I have a question on protein amounts. sometimes a recipe calls for a flour with 13-14 percent protein. How is that converted or measured if the bag (ie King Arthur Bread Flour) says 4% per 1/4 cup
If you are looking for accuracy on the protein content of a given flour based on the Nutrition Facts for that flour, you are unlikely to get it. The reason is that the FDA allows rounding of certain numbers. For example, if you look at the Nutrition Facts for the King Arthur Bread Flour (KABF) at http://www.kingarthurflour.com/shop-img/labels/1364924328221.pdf
, you will see that the serving size of that flour is 1/4-cup (the FDA requires that the serving size be recited as a household measure, in this case, 1/4-cup) and the weight is given as 30 grams. You will also see that the protein content for that serving size is recited as 4 grams. Under FDA rules and regulations, the protein content of a sample is required to be reported to the nearest gram. Similarly. the weight of the sample that corresponds to the household measure is required to be stated to the nearest whole number. So, as you can see, the possible range of protein values can be quite wide and result in a percentage range that is similarly quite wide. If the actual protein content was precisely 4 grams and the serving size was precisely 30 grams, then the protein content would be 13.33% (4/30 = 13.33). King Arthur itself says that the protein content for the KABF is 12.7 +/- 0.2%. That is the number you want to use if you are after accuracy, not the Nutrition Facts.