Is it absolutely necessary to use a dry measuring cup for dry ingredients and liquid measuring cup for liquid ingredients?
So you need to measure some all-purpose flour, but all of your dry measuring cups are in the dishwasher. Can you use a liquid measuring cup? We conducted some tests to determine if it's necessary to use the appropriate measuring vessel for dry and wet ingredients.
To demonstrate how each type of measuring cup fared, we asked 18 people, both cooks and noncooks, to measure 1 cup of all-purpose flour in both dry and liquid measuring cups. We then weighed the flour to assess accuracy (a properly measured cup of all-purpose flour weighs 5 ounces). With the dry measuring cup, the measurements were off by as much as 13 percent. This variance can be attributed to how each person dipped the cup into the flour; a more forceful dip packs more flour into the same volume. Measuring flour in a liquid measuring cup, where it’s impossible to level off any excess, drove that variance all the way up to 26 percent.
The same people then measured 1 cup of water (which should weigh 8.345 ounces) in both dry and liquid measuring cups. The dry cup varied by 23 percent, while the liquid cup varied by only 10 percent. In this case, it was much easier to gauge the volume of water in the liquid measuring cup, as its transparency allowed measurers to see when the meniscus—the bottom of the curved surface line of the liquid—had touched the 1-cup line. There was a greater variance when measuring water in a dry cup because it was so easy to overfill, as the surface tension of water allows it to sit slightly higher in this type of vessel.