Weight vs. Volume

• Professional bakers' recipes are almost always measured by weight, because weights are consistent every time. Volume measurements can be trickier, because most dry ingredients can vary. For example, a cup of flaky sea salt usually weighs less than a cup of table salt, because it's not as dense. The same holds true for coarse sugar as opposed to fine sugar, and most recipes call for stickier brown sugar to be tightly packed into the cup for more accurate measurement. Flour is especially problematic, and measuring it by volume can be an exercise in frustration.

Compacting

• The problem with flour is that its fine, powdery texture traps a lot of air. When the flour is compressed much of that air escapes, leaving the flour dense and more tightly packed. Many old recipes call for the flour to be sifted before it's measured, restoring much of the air and reducing the amount of flour that's actually used. Modern flours are pre-sifted and often contain an anti-clumping ingredient, so that's not usually necessary any more. However, how you fill your measuring cup with flour makes a big difference.

Scooping vs. Spooning

• If you simply reach into the bag of flour with your measuring cup and scoop it out, you're compacting the flour just by measuring it. That means you might be adding more flour to your recipe than the author intended, which can make the result denser and tougher. The alternative is to spoon flour into your cup, then level it by swiping across the top with the back of a knife or some other straight edge. This measures one light, loose cup of flour without compacting it into the cup. The overall effect is to use less flour, keeping your baked goods more delicate.

Scale vs. Cup

• If you have a kitchen scale, you can try the experiment yourself at home. Use two identical measuring cups. Place one of them on your scale and "zero" the scale, adjusting it to compensate for the weight of the cup. Scoop one cup of flour out of the bag and shake it to smooth it, as many bakers do. Spoon flour into the second cup and level it with the back of your knife, then weigh each cup. The scooped cup can hold 25 to 40 percent more flour, more than enough to change your results drastically. If your recipe calls for "leveled" flour, ensuring a good result is worth the few seconds it takes.