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Seed Cleaning Tools and Techniques

To Rob and all other seed cleaners:

I've had a lot of experience with seed cleaning.  Here's a summary of tools
and techniques that I've used.

GENERAL TECHNIQUES

Start off by using screens to remove the fines (mold spores, dirt, etc.) and
coarse chaff, then go to the specialized cleaning techniques.  Since I
usually work with mint family plants, these techniques are most useful for
round to oblong seeds.

SEED SCREENS

I started with a 16 x 16 screen from window screen, and a 40 x 40 screen
from the brass hardware cloth supplied for use as a water filter at hardware
stores.  My frames were made from #1 1 x 4 pine cut to make a 12 x 12"
frame.  I ripped off a 3/4" piece off the sides to make the trim that held
the screen on the rest of the frame.  

Next, I invested in some inexpensive special size screens from Burrows
Equipment Company.  I got sizes (10 x 10, 14 x 14, 24 x 24, 32 x 32) that
were not available from common sources.  Made with stackable wood rims, they
cost $11 apiece in 1979.  

Later, I made 14 x 18, 18 x 18, 36 x 36, 42 x 42, 48 x 48, and 60 x 60
screens from samples given to me from hardware cloth used in the factory for
dust control equipment.  

Gilson supplies lab screens, but these are expensive ($25 for 3" to $80 for
12" apiece), depending on the diameter, depth, and construction (brass or
stainless steel).   These are the screens one most often sees in academic or
industrial labs.  

AIR SEPARATOR TOWER

Burrows also had a tower with air blown upwards through a sample with
carefully controled air flow.  This would allow lighter chaff to be blown
out first, leaving the usually heavier, viable seed at the bottom.  By
slowly increasing the air flow, more of the chaff and lighter, immature seed
could be removed.  

Working such a tower is an art.  One needs to know how much material to load
into the tower, what air flow to use, and how many tower sections to add to
get an effective separation.  It should be possible for a gifted handy man
to make one starting with an old vacuum cleaner.  The process is similar to
distillation of organic compounds using a fractionation column.

TRAYS AND BOWLS

Trays can be used to separate seed from chaff.  Much seed is denser and
usually round or oblong.  By taking a beer flat or similarly sized plastic
tray and laying down a half-inch wide row at one end and shaking the tray
with a regular motion at just the right angle, one can induce the more
desirable seed to separate first and roll to the bottom.  The intermediate
material can be sent back to the top by lightly blowing on it for a second
or third chance.  The art is in picking the right angle, motion, and load
for the seed variety.

A variation of this is swirling in a bowl.  With the right amount of seed,
very often the best material will collect in the center, and the chaff on
the outside.  It is important not to overload the bowl.  A deep stainless
steel bowl (3" deep, 4" wide) works best for me.

If you want to blow harder, you can remove the chaff entirely.  This is a
messy but highly effective process.  One word of caution: you can blow some
of the chaff into your eyes.  I once scratched my cornea pretty good doing
this, so wear protective glasses.

ELECTROSTATIC GUN

Sometimes electrostatic forces will interfere with seed cleaning, especially
with small seed.  The way to remove this is to use an electrostatic field
generator.  I have a Zerostat 3, made in England for Discwasher.  It
produces a charge by squeezing a piezioelectric crystal.  One charge is
produced by squeezing, and the opposite by releasing the trigger.  This
should discharge the particles, allowing them to flow freely.  I got my gun
at a stereo center or an electronics supply store.  It is designed to remove
dust from CDs and LPs. 

GERMINATION TEST PAPER

Burrows also supplied Kimpak Germination Paper in boxes of 100 sheets (about
$18/box in1979) in various sizes.  The paper is sterile, has no injurious
chemicals, and holds 16 times its weight of water, so it should be ideal for
Deno's method.  It works for both small and large seeds.

ADDRESSES

Burrows was with Soiltest, Inc., but was either spun off or disbanded.

Gilson Company, Inc.
800-444-1508
P. O. Box 677
Worthington, OH  43085-0677

National Seed Storage Lab in Fort Collins, CO:

http://checkers.nssl.colostate.edu/people/people.htm

A list of scientists who specia;ize in seed research.

MidWest Seed Germiation Service

http://www.brookings.com/mwss/germ.htm

A company that does seed testing.  They may be able to provide leads for
sources.

Hope this helps,

Rich Dufresne
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