Reader Sandra writes in to ask about protein (gluten) percentages:
(King Arthur) has that sort of information on their website somewhere, I’m sure (I’ve never gone hunting for it), but what about standing in the aisle of the grocery store? Is there a way to look at the nutritional information label and figure out the percentage?
I believe you can estimate the protein levels of various flours by the nutrition labels, which are required by law on every packaged food product these days. Taking this as an example, you can see that the amount of protein is listed in grams per serving close to the bottom there (13), and the total number of grams that make up a serving (125) up at the very top.
Divide 13 by 125 and multiply by 100 (if my remedial grade school math serves me correctly) and the result is 10.4, which is entirely plausible for this sample flour, which is probably an all-purpose. I tried the same thing with my bags of self-rising biscuit and whole wheat flours and got 6.7 and 11.8 respectively. That’s right in the target zones for those kinds of flours. Of course the best information will always come straight from the manufacturer, since as I said, there are some non-gluten proteins in some flours, especially those that contain more of the bran and germ. But this system should do in a pinch!