Raw Cereal Grain
An extensive array of raw grain like corn, rice, wheat, oats, barley, quinoa, millet, sorghum, buckwheat and rye can be found in virtually any store that sells bulk groceries. All can all be used to make your beer more interesting. Rye and buckwheat in particular have a fairly strong flavor and will stand up to darker brews. Others are useful to lighten body while adding fermentables, contributing a minor flavor profile, and/or adding some mouthfeel, silkiness and texture at the same time.
The key to using them, though, starts with a process called gelatinization, essentially cooking the raw grain with water to swell and unfold the starch, transforming it into a fermentable product.
The method entails cooking the grain separately and then adding it to the main, malted grain mash. Essentially, you will be making a batch of thin hot cereal. Mill the grain as you would your barley malt and mix with enough water to make a loose porridge, then cook until soft, usually 20 minutes or more. Bear in mind that the cereal will absorb a lot of water so be mindful of scorching.
When the cooking step is finished, cut off the heat and mix in enough cool water to bring it to roughly your mash temperature. It will take a bit of shrewd coordination, as there will be malted grain in the mash tun and cereal in a separate kettle, but as with most homebrewing experiments, a little planning and confidence goes a long way (breweries that use adjunct grain or cereal have a separate cooker for this very purpose).
The malted grains in the mash have more than enough enzymatic power to convert the raw, gelatinized grain to fermentable wort. Keep the raw grain portion to 30 percent or less of the total grain bill by weight. Stir the mash now and then to keep the enzymes in contact with the starch. It never hurts to add a pound of inert rice hulls to the mash to aid in lautering, since raw grain contains no husk.
It is useful to know that some grains have a low gelatinization temperature and can be used without cooking. Wheat is one, and this is why raw wheat is used in witbier to full effect and without any adverse consequences. Most need cooking, though, so to be safe when using any of the others, do the gelatinization step.
Classic American pilsner uses about 25 to 30 percent corn grits, and was the first lager made by Central European immigrants. Buckwheat is outstanding in porter, stout and brown ale. Brown rice is a nice, nutty addition to lighter ales. Even multi-grain recipes can be formulated, provided you have enough base malt to complete the conversion of the starches. Rule of thumb would be to start with about 20 percent adjunct and go from there. Oats and rye are very popular grains for their mouthfeel and flavor contribution, and are usually used in flaked form.