I went looking for the tests to determine protein/gluten content and found them, at the Correll website. I have cut and pasted below (with some slight editing) the two tests commonly used. They are basically the ones I briefly discussed in my previous post on this thread:
"The farinograph is a small mixer connected to a graphing device. From mixing a small batch of test dough it charts, among other things, the water absorption capacity and mixing tolerance of a flour. A flour’s water absorption capacity is the percentage of water needed to produce a dough of a given consistency. Generally, the higher the water absorption capacity, the better the flour.....Another test, which requires no equipment and has been used for years by bakers, is the gluten ball test. It’s used for comparing the protein levels of different flours, and can easily be done in a pizzeria. Here’s how to do it.
Measure out exactly 6 oz of each type of flour being tested. Mix each flour with enough water (approximately 3 oz) to make a stiff dough, knead it for five minutes, then allow it to rest for fifteen minutes. After that, wash each dough ball under a stream of cool water, kneading constantly until the water runs clear and all that remains is a rubbery mass. This is pure gluten. Place the ball on a paper towel for one minute, to drain off excess water, then weigh it. The heaviest ball indicates the flour with the most protein.
For further comparison, form each gluten piece into a smooth ball and place them on a pan, allowing at least 3 inches between them. Bake them in a hot oven (450 to 500 degrees F) for about an hour. The balls will expand. After baking compare their size. Generally speaking, the largest ball indicates the flour with the most and, possibly, highest quality protein."