# Solid (and Liquid) Measuring Tips

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By Robert L. Wolke
Wednesday, December 21, 2005

I've been baking for years and I know that there is supposed to be a difference between liquid and solid measures. But what is the difference? It seems to be only in the larger measures, as I haven't seen liquid vs. solid measuring spoons. And what about wet stuff like sour cream and yogurt? Do I measure it as liquid or solid ?

There are two separate issues here: accuracy and convenience.

First of all, your observation that size matters is a sound one. For a tablespoon or less, neither accuracy nor convenience is compromised by using measuring spoons, whether of a solid or a liquid. If your half-teaspoon of salt is slightly rounded rather than level, it won't ruin your recipe. And if your tablespoon of olive oil dribbles over a bit, using the spoon is still easier than trying to hit the 1 tablespoon mark in a Tom Thumb measuring cup. So stick to your spoon measures. They dole out mere drops in a bucket anyway.

But when we get into the realm of cups, issues of convenience become important. A cup is a definite amount of volume: 8 fluid ounces or 14.44 cubic inches or 236.6 milliliters. A cup of stuff is a cup of stuff, then, no matter what the stuff is -- fluid or solid. The only reason I had to specify "fluid" ounces in my definition above is that our crazy American measurement system has three kinds of ounces: fluid, avoirdupois, and troy or apothecary. And they're all different. The first is an amount of volume, and the other two are amounts of weight, if you can imagine anything so perverse. (An avoirdupois ounce of a food is 28.35 grams, but gold and silver are measured in troy ounces at 31.10 grams each.) It's true that accuracy won't suffer very much if you measure a cup of flour in a glass measuring cup (a so-called "liquid" measuring cup). But it's easier to overfill an aluminum measuring cup (a so-called "solid" measuring cup) with the flour and then scrape off the excess by using a straight-edged tool such as a spatula or the back of a large knife.

Similarly, you can measure out a cup of olive oil in that aluminum "solid" measuring cup if you want to, but I bet you'll spill some, whereas if you overshoot the mark in the glass cup, you can always pour some out. The "liquid" measuring cup is simply more convenient for liquids.

That said, there are some minor issues of accuracy related to the use of cup measures. If you do try to measure out that cup of flour in a glass "liquid" measuring cup, you'll find it hard to get the flour's surface absolutely level at the 1-cup line (don't even try it with peanut butter), whereas a liquid's surface automatically levels itself. Scraping off the flour at the rim of an aluminum "solid" measuring cup is more reproducible, and hence more accurate.

What about those problematic semi-solids (or semi-liquids), such as sour cream and yogurt? They're liquid enough to form a flat surface in a glass measuring cup, yet solid enough to be scraped off at the rim of an aluminum measuring cup. So it's a draw, in both convenience and accuracy.

The ultimate solution? Don't measure your solid ingredients by volume. Throw away both your spoon measures and your aluminum cup measures, and measure all your solid ingredients by weight. That's what they do everywhere in the world, except for one country. Guess which one.

LABELINGO: Perspicacious reader Paul Rasmussen of Ann Arbor, Mich., bought a 12-ounce container of Kroger Spinach Dip. The ingredient list was 36 items long, with nary a hint of spinach to be seen until the very last word, where "dehydrated spinach" came after "sodium benzoate."

The FDA limits the amount of sodium benzoate preservative in foods to 0.1 percent. The amount of spinach in the spinach dip must therefore be less than that.

Robert L. Wolke (http://www.robertwolke.com) is professor emeritus of chemistry at the University of Pittsburgh. His latest book is "What Einstein Told His Cook 2, the Sequel: Further Adventures in Kitchen Science" (W.W. Norton, 2005). He can be reached atwolke@pitt.edu.

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