Specialty malts fall into a few basic categories defined by the method of production. Higher kilned malts generally include those types that have more color and flavor than pale malts and that are produced using the same type of malt kiln as the “standard” pale malts. Munich, biscuit, amber and Vienna malts are examples of types that are made in the kiln.
Crystal or caramel malts are stewed before drying, although not all maltsters use the term “crystal” and “caramel” in the same fashion. Sometimes the terms are interchangeable and the final cure phase may occur in the kiln or in a roasting drum. The process of stewing is similar to mashing, but the mash occurs within the malt kernel. Stewing is accomplished by heating green malt, that is, malt that has completed germination but is not yet dry, to between 140 and 175 °F (60 and 79 °C) in a closed vessel preventing the escape of moisture. Stewing converts starch into sugar and also increases the amino acid content by proteolysis.
After the stewing phase is complete the malt is kilned, where the final temperature used in kilning — often termed the cure temperature — and cure time is altered depending on the degree of color development desired. Crystal malts are often made in roasting drums because the stewing and kilning process is easier to control. An older method, rarely used today, was to begin with kilned malt and rehydrate the grain to achieve a moisture content of about 45%. This was followed by stewing and kilning to produce crystal malts.
Roasted specialty grains include materials like chocolate, brown and roasted malt and roasted barley. These ingredients get their intense colors and flavors by using final cure temperatures up to 400 °F (200 °C) for times up to 90 minutes. Roasting drums are always used for these products and the roasting process is quickly terminated by using water sprays to “quench” the roasted materials before the roaster is emptied. One practical concern when producing highly roasted materials is avoiding fires.
Start out with high-kilned types, like those produced on a drying kiln. A convection oven is a great tool for making specialty malts because one of the key features of a commercial malt kiln is forced air. Without forced air you will have temperature gradients throughout the malt and will get inconsistent results from kernel to kernel. In addition to a convection oven, you will also need some sort of drying tray that you can load the malt into and place in the oven. You can make your own drying tray using a box frame and stainless steel screen mesh. Do not use any material that could be a fire hazard for the frame, however.
Crystal malts would be a natural next step to try. Adjusting the moisture content of dry malt can easily be estimated by simply adding a known weight of water to the malt you wish to rehydrate. The stewing process could be carried out in a covered stock pot in your oven. After the malt is stewed you can turn it out on your drying rack and begin the kilning process in your convection oven. Make sure you read up on kilning methods; the kilning temperature used to dry malt is lower than the cure temperature and maltsters often use a temperature profile to achieve even drying with minimal color-pick before the final cure temperature is met with the goal of producing color and flavor. As far as roasted grains are concerned, I would suggest buying those unless you have a small coffee roaster.