Calibration in real life

[Big Jim]

Ran into an amusing situation and thought it worth passing on. My wife and I are both bread bakers. Among serious bread hobbyists there is a trend toward weighing the ingredients instead of using volume measures. King Arthur Flour sells a converting scale made by Escali. Using a conversion code from a provided chart you can switch between volume and weight. Seemed like a great idea so I bought one. When it arrived I tried to demonstrate how it worked by using a measured cup of water then converting it. I used a Pyrex 2 cup glass measuring cup as the receiving vessel and a Pyrex 1 cup glass measuring cup as the delivery vessel. I set the scale on grams, set the larger cup on the scale are tared it out, then poured in a measured 1 cup into the larger cup where it also read 1 cup. I pressed the volume button, punched in the code for water, 61, and to my surprise it read 3/4 cup. I repeated it several times with the same results.

This morning I called Escali Technical Support and he walked me through checking out the scale. First we checked the accuracy of the scale using nickles. US nickles weigh 5 grams each. The scale was accurate with nickles. Then we did what was done before with the Pyrex measuring cups with the same results as before. Then we weighted out 240 grams of water into the same larger Pyrex measuring cup. 240 grams is the correct weight for a cup of water. It showed 1 and 1/8 cup on the Pyrex cup. I repeated it with the Pyrex 1 cup and it also read 1 and 1/8 cup. So I took a stainless steel 1 cup measuring cup and tared it out, then poured 240 grams of water into it. It filled it right to the brim and the scale showed 1 cup.

It appears that Pyrex glass measuring cups don't have NIST calibration traceability. What a shame for a well know scientific glass provider.

 

[hogheavenfarm]

I always thought liquid measure and dry measure were different in non metric systems.

 

[John Predmore]

Hence the emphasis on weight instead of volume.

Pyrex is a trademark of Corning Glass. You didn't indicate who was the manufacturer of the measuring cup, but the manufacturer is responsible for the volume markings.

My wife reminds me there are different measuring cups for dry and wet ingredients. This article explains the volume is the same, the real difference is the technique of filling the cup. You decide what you believe.

I remember as a wee lad, my mother had me sifting flour before she did any baking. Now the grocery store only sells pre-sifted flour. But I know powder in any container can settle with time and the density will change. Another good reason to measure by weight. But if you use a conversion factor to convert the recipe amount to weight, how do you know your conversion factor is correct for the powder you use?

 

[Ninja]

When I get recipes that look interesting, I follow them, then make them again with tweaks to make it better if I can...
All are recorded in weight using an electronic balance.

Once I started cooking with a balance, all of the recipes came out the same every time... I won't go back to volume again anytime soon...