just dump all the ingredients into the bowl and mix, it will never mix properly because the mixture won’t have time to incorporate properly.
Another reason some recipes require separation is because the more you mix dough, the more long, tough strands of gluten you form. Gluten strands also form spontaneously in moistened wheat flour. Gluten is responsible for giving yeasted bread its firm structure -- that's why bread recipes call for kneading or for resting overnight. If you were to throw all of the ingredients into a bowl and mix, it would require so much mixing to fully distribute everything throughout the dough that the finished product would be very tough and chewy. Separating the wet and dry ingredients allows each set of ingredients to be mixed thoroughly so that you can combine them with the least possible mixing in the least possible span of time.
If you forget to separate the ingredients, there’s no need to throw out your work. The finished product may be a bit tough or chewy, and the texture may not be completely normal, but it is still edible. If you’re working on a dessert or other project for a family get together or event, you might want to make a second batch using proper technique. Otherwise, you could modify the finished product to make it more enjoyable. If your cookies are chewy, chop them up and use them in a cookie sundae. If the quick bread is tough, toast it for croutons or French toast, or use it in bread pudding.