The multiple layer coating possibility provided by the Forberg rotating vacuum coater has an important impact on food quality and palatability.
In the past decade there has been great development in the
production of petfood diets made from extruded pellets. An
important part of the development is the addition of different
liquid additives such as digest improvers, vitamins, fat and
appetite improvers.
Palatability is a key factor in producing high quality
petfood. Besides involving a careful selection of
ingredients, it involves the right processing technique. The
multiple layer coating possibility provided by the Forberg
rotating vacuum coater (RVC) has an important impact on the
food quality.
Forberg International AS has been on the front lines with vacuum coating ever
since the process was introduced to the industry making
pelletized fish feed in the beginning of the 1990s. This
technique has made it possible to increase the level of energy
in the feed to new and higher levels.
It is of great importance to keep the pellets dry on the
surface even after adding the different liquids, and the
process of vacuum assisted intrusion of liquid in the pellets
is playing an important role.
To meet the requirements of the petfood market, some
adaptations to the RVC have been made (although dry petfood has
many of the same physical properties as fish feed, at least
concerning the ability to utilize the vacuum technique). These
include:
• The use of fat with a melting point higher than the
ambient temperature has triggered use of special heat cable
tracing of hoses to the nozzles and even tracing of the nozzle
assembly itself;
• Heat is traced and the coater body is insulated to
prevent build-up of solid fat in the machine;
• The machine housing and rotors can be made in stainless
304 or 316 depending on the level of acid addition.
The Forberg RVC is a machine that is especially developed
for using vacuum to improve the intrusion of liquids in porous
extruded pellets. Important features, according to the company,
include:
• Loading and unloading the machine through the same valve
minimizes the risk for leakage;
• Loading/unloading valve is out of the process area
during processing, ensuring what is put into the machine stays
there until the charge is ready for unloading;
• Smooth process chamber with accurately adapted rotors
ensures very low wear and breaking of the pellets during
processing;
• Total control of the vacuum cycle for the rate of
equalizing back to atmospheric pressure gives an optimum
capacity of inclusion;
• Easily included cleaning in place system allows thorough
and fast cleaning; and
• Machine is easy to change between formulas without
risking cross contamination.
After pellets have been loaded through the inlet valve of
the RVC, the valve is closed and the preset level of vacuum is
obtained. The next step is to add liquid additives through the
single-component nozzles on the machine while the rotors are
running. Forberg says the RVC's ability to fluidize the product
and its high internal transport capacity are the reasons the
distribution of the different liquids is possible at a high
level. This principle allows perfect distribution directly on
each pellet even for very small quantities of liquid additive,
according to Forberg.
After distributing the liquids onto the surface of the
pellets, the carefully monitored process of equalizing the
pressure inside the process chamber back to atmospheric presses
the liquid inside the pores of the pellets, leaving the surface
dry.