Saturday, May 17, 2008

Cleaning up

(Here's another excellent article by Anthony, this time on cleaning seed. Enjoy and please reply if you have any experiences in this area - Josh)

A grower contemplating growing grains, dry pulses, or any other seed crop, must grapple with the task of cleaning and sizing their harvest.

Well-cleaned beans or grain sell better, and earn a higher price. Under-sized, over-sized and split beans detract from appearance and cooking quality. Chaff and other debris in grain can take a lot of the customer’s time if left in the product, discouraging them from buying from you again. Restaurants are especially sensitive to preparation time issues. For the organic grower, weed seeds in grain are pretty much a given, and need to be removed.

Seed cleaning can be done by hand, and is easily mechanized. For larger operations, the work is typically done under contract by a seed cleaning company. Where a farm has a diverse variety selection in small quantities or organic seed that must be kept separate, on-farm seed cleaning capacity is very helpful. The machines can be a good investment for a farm, relieving a bottleneck to diversification.

I am covering what we have learned about the task, and will be interested in the experiences of others.

At the most basic level, seed can be winnowed outdoors on windy day. My experience is that the wind magically fades as soon as I am ready to winnow. A refinement uses two box fans joined together so they blow in the same direction, one through the other. The beans or grains are poured in front of the fans to blow away the chaff and other light material. The use of two fans produces a strong wind that can be trimmed to just the right level by adjusting the speed of each fan. Screening is done after winnowing. Hand-screens work well, but can be slow. We have a small fleet of homemade screens from our first few years of bean and grain production. For a small CSA, this basic equipment is sufficient, especially for beans and corn.

These components are integrated into the fanning mill. These machines have been around for nearly two centuries, perhaps longer. They use a fan and screens to clean the grain. The earliest employed a hand crank. At one time, there were many brands of fanning mills, and they come in a range of sizes.

The Clipper Office Tester ( ) is a compact fanning mill well suited to a small farm. The machine has a small footprint, approximately 16” x 25”, and weighs about 50 pounds. The screens are easy to store. It is light enough to move outside when cleaning dusty material. The office tester does a very good job, saving a lot of time and producing a very clean batch of grain or seed.

The design of the machine is simple. It accommodates two screens; one on an eccentric shaker for scalping and the other for sifts the seed as the roll down the inclined screen. The seed passes through the scalping screen, removing the large material, and then over the sifting screen, which separates out the small debris. The seed then falls past an adjustable blower which removes very light trash such as corn silk and chaff. The machine takes but a few minutes to clean when the job is done.

The screens can be configured to size seed as well as clean it, and a single sifting screen can be used with large seeds, such as favas, that don’t need scalping. The screens come in 175 different sizes, shapes and opening types. For most seed cleaning we use a round holed screen for scalping, and an oval hole for cleaning. We can clean seeds from mustard to cranberry beans, and all types of grain. We then select a pair of screens that will pull off the over-sized and under-sized beans.

We have modified the Office Tester by attaching it to a rolling Rubber Maid cart (flat topped), the cart and base of the machine were cut to accept a chute. A 35-gallon sits on the bottom shelf below the chute. Takes up a bit more room, but it is much more efficient. I will add that cleaning seeds outdoors also saves a lot clean-up time.

The fanning mill has its limitations. Vetch seed will pass through the same screens as wheat or barley, and is tough to remove. Mustard seeds in oats provide a similar challenge. Small clods of soil will also stay with the grain. A spiral separator is used for separating objects of similar sizes with different shapes; chicklets from gumballs, nuts from washers, and vetch seed from grain. It has no moving parts, and no electricity is needed. The design is very elegant. Go to for a picture of a spiral separator. May be in our future.

b. lucy made reference to a gravity table. These separate out seed based on density and shape. I leave the Lucy’s or some else to talk about this technology.


Anonymous said...

Great blog. I'm an organic market farmer in SW Oregon and our intern has convinced us to put in 600 quinoa plants. I don't have any experience growing grains. I know greens well, but grains. Any resources you can lead me to?

Michelle Ajamian said...

i'd like to know more about the seed cleaner--esp how many lbs per hour does it clean?

Sara, Helge and Thomas said...

hi! I don't know much about grain, but I am interested in buying buckwheat hulls for pillow production. I live in Norway, and I have found a producer of buckwheat hull, but he can not clean them to the appropriate standard. So, I'm wondering if there is anywhere I can buy a machine for small scale cleaning of the husks. Can I use a machine design to clean grains?

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Shagbark Seed & Mill Co. said...

Hi. My partners and I are putting together a regional scale bean, grain, oilseed, and nut processing facility in Southeastern Ohio. (can't figure out how to insert a live link here, so copy, paste, and check us out). I need to find a small commercial scale gravity table, particularly for after running our spelt through our de-huller and seed-cleaner. Some of the seeds that still have hulls on them but are smaller than standard, come through the cleaner along with the finished, naked seeds. I am told that a gravity cleaner would help. Does anyone know where I might find a used gravity table for sale?