What grains (and in what ratios) go into a nine-grain flour?
There is no fixed set of grains or ratios that define nine-grain flour. It is just meant to generically suggest "uber-healthy". Some things you may want to use include: whole wheat, rye, triticale, barley, oats, buckwheat, spelt, emmer, millet, flax, etc. Most so-called 9-grains or 12-grain etc will "cheat" and include wheat in multiple forms, like wheat flour, cracked wheat, vital wheat gluten and so forth. In any case, if you are going to use it for bread, you'll probably want at least 50-75% wheat flour so that there is enough gluten to successfully rise. The rest can be in any proportion that pleases you for taste or nutritional purposes.