Tuesday, April 19, 2016

OK, how big is a tablespoon, REALLY?

One of the handiest cooking factoids in our crazy US measurement system is that there are 4 tablespoons in a quarter cup.  If you are doubling a recipe for a sauce that calls for 2 tablespoons of flour, don't measure 4 tablespoons, just measure 1/4 cup and you're all set.

So I was a little surprised when I was looking at a source I consider reliable (Samuel Fromartz's In Search of the Perfect Loaf, p. 87) to see "Mix 3 tablespoons (30 grams) lukewarm water..."  Now, "everyone knows" that a tablespoon is 15 ml, and 1 ml of water weighs a gram, so 3 tablespoons of water should be 45 grams.  OK, precision is overrated in cooking, but it is more important in baking, and this is a 50% difference (45 being 50% more than 30), and that is actually significant.

1 tablespoon "=" 15 ml

Luckily, before I sent a know-it-all email to Mr. Fromartz, I decided to make sure, and when I weighed a tablespoon of water on my lovely digital kitchen scale (more on that next post) it was 10 grams. Oops. The plot was thickening. Three tablespoons got me up to 31 grams, so maybe a bit more than 10 grams. Googling "one tablespoon of water to grams," the top few hits are all say 15, you get to a precision calculator whose default is "5 digits after the decimal point" (OK, that is insane, we are not detecting gravitational waves here), but when you turn it down to a respectable "1 digit after the decimal point" it says 14.8, which is acceptable (though incorrect), for reasons below. The next hit says 15.00 which is not acceptable.  If you are going to stick in places after the decimal point, you cannot round up.

You have to get to the next-to-last entry on the first page before you find someone who actually tried it.  They say 12 grams... and interestingly, the scale they photographed says 11 grams... and the page I first saw, on the same site, seems to have the same photo, and that page says 11 grams.  But 10-11-12? This is getting into a more acceptable range of accuracy. Also, their tablespoon looks like a table spoon, not the Precision Measuring Instrument I use, pictured above.

This left me with only one question, which I will abbreviate: WTF!?

So I got out my 1/4 cup measure, stuck it on my scale, and measure out 4 tablespoons of water. Here's what I saw:



You can see 41 grams, right in line with Sam Fromartz, and if you look carefully, you can see that the measuring cup is nowhere near full.  (Also, when I first did this, I made the tablespoons as full as I could, which meant, I think, that there was a meniscus of water sticking up above the full mark.  That was 50 grams of water, or 12.5 grams per tablespoon, still in line with the web page where they actually measured it.  But in terms of everyday cooking it was still Sam Fromartz all the way.)  When I filled the 1/4 cup measure to the top, it was 56 gm, which is about what it should be, see below.

OK, so how many (of my) tablespoons are actually in 1/4 cup? To do that I needed to measure a non-liquid.  Flour is too compressible to get a reliable answer, so I used salt. The answer?




Not 4... but you knew that.  And of course I'm saying "my tablespoons" because I now have zero confidence that there is really any such thing as a standard tablespoon.




More than 5.  Really?




Less than 6.  Phew!  I scooped up the overflow, which was 2 teaspoons, or 2/3 tablespoon, so it appears that there are 5 1/3 of my tablespoons in 1/4 cup.  I say "appears" because I am not convinced at this point that there will be 3 of my teaspoons in one of my tablespoons—which is what there should be—if I measure it carefully.  But to stay sane (or, I should say, as sane as possible), I'm not going to do that.

In medical school we used metric units, but when you get to pediatrics they do talk about ounces of formula, so you need to convert.  If you ask a pediatrician how many grams in an ounce, they will say 30, because medicine is maybe a little more precise than cooking but not all that much.  Now there are 8 fluid ounces in a cup, so 1/4 cup is two fluid ounces, so if the pediatrician was right, my scale should have read 60 grams when I filled the 1/4 cup measure with water.  (A fluid ounce of water should weigh one ounce, right? So I thought, but, uh, no, though pretty close. Apparently we were thinking of Imperial fluid ounces. You knew that, right?)   But my scale said 56, what's up with that?

If you ask a pot smoker how many grams in an ounce they will say 28, because they are paying for the stuff. If you ask a drug dealer, they will probably say 28.35 because they are even more highly motivated to precision.  So it was always interesting in med school when the professor said, "How many grams in an ounce?" and the folks who usually knew all the answers were stumped, but the hand shoots up of the kid who is not considered the sharpest knife in the drawer, and he says, proudly, "28!"  "Well, 30, actually," says the professor, incorrectly. I felt bad for that guy but I felt like I knew him a little better after that.

So 1/4 cup is really 2 ounces, and an ounce of water is really pretty much 28 grams, so 2 ounces of water is 56 grams, which is what my scale said, so that part checks out.

The take-home message?  Cook with a scale, like the europeans do, and use grams.  (More on that in my next post, if I ever write it.)  All my European friends would be shaking their heads about how crazy we Americans are to cook this way, except that they are too busy shaking their heads about how crazy we are to have so many guns. Well, maybe we can't do anything about the guns, but we can do something about cooking.  I haven't locked up my measuring cups yet, though.

But if anyone can shed some light on how this state of affairs came to be, I'd love to know. I am confident that it's not because I happen to have a bad tablespoon...

2 comments:

  1. That's the trouble with volumetric (eg cup) measurements: A cup of flour weighs a different amount to a cup of water etc. Go metric and buy electronic scales.

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    1. I completely agree! (and am planning to write a post on exactly that subject) Not to mention the fact that a cup of flour weighs a different amount from another cup of flour...

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