Evaluating factors impacting enzyme recovery in pelleted feeds

Feed processing conditions vary dramatically between feed mills, and pelleting temperatures and conditioning times have increased in recent years to meet the demands for ever greater levels of feed hygiene and pellet quality. In this article, AB Vista’s Americas Feed Application Engineer, Joel McAtee, explains how conditioning temperature, retention time, die specification and pellet cooling all play an important role in ensuring optimal enzyme recovery and pellet quality.

Conditioning temperature

The addition of steam in the pelleting process involves both high temperatures and moisture levels, as well as the dwell time of feed in the conditioner, which can have a direct impact on enzyme recovery. As conditioning temperatures and moisture levels increase to meet the principle demands of feed hygiene and production requirements, enzymes can become “active” which can make them unstable, including coated products. Therefore it is important to continue to evaluate and monitor the feed conditioning process to optimize enzyme recovery.

Retention time

Retention time is dictated by overall chamber length, pelleting capacity, auger tip speed and pick angles. Steam quality plays a role in maintaining temperature and moisture levels within the feed. The quality of steam depends on the percent vapor and the equipment responsible for controlling that vapor. Factors including boiler operation, fittings, positioning of pressure regulator, pipe diameters, steam traps and separators that eliminate surges of condensate to the conditioner, can all impact the quality of steam delivered and thereby enzyme recovery.

Once the steam is delivered to the conditioner the injection of steam and the subsequent application to the mash needs to be such to allow the steam to transfer its energy in an efficient manner. Longer retention times will afford a higher degree of heat and moisture transfer, which can under some circumstances lead to a reduction in in-feed enzyme recovery.

If your goal is to reach an optimum moisture level to soften the feed particles to improve compaction and lubricate the mash to avoid die friction, it may be more advantageous to add water at the mixer as opposed to applying wetter steam at the conditioner. In return, the added moisture and bound moisture levels will be sufficient, and conditioning/pelleting at 80-85°C / 175-185°F will produce a quality pellet without impairing enzyme loss even when using coated products.

Die specification

Pelleting equipment such as the specification of the die can also have an influence on enzyme recovery. Each feed requires a die with the appropriate resistance to ensure it meets its respective quality specifications. Die resistance is based on the length/diameter ratio requirements. A higher L/D ratio causes more compression and higher die retention time which in turn causes more frictional heat through the die. More frictional heat can have a deleterious outcome on enzyme recovery.

Understanding your formulation, production rates and desired pellet quality will help you ensure optimal die selection.

Pellet cooler

Another aspect in the feed pelleting process that can often be overlooked when evaluating enzyme recovery is the pellet cooler. Pellet cooling is a dynamic process that involves excess moisture being removed from the feed by evaporation. Convection cooling can also occur and depends on the amount of pellet surface area, and the temperature difference between the pellets and the air.

Ensuring that there is a decrease in moisture along with temperature in a uniform process is important in ensuring enzyme recovery – the high priority is lowering moisture quickly to stabilize the feed which can limit mold growth and improve enzyme activity.

Many variables affect the pellet cooling system including air temperature, relative humidity, and the volume and velocity of air passing through the equipment. Product factors that can mitigate the process would be temperature, moisture content, pellet size and density, fines present, and pellet quality. Variables in the cooler include product bed depth, uniformity of bed depth and system design.

To ensure suitable storage and handling of pellets the cooling system must be designed to effectively cool a range of products by removing sufficient moisture and heat whilst also avoiding over-drying the pellets. Regardless of the cooler type it is important that the bed depth is uniformly distributed in order maintain a constant and equal flow of air through the product.

Evaluating the conditions in your feed processing plays an important role in ensuring optimal enzyme recovery and pellet quality of processed feed. Conditioning temperature, retention time, die specification and pellet cooling vary significantly between mills and all play an important aspect in meeting quality specifications, which should not be overlooked and should be reviewed several times per year.