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AFTER NEARLY 30 years of growing popcorn and food-grade corn for several snack food companies, Scott McPheeters of Gothenburg, NE, had a load of food corn rejected in 2002. The load tested positive for StarLink, a genetically modified (GM) trait unapproved for use in food.

“It could have been a false positive,” McPheeters says. Regardless, the grain had to be channeled to the feedlot spot market, garnering him $0.70/bu. less than the contract price and costing him the additional $0.30/bu. quality premium he otherwise would have been paid for his food-grade corn.

McPheeters says almost every farmer he knows has had corn rejected. “They kind of say, ‘Well, ya, I had one rejected,’” McPheeters says. “And of course you don't want to tell anyone because it is like a Scarlet Letter. But the truth is, it does happen.”

Ensuring grain purity and quality is gaining importance on Midwest farms as more growers like McPheeters grow crops outside the commodity realm to a receive a premium for their grain.

Buyers do not want foreign grain mixed in and hold growers to strict quality standards that must be met for the grain to be accepted. “There are some buyers attempting to impose zero contamination standards,” says Dan Ess, extension agricultural engineer at Purdue University. “And when we have farmers who are trying to comprehend how to deal with that, that is why this topic has become important.”

Keeping unapproved grain out of value-added grain shipments is a management challenge that can have a high cost if grain is rejected. Although a grower can follow various strategies to help ensure grain purity, one strategy that can have a direct impact is to thoroughly clean the combine before switching crops.

Where grain hides

All farm equipment requires cleaning, but the combine is especially important because of the volume of grain it holds and the number of areas where grain can get trapped.

“Combines are designed to meet a lot of different needs, but cleanout is not near the top of the design priority list,” Ess says. “It is interesting how many flat surfaces are designed in the grain tank that all seem to want to trap grain.”

Ess along with extension engineer Dirk Maier and graduate research assistant Nathan Fleck recently conducted a study to measure the amount of material that remains in a combine at crop changeover. Their results were published in a bulletin released in April titled “Where grain hides in a combine.”

After studying a variety of combine makes and models, the researchers found that a combine can hold up to 192 lbs. of grain and other material even after the machine is allowed to run empty for several minutes. “It's hard to believe how much material remains in a combine at crop changeover,” Ess says.

Areas that harbored the most grain were the rock trap, header, grain tank and feeder house. Other common hiding spots included the unload auger, tailings and elevators, chopper and cleaning shoe.

Grain contamination occurred even after the initial flush of a new crop had moved through. Trace amounts of old crop were found in the first and second hopper of new grain collected. It wasn't until the third load of the new crop that old grain was no longer detected.

Tolerance standards

If all you grow is commodity corn or soybeans, a few kernels in the combine left from the previous crop may be acceptable. However, if you are growing a crop for any other use, quality standards will dictate how much if any foreign material can be in your sample. Standards can range from 0 to 5% or higher, depending on the buyer.

According to Purdue University's Dirk Maier, a zero-tolerance standard applies to any GM trait that has not received approval from the USDA Animal and Plant Health Inspection Service for commercial release in the United States and the markets of our major buyers. “An example of that would be StarLink from a few years ago and more currently the Syngenta Bt 10 trait that has been found in the export channel to Japan,” Maier explains.

Zero tolerance also applies to GM traits that have not yet been approved in Europe but have been approved in the U.S. and in the markets of our major buyers such as Japan. “This is known as the MarketChoices Corn program,” Maier says. “When it comes to cleanout and segregation of any other traits, that is, GM versus non-GM grain or quality attributes such as white versus yellow corn, the marketplace has established reasonable tolerance levels.”

Growers can go to for more information about grain quality standards. Maier says growers who are able to meet or exceed buyers' expectations with respect to supplying grain quantities of consistent quality will have a competitive advantage.

How to get to zero

Using an initial flush load that fills the grain tank completely can help get rid of grain from the previous crop from your combine. But removing every kernel to meet zero tolerance standards will require a physical cleanout.

Cleaning a combine can take anywhere from 45 minutes for a quick cleanout, up to 48 hours or more if you need to disassemble and clean each part. The quick version involves opening access doors and blowing off each part.

The time and effort required will depend on the quality standards set by your buyer. According to Purdue's Ess, if a stringent protocol is in place, a cleanout would require one person working a full day. “But you know how important a day during harvest season can be,” Ess says. “So what you typically see are multiple workers attacking a machine trying to get it turned around in less than a day.”

Mark Hanna, extension agricultural engineer with Iowa State University, has devised extensive cleanout procedures growers can use to help eliminate grain from not only combines but also planters (see sidebar).

Two rules apply

Many steps are involved in a thorough cleanout. But in general, Hanna says, two basic rules apply.

The first is to use air as opposed to water. Either compressed air or a shop vac is acceptable.

“Some people use water,” Hanna says. “But water can be considerably more hazardous to the health of equipment if sprayed on bearing surfaces or unpainted steel at high pressures.”

The second rule is to work from front to back and top to bottom. “In other words, be systematic about it so that as you are chasing grain around, it is falling lower and you have a better chance of finding it,” Hanna explains.

Start at the front of the combine and clean the header, feeder house and rock trap. Then move to the top of the combine and clean the grain tank, unloading auger, and sump, eventually working your way down to the cleaning shoe and out the back of the machine.

The rock trap, one of the areas holding the most grain, is dirty and difficult to clean. But once you get inside, it can be cleaned out fairly rapidly, Hanna says. “It is sort of the low-hanging fruit in terms of cleanout out the machine,” he says.

Other areas, such as the grain tank, unloading auger or header, can also harbor large amounts of grain but will take longer to clean. Compressed air will work for most of those areas. But normally a shop vac is required for the grain tank to get grain out of the sump area.

One area often overlooked is the moisture sensor used for yield monitoring. Located in the clean grain stream, the sensor will not unload completely without help. For example, one of the combines used in the Purdue study contained more than half a pound of clean grain in the moisture sensor when emptied.

Hanna also cautions against turning on the combine while doors and shields are off due to the risk of getting caught in moving parts.“It is tempting once you get the combine opened to start her up and blow things out that way,” he says. “But pretty soon you start to consider looking inside the machine, and all it takes is a slip or fall and it becomes a real safety issue. So the game here is to clean things out as best as possible with compressed air or vacuum air rather than turning the machine on and attempting to blow the things out.”

Finally, Hanna says once you complete the job, document what cleanout procedures you followed, along with signatures and dates. The documentation can be used to prove you followed protocol in case grain purity is questioned.

Support from manufacturers

Because of the importance of combine cleanout, and the inherit difficulty involved, machinery companies are helping growers with the task. Deere, for example, trademarked a training program in 2003 called the Grain Quality Delivery System to help growers of specialty grains achieve the required level of quality, protein, moisture or cleanliness.

Richard Bull, project manager of John Deere combine harvesting and grain management, started the program in 1997 after discovering how few growers knew how to harvest specialty grains. “I used to go to dealerships all over the United States, and I was lucky if I got 2% of growers to do everything they were supposed to do,” Bull says.

Under Bull's program, certified John Deere dealers instruct growers on how to adjust and clean their combine to harvest barley, food corn, popcorn, seed sorghum, seed wheat, rice and edible beans. “We just finished up the book for edible beans and we are now working on one for grass seed at the request of the branches,” Bull says.

CNH introduced a similar grain-quality program in 1983 for its customers, according to Terry Snack, Case IH combine applications manager. “We have a lot of customers who raise specialty crops or identity-preserved grain to get that extra $0.25 or $0.30/bu. premium,” Snack says. “And they have to sanitize and clean their equipment as they go from one variety of seed beans to another variety or from white food grain corn to yellow or commercial corn.”

Under the program, Certified Case IH dealers trained in combine adjustment and cleanout conduct grower meetings to train customers how to achieve grain-quality standards. “We work with grain processors to make sure our combines perform at their peak,” Snack says.

Designated equipment

On the downside, thoroughly cleaning a combine between crops takes time, money and labor that some growers may not be able to afford. And it ties up equipment at peak harvesting time.

What's more, unless growers follow the most rigorous cleanout procedures, grain contamination can still occur, according to Purdue University's Dan Ess. “There is going to be some contamination unless you follow these absolutely strenuous protocols that really do have a lot of consequences and costs associated with them,” Ess says. “So sometimes it looks like we outline cleanout protocols just to say, this is probably not what you will be able to afford to do.”

As an alternative to in-season cleanouts, Ess advises growers to have a separate line of equipment that is dedicated to certain types of crops.

“If you look at the used combine market, there are a lot of bargains out there,” Ess says. “And rather than taking 24 or 48 hours out of your peak harvest time to tear down machines and clean them out, you may be able to budget for an older machine you can just have doing one type of crop.”

Food-grade corn grower Scott McPheeters agrees that the whole process is management and capital intensive. “It is probably not for the faint of heart,” he says.

As a result, he says, growers need to ensure there is a high enough premium in the crops they sell to cover those additional costs. “In other words, if you are going to go to all of that work but can't market them as GMO-free or supply someone who values that, you have just jumped through a lot of hoops that are costly.”


Combines are being redesigned to aid in grain cleanout between crops to meet grain purity and quality standards. “If you go back 28 years ago to a 1400 series combine, it may have taken a grower three to four hours to sanitize his machine,” says Terry Snack, combine applications manger for CNH. “Today he can do it in an hour or two.”

According to Snack, at least 10% of the company's design focus now is on how to make Case IH combines easier to sanitize from one crop to another.

Richard Bull, project manager of John Deere combine harvesting and grain management, echoes that statement. “Grain quality and purity issues have a very big influence on design,” Bull says. “And we will continue to make it easier and quicker to clean our combines because we realize it is going to become even more important as years go by.”

Following are changes that have been made to date, which come standard on new models:

Case IH

  • Contoured the design of the grain tank to make it easier for grain to pass through.

  • Eliminated flat spots and ledges where grain can get trapped.

  • Added filler plates in the grain tank.

  • Added cleanout ports to the clean grain auger, tailings auger, grain tank cross augers, and grain pan area to ease cleanout.

John Deere

  • Added doors to make it easier to access and clean conveyer cross augers.

  • Made it easier to remove covers over grain tank cross augers by replacing bolts with pins that can be pulled out and removed without the use of tools.

  • Improved access to the vertical unloading augers for easier cleanout through slots in the casting.

  • Switched from metal to molded polyurethane side and rear panels so grain slips off the surface instead of becoming trapped in edges, ribbing and support braces.

  • Improved access to threshing and shoe areas to ease cleanout.

  • Changed engine design to divert airflow over the engine to keep it cool and clean.

  • Added stone trap to prevent large objects from entering grain sample.

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