I am trying to use more alternative flours in baking but haven't had much luck with these two. Do they need to be mixed with other flours, or can I use them by themselves?
Try including the soy flour along with regular APR when baking, I use it while making Indian rotis & paratha for my kids as an added protein source.
These flours don't contain any gluten, which is what holds "normal" baked goods together. You can find recipes that only use these flours, but they won't be quite like the baked goods you're used to. (Bibingka is an excellent dessert that sometimes uses only brown rice flour; I can give you my recipe for that later today if you'd like.)
When you mix brown rice and soy flours with other flours, you can have excellent results. If you're using regular all-purpose flour, you can use up to a 1:1 ratio with success. Don't go beyond that with the brown rice and soy flours or your baked goods will really change in texture and have trouble holding together.
If you're using brown rice and soy flours because you're gluten-free, I recommend using sweet rice flour as your binding flour. I use this with brown rice flour at a 1:1 ratio and it works perfectly. Add 2 Tbls tapioca starch to that and you'll have no complaints about your products.
Take a look at my recipe for Cardamom Banana Bread for an example of how brown rice, sweet rice, and tapioca starch work together.
By the way, my Cardamom Banana Bread uses amaranth flour in it as well. You can use brown rice or soy flour in its place and it works exactly the same. (With the soy flour producing a denser, usually slightly drier loaf.)
Brown rice flour also makes a nice crispy coating for oven fried meat and fish. I season it and use it very similarly to corn meal on these proteins. bake at 420 f. until the protein is cooked.
If you are going an gluten-free baking, a mix of flours works well, but you will need to add xanthan or guar gum no matter what to get the texture you are looking for.
Brown rice makes a great thickener for sauces and gravies. It works quickly and is smooth.
@ CookOnTheFly: Actually, you don't necessarily need xanthan or guar gums to make the texture "real" in gluten-free baking. Sweet rice flour in combination with other gluten-free flours can give a completely believable texture (no one will be able to tell the difference). Another option is to make a slurry out of ground chia seed and hot water, then use that along with other gluten-free flours. Gluten-Free Girl (http://glutenfreegirl.com...) has been writing about this lately and I can testify that it works perfectly.
I don't eat soy any more, but I used to use soy flour as an essential ingredient in vegan pastry to help give baked goods color. Things would come out more golden brown. I would use about one tablespoon per cup of flour.
Brown rice flour is great for gluten-free baking. I use it in conjunction with chickpea flour and water chestnut (or tapioca) flour to make gluten-free pastry, brownies, cakes, etc. It is also great in pancakes.
The soy can be used in yeast breads too but be careful...it has a strong flavor. Maybe half cup to start.