I'll confess that while I do own a flour sifter, it usually stays in the back of one of my kitchen drawers, unused. Recipe instructions for baked goods can be all over the map when it comes to sifting — some insist that you sift multiple times, while some don't have you do it at all. Is the process of sifting really necessary?
What Does Sifting Flour Do?
Sifting is a process that breaks up any lumps in the flour and aerates it at the same time by pushing it through a gadget that is essentially a cup with a fine strainer at one end. Sifted flour, which is much lighter than unsifted flour, is easier to mix into other ingredients when forming a cake batter or making dough.
When flour is sifted with other dry ingredients, such as cocoa powder, this helps to combine them evenly before they are mixed with other ingredients. Sifting flour also means you are more likely to measure consistently because the condition the flour starts out in, packed or not packed, doesn't really matter since you'll be sifting it.
When Should You Sift Flour?
Sifting flour used to be necessary to separate out things like bugs or chaff (husk of corn or seeds). Commercial flour, however, is refined enough now that this process is generally unnecessary in ordinary, everyday baking. I fluff up my flour with a spoon before I measure it out, then just use a whisk to combine my dry ingredients for things like cookies, muffins, most cakes, quick breads, and pie doughs.
There are times, however, when certain recipes actually benefit from sifted flour. The flour in cakes with a very light, delicate texture like genoise, angel food, or sponge should be sifted to eliminate and prevent lumps that would weigh down the batter.
If your flour has been sitting around for awhile and seems very tightly packed, it might also be a good idea to sift it before using it so that you're not measuring out overly packed cups.
Finally, sifting flour over a work surface when you're about to roll out or knead dough can be a good idea if you want a thin layer of flour, since adding too much additional flour to your dough can dry or toughen it.
How Do You Sift Flour?
If your recipe calls for sifting and you've decided to follow it, here's how to sift:
First, check the wording of your recipe. If your recipe calls for "X cups sifted flour," that means that you should sift a bunch of flour, then measure out the amount called for. If the recipe says, "X cups flour, sifted," then you can go ahead and measure out the flour, sift it, and use that same amount.
Lastly, a sifter is a useful gadget if you sift frequently, but if you don't have an actual sifter, a fine-mesh strainer can also do the trick.