More Bean Basics.
August 12, 2004
Grain combines are frequently used for harvesting edible beans but growers with large acreages often use special bean combines. They usually have two cylinders specifically designed for bean threshing and special separating and cleaning units. These special combines do not contain augers and usually move beans with conveyor belts or bucket elevators.
Conventional combines with rasp bar cylinders work well for beans and the new type rotaries are very good. Rotaries tend to cause less impact on the seed and less seed crackage. Tests have shown significantly lower cracked and broken beans as compared to conventional combines.
Rotary combines should be equipped with specialty dry bean rotors and the appropriate threshing bar configuration to provide optimum threshing and separation.
Combining should begin when beans reach 18% moisture content. Combine cylinders should be run only fast enough to do a complete threshing job. Some machines may need special speed reducers to obtain proper speed. High cylinder speeds and allowing the seed to become too dry substantially increase seed cracking and splitting. When beans are at 18% moisture, the cylinder should be operating at a speed as recommended in the operators manual. It is difficult to give one cylinder speed, as diameters of cylinders and rotors vary from 17 inches up to 30 inches in diameter. It is usually best to set cylinder speed as slow as possible and check to be sure that pods are threshed to allow bean removal. Excessive cylinder speeds will cause excessive splits and checking.
It is usually desirable to reduce the cylinder speed as the day progresses to compensate for additional drying. Maintain as large a concave clearance as possible and still do a good job of threshing. As beans dry down, cylinder or rotor to concave settings should be increased. Check your operators manual for recommended cylinder speed and concave setting. Manufacturers recommendations apply to average or normal conditions and may require variation to meet specific field conditions.
It may be necessary to harvest only in the morning and evening when the pods are tough in order to hold shattering losses to a minimum and reduce the number of split beans and checked seedcoats. Crowd the combine cylinder to near maximum capacity without overloading. To do this, either use a faster travel speed or put more rows in the windrow. The additional straw going through the threshing mechanism will help cushion the beans and prevent damage.
Set the adjustable chaffer at 5/8 inch and the sieve at 7/16 inch. This should allow the threshed beans and some hulls to fall through the chaffer, and the cleaning sieve will allow only threshed beans to fall through to the grain auger. Use a relatively high fan speed and direct the blast toward the forward one-third of the cleaning shoe. Check your operators manual for specific recommendations. Check the tailings return periodically to note the quantity and composition of the material being returned to the cylinder for rethreshing. Any appreciable quantity of threshed beans in the tailing return indicates that the adjustable chaffer is set too tight. Completely threshed beans returning through the auger for rethreshing will increase the amount of split beans and checked seedcoats.
Check the grain tank for dirt and foreign material and for beans that are split or have checked seedcoats. Excess dirt and chaff generally indicate that the adjustable sieve is adjusted too wide or that the fan blast is inadequate or improperly directed.
Excessive checks and splits generally indicate one or more of the following:
1. The cylinder speed is too high.
2. The cylinder concave clearance is too small.
3. Too many concave bars or grates are being used.
4. Too many completely threshed beans are being returned through the tailings system.
Most combine manufacturers have a number of optional accessories available for use on beans. These usually are bean sieves, screens placed in the grain pan and along elevator tubes. These help to remove dirt and foreign material from the beans.
Always handle field beans gently. Avoid dropping beans from great heights in unloading and handling. Beans check and crack when dropped, particularly on hard surfaces and when dry. Cushion or deflect the fall of beans whenever possible. Keep elevator flight chains snug so that flights do not ride on beans.
How fall frost affects dry beans
A killing frost is a temperature which kills the plant tissue. If you have frost (low temperature) damage, it is the result of tissue death. Critical stages and temperatures for dry beans and soybeans are described as follows:
Pinto and navy beans
Very sensitive to frost (30-32 degree F range). Earlier pods with yellow to brown color are sufficiently mature to escape damage. Late green pods or flowers are easily damaged by frost. Green beans will shrivel but should be left in field until dry in order to separate from mature beans.
Easily damaged by light frosts in the 28-32 degree F range. Beans that are still green and soft will shrivel. Stems rapidly turn dark green to brown and will not recover. Beans in pods that have turned yellow will mature normally. Some beans will turn yellow after 30-40 days of storage.