Baking Basics 101 - Non-wheat Flour Part 2

Soy Flour
Soy flour is made from soybeans. This type of flour is one of the best alternatives to wheat flour for people with wheat protein allergies. Common practices before soy flour is usable is to "de-fatten" the flour to prevent spoilage and to heat-treat it to remove the strong flavor. Common usage in wheat bread is below 3% without any noticeable change in dough performance or taste. Beyond the 3%, there will be a noticeable difference in gluten formation and structure. This is due to the lack of elastic properties in soy flour. When used in doughnuts, up to 15% soy flour can be used to reduce oil absorption and improve shelf life. As mentioned earlier, the 3% is not a rock solid rule - chemically leavened items can incorporate higher soy flour than yeast products.

Barley
Barley is the other oldest grain aside from wheat, with records dating to the Middle Ages. In breads, malted grain (with the aid of barley) is used to aid wheat flour in good fermentation for yeast breads. Malt is also used to transform grain mashes into beer or liquor. Barley can come in many forms: hulled (the husk is removed), pearled (removes bran & germ), flakes (flattening the whole seed like rolled oats), and flour (in multiple whole-grain sizes).

Oats
Oats come in many forms: rolled oats, quick oats, steelcut oats, and oat flour. Oat processing has multiple stages: the husk is first removed from the grain, then they are hulled, heat treated to soften the oat berries and to kill the enzymes that cause rancidity in oat berries fats. At this point, the oats can be rolled (flattened between rollers), or cut before being rolled (for quick oats). Steelcut oats are unflattened quick oats, while oat flour is a by-product of any of the earlier processes. Rolled oats are used mainly in cookies, whole-grain bread, strusels, and granola. Oat flour is typically used in chemically leavened products like pancakes, waffles, and muffins. Due to the lack of gluten, oats cannot be used in place of wheat in bread products (only as a compliment).

Millet
Millet is a multitude of unrelated grains put into one name. One of the more popular ones is Sorghum. General characteristic of millet is the small size and high protein content of 16-22%. Millet usually grow in poor conditions (hot, arid, and poor soil) and commonly used as porridge, unleavened bread, or beer. Cooked millet can be used in wheat breads.

Potato Flour
Potato flour is essentially ground dried potatoes. This flour or dehydrated potato flakes can be added to wheat flours in low percentages (around that magic number 3%) to help retain moisture and softness while acting as an extender. Potato flour has more thiamin, riboflavin, and niacin than wheat flour as well as containing 8% protein content (but mostly made of starch). Potato flour is popularly used in Passover cooking where grains are not allowed to be consumed, as well as gluten-free recipes in combination with other flours. An interesting experiment would be to add some sweet potato (kamote) flour into a recipe.

Buckwheat
Buckwheat is not a grain or cereal, but rather a type of dry fruit. Growing well in cold climate and poor soil (would explain buckwheat's connections to Japanese and Russian culture/food), buckwheat's flour form can be used successfully in breads, pancakes, and noodles. The whole grain can also be cooked whole like rice.

Spelt
Spelt wheat is one of the ancestors of modern wheat. Spelt can be prepared like rice and has a mellow/nutty flavor. Spelt protein is a good alternative for wheat allergies and spelt flour can be used as a substitute for wheat flour.

Quinoa
Quinoa is part of a family of plants including beets, chard, and spinach. Primarily South American in origin, quinoa has many tiny seeds that look like a combination of sesame and millet. Quinoa provides high nutrients such as protein, magnesium, iron, and potassium. Usage of quinoa includes healthy wheat breads (either cooked whole or soaked), ground and incorporated in small portions of wheat flour in bread, cookie, and muffin recipes. Since quinoa does not contain gluten, it cannot be used alone in most baking recipes except for waffles, pancakes, or certain cookie recipes where gluten is not important.

Amaranth
Amaranth is an herbaceous plant coming mostly from Central America. Seeds are also rich in nutrients (like other poor-soil plants) with a unique flavor. It can be used similarly to quinoa in healthy breads, and also has no gluten proteins. Also similar to quinoa is the usage, where breads and cakes need a mixture of amaranth flour and wheat flour for the gluten formation.

Tapioca
Tapioca is a starch made from the cassava root, and is colorless, flavorless, and odorless. Common usage of tapioca is a thickening agent or as small pearls for desserts, but can also be turned into a flatbread (like in South America) or as a tortilla (like in Brazilian cuisine). Tapioca can sometimes be the main component of maida flour, but for the most part it is made with wheat flour.

Arrowroot
Arrowroot is a popular thickening agent made from the rootstock of the arrowroot plant. While some view arrowroot solely as a premium thickening agent for sauces (especially Western cuisine and mostly because of its good resistance to acidic properties), arrowroot has also historically been used in papermaking. Starch content is very high at 23%.

For more information on flour
Wikipedia article on Flour
Epicurious article on Flour
Joy of Baking article on Flour