When A Cup Isn't A Cup


30 April 2009

I write recipes using weights, usualy metric. When I use a recipe, I prefer it to be in weights, because it's always seemed to me to be more precise. It's not *bad* to use volume to measure solids, obviously. But it can explain why your recipe isn't working out right.

Some solids don't measure easily. Take shortening, for example - it's a mess to scoop into the measuring cup, you have to make sure all the air has been pushed out, etc. But that's the least of our problem.

The real problem comes from ingredients that can change volume depending on how loose or compact they are. Brown sugar and flour are good examples. When you read recipes that involve brown sugar, you will often see "packed", or "firmly packed", or no mention of any packing made. This does cause a problem because the amount of brown sugar will vary wildly depending on how loose or packed it is in the measuring cup. Same thing with flour.

Here's a little demonstration, measuring a cup of flour, then weighting it, let's see the difference.

Three mounds of flour

(straight out of pack)
(with a spoon)
140grams 125grams 195grams
  Short 11% Extra 39%
One cup of flour weighs differently depending on how packed it is

Full cup of flour

I measured a cup of flour, using a 1-cup stainless steel container. I filled the container, then used a spatula to even the top.

Mounf of flour, one cup measured out of the box.

The first cup I measured was the flour, somewhat compacted, straight out of the bag. I then used an electronic scale to measure it. The weight of one cup of flour straight out of the bag was 140grams.

Mound of flour, one cup, measured after sifting

The second cup I measured was the flour, after sifting it once. The weight of one cup of flour, sifted, was 125grams. Or 11% less than the first cup!

Mound of flour, one cup measured after being compacted

For the third cup, I used the back of a soup spoon to pack the flour in the measuring cup. The weight of one cup of flour, compacted, was 195grams. Or 39% MORE than the first cup.

So, with such differences, it's not surprising that your wonderful cookie recipe turns out like little bricks when someone else makes it!

It's not a huge problem in most cases. It's not WRONG to use volumes to measure ingredients. It is just something to be aware of when using volume to measure such dry ingredients.


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