Adding Value with Seed Cleaning
Fact Sheet | Adding Value with Seed Cleaning
INTRODUCTION
No one wants to eat breakfast and find an extra ‘bite’ of a stone in their oatmeal. While some crops, like corn, are generally harvested with less foreign material, and do not require dehulling, most grain lots will include foreign materials that can be helpful to remove. Seed cleaning is the term for practices that remove debris, dirt, unwanted plant material, weed seed, and other contaminants from a harvested crop. Seed cleaning uses differences in physical characteristics between desirable seed and undesirable material to make separations. Farmers clean their seeds for a variety of reasons, using many different methods.
WHY FARMERS CLEAN THEIR GRAIN
Cleaning harvested grain in order to remove plant material and other undesirable particles can help a farmer in several ways:
Add Value
Grain that will be sold as ‘food-grade’ commands a higher price than ‘feed-grade’ or ‘commodity’ grain. Only grain that is extremely clean can be sold into the food-grade market. The more foreign material there is in a grain lot, the more expensive it will be to clean. Cleaning or dehulling grains on the farm, rather than sending them to a mill or custom dehuller, gives the farmer a higher return.
Increase Storage Quality
Cleaner grain is higher quality grain, because foreign material can cause problems. Weed seeds in grain can leave an odor and affect storage. Weed seeds generally contain more moisture than the crop, and any heavier material, like moist weed seeds, tends to collect in the center of a storage bin. This can restrict airflow through the bin, hampering drying, and potentially spoil the grain.
Marketing
Clean grain makes a good impression that can help maintain positive relationships with buyers and consumers. While there is a commodity market for organic grain, buyers are attracted to farmers who produce consistently high quality grain. The higher quality in a grain lot, the higher value purposes it can be used for, and the higher the price it can command. Cleaning allows farmers to reach the higher test weights that are preferred by buyers, especially in the valuable food-grade market. It is important for farmers to clearly understand the grain quality specifications of their contracted buyer, and to maintain consistent communication with their buyer if a crop will need more cleaning or not meet specifications.
The higher quality and germination rate achieved by seed cleaning can also allow a farmer to sell their grain as certified seed, fetching a higher price. Farmers who send dirty grain can face penalties, or ‘dockage,’ from a buyer, since the buyer will either have to clean the grain or use it for a less valuable purpose.
Reduce Costs
Cleaning and dehulling grains reduces storage space, shipping volume, packing, and the cost of transportation. Farmers who clean their own seed can plant it and save money compared to purchasing seed. The ability to save and plant their own seed also allows a farmer to preserve and grow less common varieties that may be preferred by a buyer or consumers. Additionally, some of the by-products of cleaning/dehulling, such as hulls, can be sold for animal feed or bedding.
SEED CLEANING FUNDAMENTALS
Seed cleaning is the process of separating desirable seed from unwanted material by leveraging differences in physical characteristics. These characteristics include size, shape, density, surface texture, terminal velocity, electrical conductivity, color, and resilience. The cleaning process often involves multiple steps to achieve the desired purity and quality.
Size
Separation by particle size is the most popular way and often the first step in cleaning. Particles of different sizes can be separated by:
• Scalping - a screen allows the desired seed to fall through while catching larger particles/weed seeds.
• Sifting - a screen catches the grain but allows smaller particles to pass through.
Weight
Differences in particle weight can be used to separate seeds, often with an air column or aspirator. These systems pass a stream of air over the seed, blowing out lighter, often unviable seeds while allowing heavier, viable seeds to remain.
Surface Texture
Surface texture can also be used to differentiate seeds. When grain is placed on an angled, vibrating, roughened surface, round seeds roll to the bottom while flat seeds are caught on the textured surface.
Color
Color sorting is a highly accurate method that uses an optical sorting machine. The machine ‘sees’ and removes foreign material based on color differences between the grain and unwanted material.
Shape
Seeds can also be separated by shape using a spiral separator. This works because round seeds roll faster than flat or irregularly shaped seeds, allowing for effective sorting.
EQUIPMENT FOR SEED CLEANING
Seed cleaning is a process that involves many steps from the field to the consumer’s plate. Combines ‘combine’ the jobs of harvest, threshing, and winnowing. They do a great job of initial seed cleaning. A combine built within the last 20-30 years should get grain 95% clean. Setting up the combine correctly to clean the specific crop (for example corn versus soybean) is important, and every farmer has different preferences and practices.
EXAMPLE
Each farmer follows unique methods and approaches for combining. Whereas some farmers want their combine to clean the grain as much as possible, others adjust their combine to capture weed seeds with the grain in order to remove weed seeds from the field. These weed seeds will need to be removed in a later cleaning operation.
Here are the most common operations and machines you’ll see used to clean grain:
Threshing
Threshing is the process of crushing seed heads into what is called chaff. The dry seed heads attached to the plants are rubbed or crushed to release the seed and break down the plant material into small pieces.
Winnowing
Winnowing is the process of separating seeds from the chaff by blowing air. Fanning mills, air seed cleaners, aspirators, and pneumatic separators all use air that is forced by fans to separate lighter objects from grain. Fanning mills and other air cleaners are a cheap and simple way for many farmers to start cleaning their grain. Fanning mills can often get a grain like wheat to 98% purity.
Rotary Cleaner
Rotary Cleaner is a preliminary cleaner that is commonly used to remove weed seeds. They are often portable. When grain is unloaded from carts into the bin, farmers will often run the grain from the cart through the rotary cleaner into the bin to remove weed seeds before storage and/or drying.
A rotary grain cleaner
Screens and Sieves
Screens and sieves eliminate pieces larger than seeds, such as stems and leaves, or pieces smaller than seeds, such as dust and chaff. The most common seed cleaning equipment that utilizes screens is manufactured by the Crippen Company. These machines hold one or several interchangeable screens. It is wise for farmers to acquire many different kinds of screens so that they can remove various types of foreign material.
A Crippen, M-5472 grain cleaner
Dehulling
Dehulling is the process of separating the seed hull from the grain. It is necessary for certain grains and specific buyers. For example, maltsters require dehulled barley. Most dehullers can process different crops, but their speed, yield, and efficiency vary between machines. To increase versatility, dehullers may require modifications and additional parts customized for specific grains, which can further add to labor costs and cash outlays.
Gravity Table
A gravity table separates grain from objects that are either heavier or lighter through vibration and forced air. This piece of equipment is very useful to farmers because it can clean grain like wheat to 99.9% purity. However, used gravity tables are difficult to find, and new ones can be expensive.
Optical Sorter (Color Sorter)
An optical sorter, also known as a color sorter, is an electronic machine that sorts materials according to their color. Because they are expensive, they are best suited for larger operations. Although their price puts them beyond the budget of most farmers, prices are gradually decreasing as they become more common. Optical sorters are particularly helpful for hard-to-remove debris that cannot be removed by magnets and is not easily screened, like certain weed seeds and rodent feces.
Polishers
Polishers are used to clean and brighten the surface of beans, peas, and other grains to make them more attractive to consumers. Some polishers agitate the grain with a compound like sawdust or bran in either a wet or dry process. Other polishers use a revolving brush to scour the grain against a rubber or screen surface.
Handling Equipment
Handling equipment, like augers, conveyors, and vacuums, is essential for moving grain through the different cleaning processes and storage locations. This includes transferring grain from combine to grain cart, from grain cart to cleaners, from cleaners to bins, and from bins to trucks.
Dust Elimination
Dust elimination equipment is often helpful because the cleaning process creates dust, which can cause safety hazards such as explosions, and health hazards airborne particulates. Any time grain is being moved, dust is generated. A dust elimination system can significantly improve the comfort, health, safety, and efficiency of personnel in a seed cleaning plant.
Seed Cleaning Tips for Organic Farmers
Before beginning a cleaning operation, take time to choose the right equipment and settings—this allows the machine to do the work for you and saves time.
Getting seed to 90% purity is the easy part; cleaning the remaining 10% is
the hardest.Be persistent and prepared to repeat and rerun lots, as seed cleaning is rarely a “one pass and done” process.
FAST FINANCIALS
Cleaning, dehulling, and other post-harvest operations should be separated for planning and bookkeeping purposes, so that it is possible to determine how much value is added by each process, and whether it is profitable to invest in and maintain each operation. Here are some considerations:
Time
If farmers spend too much time cleaning, they won’t make money. Generally speaking, don’t obsess about perfection in cleaning seed. It usually doesn’t pay a farmer to clean their grain any more than 98-99% purity, after that the cost goes up dramatically.
The Cost of Outsourcing
It often costs $1-2 per bushel to get seed cleaned off the farm. Farmers can keep those dollars on the farm if they have equipment to do it themselves.
Type of Crops
What crops are farmers choosing to clean? Cleaning crops with higher premiums or value can lead to better returns.
Labor
Labor costs tend to be 1/3 of the cost of cleaning. Machines like color sorters require a skilled operator. Training an operator isn’t quick. While the principles are simple, choosing the right sieve size and other settings to match the materials is an art. It is very helpful to retain employees because they will develop a deep knowledge.
Cost of Equipment
Machines that can accommodate multiple crops enable the cost of the investment to be spread over more crops. Also, don’t forget power - electricity is a close second after labor for highest expenses in running a seed cleaning business.
Cost of Transportation
Trucking beyond a 300-mile radius is uneconomical for grain in most markets. Transportation costs per mile and per bushel increase with smaller loads, so farmers can reduce transportation costs by selling larger lots. And because most carriers charge by volume rather than by weight, hulled grains are more expensive to transport than the dehulled grains.
Cost of Certification
Organic farmers who are cleaning or dehulling grains for other organic farmers need to get certified as an organic handler. And for those selling certified seed, beware that germination testing can get expensive.
Premiums
Seed cleaning allows farmers to vertically integrate their production through direct-sales to consumers. Several organic grain farms have their own label with retail-sized packages of their grains, and sell to grocery stores or direct-to-consumer through their own online store.
Research reported in this publication was supported by The Organic Center and the Foundation for Food & Agriculture Research under award number Grant ID: TOCFFAR-EXT-002. The content of this publication is solely the responsibility of the authors and does not necessarily represent the official views of The Organic Center and the Foundation for Food & Agriculture Research.