De-Hulling Soybeans: When To Do It & Why
Whether an animal feed oriented processor de-hulls their ExPress® soy or not is an economic/ strategic decision. Nutritionally, at least in swine trials, university studies show no significant advantage in amino acid digestibility for dehulling the soy prior to the ExPress® Process. For the processor, the value of the hulls is greater if the product is not dehulled given there is no adverse effect of the fiber when extruding.
On the other hand, some customers or markets demand de-hulled soy, so it is understandable why some choose to offer this product. So I thought I’d discuss a few of the principles of de hulling.
The combination of removing the hulls (fiber) from the soybean and the reduction of moisture thru the extrusion process, have the effect of increasing the protein of the finished meal. The amount of increase in protein is determined by several factors, including:
- How much oil the soybean has to begin with
- How much oil is recovered thru the ExPress® process
- How much moisture is removed during the process
- How well the pre extruded de hulling is done
The quality of de-hulling can vary widely, and typically you don’t get 100% of the hulls removed. Proper de-hulling involves drying the whole soybeans by one or two points of moisture, breaking the beans thru a roller mill and then running that thru an aspirator which separates the hulls from the meats. The reason for drying is to make the meaty part of the soybean shrink inside the hull, which makes for easier separation once it’s run thru the aspirator.
Setting the roller mill properly is also very important. You want to break the soy in to as few pieces as possible. The reason for this being that the aspiration parts of the process works on gravity. The cracked soy is dropped thru a chute with baffles that allows product to bounce back and forth on the way down while exposed to airflow that is pulling from the top, like a vacuum.
Airflow is adjustable so that the lighter hulls are separated from the heavier meats. If the roller mill is adjusted too tight it breaks the meaty part into smaller pieces that are lighter and can be lost in the hull stream. The roller mill needs to be adjusted to the point where there are no whole beans coming thru. Then the air in the aspirator needs to be adjusted for the least amount of meats coming thru in the hull stream. Sometimes you get a lot of size difference in the soybeans, which makes it hard to adjust. Even if you are seeing some half beans thru the roller mill you should be alright.
The de-huller should be checked and adjusted daily to insure a consistent finished product. Our sales team and nutritionists can help you through the decision process of whether to de-hull or not. But if you choose to de-hull we have the know-how to help you execute on the strategy.