While we all accept, understand and agree that steam is the only thing that contributes to all three elements – temperature (sensible heat), heat (latent energy or heat), and moisture required to condition the mash meal before going for pelleting. Requirement of these three elements vary according to local ingredients, meal temperature, and meal moisture including other environmental factors.
In some parts of the world (mostly temperate regions) or at a particular time of the year, meal moisture gets quite high so we need to focus more on temperature and heat from the steam. While in other places, meal temperature gets too high and ingredients are so dried up (in tropical regions) that we require more moisture by pulling in low temperature high saturated steam to manage extra conditioning time and before reaching setting conditioning temperature fast. In some conditions, both temperature and moisture of the ingredients is so low that we require all three elements-temperature, heat and moisture of steam to condition the meal properly. It is not desirable to have a single operating setting parameter for running the pellet mill, as all the three elements mentioned above are closely related to each other for the successful pelleting operation.
Hence, it is of utmost importance to work with the correct steam type that provides a fine balance of these three elements, as per the requirement of meal ingredients and the mill operator should be trained to work dynamically.
In case, steam is not able to contribute enough moisture in dried-up conditions to properly condition the starch rich diets as required for feed manufacturing, we may add moisture through water in the mixer. It is necessary to provide sufficient moisture as enough hydration is the key in starch cooking and properly conditioning the mash meal before it enters the pellet press.
So, the primary objectives of proper meal hydration during conditioning are to:
• Ensure uniform moistening of feed particles – Adding sufficient water in mixer or sufficient steam in conditioner, helps to moisten the feed particles uniformly which if offered sufficient time (inside the conditioner), helps this water to penetrate inside the feed particles with enough agitation in the form of paddle rotation which also depends on the particle size (at this point of time, we have to remember while it is very easy to transfer temperature and heat from the steam to the feed particles, it is the moisture which is the most difficult to get transferred and that is the reason that we always advocate for a long time conditioner with minimum 40-60 seconds of conditioning time).
• Initiate the cooking process – the cooking reaction is primarily a function of temperature and time, in the presence of sufficient water. If any of the element is missing, feed will not get properly conditioned to produce desirable quality of pellets. Enough conditioning with right quantity of moisture in the mash meal in conditioner also helps the starch gelatinization process to get completed in the die.
Note that in this discussion, cooking, conditioning or starch gelatinization are being used as interchangeable generic terms to describe the various material transformations, which occur during the feed processing to form pellets or crumbles.
Benefits of Proper Hydration:
Achieving required hydration softens particles and reduces die wearing. As water is part of the cooking reaction, uniform hydration also enhances degree of starch gelatinization that means more leaching of amylose to bind other feed particles. Gelatinization enhances the ability of starch to absorb large quantities of water and this may lead to improved digestibility and improved feed conversion efficiency (a starch granule can hold up to 300% moisture than its weight).
By achieving required degree of cooking, digestibility of the pellet is improved. Gelatinization increases the speed of enzymes (amylases) to break down the starch linkages, thus, converting it to simpler and more soluble carbohydrates as higher gelatinized starch or feed gets faster digested and assimilated in the bird’s body. A high degree of cooking also means that binding and pellet durability can be achieved with less starch (with protein binding also contributing to the protein quality). If cooking is initiated in the conditioner, less cooking needs to be done in the die chamber, which may result in improved throughput. But also, in a conditioner, the cooking is achieved under relatively low shear conditions (low mechanical energy) compared to cooking in the extruder barrel – so reduced water solubility and higher water absorption in the product also enhance pellet durability after it is wet.
by Dr Naveen Kumar, Delst Asia