Screening is a way to clean corn of the parts that make it difficult to burn in your corn stove. Some stoves on the market claim to be able to burn anything, and perhaps, to a limited degree this is true. But your stove will run best if it is burning strictly corn kernels with no fines, cracked kernels or other material that will impede the air flow from the combustion fan. Also, many corn screeners remove oversize objects like corn stalks, rocks or cob that can clog feed augers.
Keep in mind that corn is unique amongst grains in that it tends to crumble into fine pieces the more it is handled. Thus, it is essentially impossible to remove all the fines by multiple screenings.
This page presents commercial offerings, whereas other pages present DIY, Home_build_corn_screeners
Outdoor Use Cleaners
Some corn cleaners scatter a great amount of dust, or use non-contained fanning systems. These types of cleaners should only be used outdoors.
A very simple way to clean grain is to use a Winnower, which uses wind blowing across the grain to remove foreign material. A winnower uses a fan, either powered or hand crank, that is blown through the grain as it drops from a height.
A more complex unit is called a Fanning Mill. Typically a Fanning Mill is built to perform a three part process. First, a coarse screen that allows corn kernels to fall through. Larger peices, such as cob and stalk float over this screen and fall into the waste bucket. Second, a fine screen, that kernels float over the top and broken kernels and smaller bits fall through and into the waste. And finally, a wind burst that removes dust and chaff from the kernels.
Here is a photo of the Clipper M2B fanning mill which is available for ~$2850.
This cleaner is almost the exact layout of the diagram above. It has a hopper at the top that the corn can be augered or bucketed into. The corn flows down over the screens inside. An optional "Sacking Auger" allows grain to be bagged for storage.
Indoor Use Cleaners
Other forms of cleaners are available on the market and better suited to indoor operation. These cleaners usually rely on a sealed system of dust containment. Usually, but not always, based on a shop-vac to contain the explosive corn dust.
This unit could be placed next to a basement corn burner. It utilizes a shopvac for the airflow needed to do dust and chaff collection. Primarily though it depends on gravity. The corn falls through several different screens that remove the over, and under, sized material from the kernels of corn.
The real advantage to these units is their small footprint. They take up very little floor space. They do pretty well at removing foreign material. Also they do well at containment of dust, so they can be used indoors without getting too much dust in the living space.
However, these cleaners only perform as cleaners. They provide no means of moving corn as in vacuum based mover/cleaners http://forum.iburncorn.com/wiki/index.php/Vacuum_based_systems.
The small size of these cleaners mean they can only clean a small volume of corn, slowly fed. Cleaning 5-10 gallons of corn a day would be within the capabilities of this cleaner. For larger volumes than this, you will want to look at a bigger cleaner. It is likely most of the owner complaints come from larger quantity burners.
Another option in the category of small cleaners, The Fasturf, shown perched on 2 buckets, is also designed for cleaning small quantities of corn indoors. It is an interesting design because where most cleaners use a blower fan to remove dust, this unit uses a shop vac to suck the dust from the screens.