Dr Naveen Kumar, Delst Asia
Feed processing refers to the treatment of feed prior to its consumption by animals. In general processing consists of steps such as grinding and mixing, or a series of steps including grinding, mixing, conditioning, pelleting and cooling. The core process in most feed mills is the pelleting operation, where a mash feed prepared from a mixture of ingredients, such as grains, protein sources, minerals, vitamins with other feed additives, according to a specified formulation is pelleted in a roller-and-die press mill. Most of the time oil or/fat and water is also mixed in the formulation either to increase its energy value, pelletability, lubricity or to reduce the moisture loss (also called processing loss or production shrink) during the process. A binder may also be added to the feed if adequate pellet quality is not obtained through proper steam conditioning and die selection. The artificial binders add to the cost of feed and should only be used or considered when all other means are exhausted. Once the ingredients are mixed and transferred to the bin, before entering the press, feed flows into a feeder which moves the feed at desired rate into a chamber, called “Conditioning Chamber” or “Conditioner” where the feed is conditioned with steam at a fixed temperature.
An ineffective conditioning process causes more problems with the pelleting operation in many commercial feed mills than anything else. Also contrary to the general belief among feed millers, pellet quality is primarily established in these Conditioners rather than in the pellet die and steam conditioning is the most important element in achieving high quality pellets at high production rates at a low cost in these conditioners. Right conditioning is mostly dependent on two dynamics Design of Conditioner and Steam Quality.
Serving the purpose of this column to discuss the role of conditioner in producing good physical pellet quality, my major focus would be on highlighting various features of conditioners to suggest our readers on selecting a right conditioner for their feed mill. Also I would like to highlight that a very little peer-reviewed literature appears to exist on the subject of role of differently designed conditioners on pellet quality, more so in the tropical conditions like Indian-subcontinent. Steam generation, control and quality maintenance may be discussed in details in the coming issues to illustrate its effect on mash conditioning and pelleting.
A Right Conditioner
In the previous issues, we have understood about the importance of cooking the raw starch effectively, available in different plant ingredients, through this process of pelleting for better pellet quality. And this effective cooking is achieved through effective conditioning that further depends on the right conditioners and a properly designed, maintained and operated steam supply system. This conditioner is definitely the most important element of the feed pelleting process, and an obvious tool to get the job done effectively. Below are the important features for a right conditioner:
1. Sufficient steam inlets allowing sufficient volume of low pressure saturated steam entering the conditioner.
2. Maximum fill ratio inside the chamber fully utilizing the injected steam for effective steam/mash infusion.
3. Sufficient paddle shaft agitation with minimum 60 seconds residence time for effective steam/mash interaction. It has been suggested that as the hydration time of the feed particles is much longer than the time required to heat them, hence the residence time of feed inside the conditioner should be based on the time required for adequate hydration, not the time for adequate heating. This is where the current engineering norm for steam conditioners has gone wrong. We need to work with saturated steam at a temperature closer to saturation point, with a long residence time of 60-70 seconds for maximum infusion of steam into the meal, and allowing for proper swelling of raw starch granules.
Unfortunately, not many conditioners in the market can fulfill these important criteria. Do take note that the long Retentioner or a Hygeinizer is just a slow screw transporter and do not contribute to any agitation, or proper steam/mash interaction. The Hygeinizer has not been engineered with much consideration or priority to raw starch cooking.