Pelleting versus extrusion for shrimp feed manufacturing
by Nils Lastein, Global Application Manager, Andritz, Denmark
For shrimp feed to have the desired effect—that is to provide optimal energy for maximum growth—it must meet the following characteristics: Shrimp feed pellets must achieve 100 percentsinkability and have a water stability greater than two hours.
However, the starch is used to hold pellets together has no real nutritional value for shrimp. Therefore, a process that allows for starches to be replaced by protein can further support the goal of an optimised feed conversion ratio.
However, there are quite a few additional factors to consider when determining the best process solution for your shrimp feed manufacturing facility. Shrimp feed can be produced either by pelleting or extrusion, and each of these processing techniques has its pros and cons. Here we make a side-by-side comparison to help processors determine the best course of action for their individual facility and circumstances:
When pelleting, grind quality is very important. When oversized or inconsistent particles are encountered in the feed ingredients, pellet durability is adversely affected. While both processes will benefit from the addition of grinders or pulverisers, when choosing the pelleting process for your shrimp feed production, consider the addition of classifiers for the processing of recycling oversized particles.
The pelleting process is highly sensitive to excessive moisture content; high moisture causes rollers to slip and consequently creates machine blockages.Therefore, post-conditioning is a necessary step in the pelleting line, in order to achieve a suitable level of starch cooking, and to meet the requirement for water stability.
Pelleted feed is a densification process by nature and, therefore, coating feed with liquid palatants or wet nutritional ingredients (fats and oils) post-pelleting can be a challenge. Another factor that affects pellet quality is control of pellet size and length, which poses additional process challenges.
While there are challenges with producing a high-quality shrimp feed pellet on a pellet mill, the process is a long-standing industry technique making hiring and training accessible.
Intensive pre-conditioning is a decisive stage of the extrusion process. To prevent expansion of pellets out of extruder the meal ingredients must be kept at a precise temperature. Additionally, because of all the excess moisture added during both preconditioning and extrusion, drying is also mandatory so moisture stability can be maintained in the finished pellets. However, post-conditioning can be eliminated from the extrusion process altogether.
Several benefits of extrusion include precise control over pellet length, a factor that is important in starter feed where pellets should be as small as Ø0,6mm. This process is not possible on a pellet mill without the addition of a crumbler. In addition, control over pellet porosity means they can be easily coated with palatents and oils.
The extrusion technique also allows for substitution of functional starch with nutritional proteins and the expansion control system® allows feed producers to precisely adjust the pellet expansion obtaining full and complete sinkability, the two primary factors for production of high-quality shrimp feed.