The purpose of this thread is to help define the properties of many gluten-free flours. That is, the attributes which make a particular flour good or bad for certain types of recipes. Some of my comments are only my opinion, and I'm sure you'll be able to pick them out. My main focus has been whole grain flours, for more hardy breads. Also, there are some flours (mostly starches) which I can't eat, so I hope others will be able to fill in the gaps. If your experience differs, please post about it!
Amaranth Flour
Adds wonderful aroma and flavor, and helps with browning. Retains considerable moisture compared to most other flours, thus best used in relatively small amounts. I find it only takes one or two teaspoons per cup of total flour to make a difference.
Buckwheat Flour, whiteThis flour seems to work ok in a variety of things, though I haven't noticed anything outstanding. Sorta similar to rice flour, but not grainy. Bland compared to the brown buckwheat flour, which I like much better.
Buckwheat Flour, brown***Good in sweetbreads, muffins, brownies, and the like. Stronger flavor than most other flours. Goes with cinnamon and other spices, raisins, apples, etc. Good texture, and not too moist. Accepts oil, though not quite as much as most bean flours.
Fava Bean Flour***This one can be used alone for pie crusts, crackers, and the like. Able to take up oil, which results in the dough becoming stretchy (not elastic). This can help breads to rise, which I think is why bean flours are included in many blends. Helps with browning too.
Garbanzo Bean Flour***Similar to Fava, but I generally don't use it. Haven't tried it much in breads yet however.
Garbanzo & Fava Flour***Somewhere between the two types. The one I've used smells much nicer than either one alone.
Millet Flour*Good for most things, but seems to dry out on the surface more than others. The particular blend (or other ingredients) may compensate however. Otherwise it's a lot like sorghum flour.
Quinoa FlourBitter!
Rice Flour, brownGritty by comparison to other types, though I hadn't realized how much until trying millet and sorghum. I no longer use rice flours.
Rice Flour, whiteNot much different than the brown, except for the color, and more bland of course.
Rice Flour, Sweet White**Helps the rising/texture, but can easily add gumminess. I never found the right blend to solve that entirely, without introducing other unfavorable qualities.
Sorghum Flour*Good for most things, and doesn't seem to have the surface drying characteristic of millet flour.
Soy Flour, full-fatAdds moisture and soft texture. Makes things brown easily. Usually best in small amounts, like 1/5 or less of the total.
Sweet Potato Flour**Though not actually a starch, it's good for what starches are generally used for, and doesn't make the results gummy or brittle. Good for thickening too. Made from the white variety of sweet potatoes, so it's white like a starch too.
Tapioca Flour**Lends a weird texture - a peculiar combination of both gummy and brittle.
Teff Flour, ivory**Adds wonderful aroma and flavor. Helps a tad bit with browning. Good in most things I've tried with it.
Teff Flour, brown**Has a stronger aroma and flavor than the ivory teff. Sorta reminds me of (and goes well with) chocolate, coffee, and the like. Good for brownies, muffins, basically anything chocolate, spice cake, etc.
* Does not accept oil well.
** Can accept some oil.
*** Accepts oil well.
As of this post, I believe it is the protein content which makes the dough stretchy when oil is added. However, oil interferes with the binders, so getting the right ratio of ingredients can take trial and error. The amount of oil used will also vary depending on what you're making, and personal preference. In my experiments, I found I could add maybe a tablespoon or two of oil for each half cup of bean flour. But even if the proportion of bean flour in the recipe is significantly high, it may not work well to maximize the stretchiness. Again, oil defeats the binders, and the stretchy characteristic disappears as the dough bakes. From my experience, the more oil, the more crumbly the texture.
The flours which don't accept much oil tend to just lose cohesion. The dough is oily, and won't work so well for things which need to rise.
Consider how pie crust works: The oil content defeats the binders, making for a crumbly texture. Since gluten-free flours don't have much binding properties on their own, far less oil is required (compared to wheat flour) to get a crumbly crust.
A note about bean flours:
Although the taste of these flours is generally more prominent than other flours, it should not be foul. Adding ground ginger to the recipe seems to neutralize some of the characteristic taste. Freshness is important, and I found that stone ground bean flours are simply rancid, right from the get-go.
In general, I've found buckwheat, millet, sorghum, and teff to be more interchangeable than the others listed. They do taste different, but swapping one for another usually doesn't ruin the results. Unless otherwise noted, I haven't found it necessary to use specific proportions of most of the flours listed. What does make a big difference however, is the amount of liquid added to the dough. I also think the optimal softness of the dough is dependent upon the pan being used, oven time/temp, and probably climate and humidity.
The type and amount of binders used is also an important factor. But typically, one teaspoon per cup of flour is usually a good starting point.
