PET Food Processing - March 2019 - 48

EQUIPMENT

Cooling and drying product
before it is packaged is a
crucial step to eliminate the
possibility of condensation
or excess moisture, which
could decrease shelf life and
lead to mold growth.
Wenger Manufacturing

"One exception to this is basted-type products that improve aromatics and flavor of the treats. Typically, these
are very-low inclusion addition levels."

Multiple methods

"Most premium brands of pet foods will use several different types of coatings on their products," says Terry
Stemler, president, Automated Process Equipment Corp.
(APEC), Lake Odessa, Michigan. "This often includes a
type of fat or oil, a flavoring and a dry topical coating."
Manufacturers spread coatings using a coating drum
or a continuous blender with liquid usually applied first
in a uniform application to the outside of the product.
Batch coating systems provide processors optimized
coating uniformity, gentle product handling, high
precision and accuracy, and 100% cleanout, while continuous coating systems offer constant material flow
in a smaller footprint with a lower capital investment.
Vacuum coating systems use a differential in pressure
to force liquids through the outer layer into the porous
area of the pellet and can hold up to 35% of dry matter
weight, offering a no-dust, gentle-handling option.
The DFSC coating drum from Bühler offers a special
spray-pipe design and easy maintenance with multiple
couplings and the ability to simultaneously coat product
using up to three different liquids with a maximum
liquid addition rate of 8% of the product throughput.
Product is continuously fed through the inlet into the
coating drum and turned by flights. The adjustable
drum inclination conveys to the outlet.
The delivery of dry powders is typically accomplished
through a loss-in-weight feeding device with an auger
to the coater, scarf plate distribution tray and/or spinning disc applicators. Auger-type, paddle and reel coaters use different actions and speeds to control uniformity. Entry may be through a single point or a rectangular

PET FOOD PROCESSING | March 2019 | www.petfoodprocessing.net

entry, depending on the action of the coater, with
some systems using compressed air to deliver
a fog of powder into the coater.
Andritz, Graz, Austria, is adapting vertical
mixing elements to coating technology and
offering batch coating systems with or without vacuums. These systems possess high
spraying efficiency and flexibility when it
comes to batch size. The use of a vertical transport screw allows all the product to be exposed
over time at the top of the mixing vessel to ensure
uniform application of liquids or powders.
Equable delivery of liquid to all sides of the
product and subsequent tumbling and spinning
can assist with uniform coating. While hot liquid
and hot kibble absorb liquid better, product must
be appropriately extruded and uniformly dried to ensure equal absorption of liquids to the dried product.
The maximum coating without vacuum assist is 12%
to 20%, according to Keith Erdley, technical manager, Wenger. When the total liquid inclusion level is
greater than 15%, many recommend using vacuum
batch systems.
Different flow rates may demand multiple spray systems to ensure the liquid is atomized enough at various
rates. Nebulization systems disperse an atomized fog of
fat or oil for very-low inclusion levels of less than 1%,
applying liquids to dry solids using a spinning disk to
create a 360-degree curtain of dry product evenly and
accurately, negating waste through over-application.
APEC offers the Mistcoater Liquid Applicator that uses
spinning "dry discs" instead of spray nozzles to apply liquids with suspended solids to dry solids in a continuous
process. Multiple liquids can be applied through one inlet
point with less head pressure required of liquid pumps
because of the lack of liquid inlet restriction. The liquid is
atomized and applied to the falling dry material.

Measure and contain

"It's critical to have a good way to monitor the coating performance, measuring the liquid and dry forms,"
Stemler explains. "If using spray nozzles, monitor the
liquid pressure to make sure you don't have a plugged
condition. To determine if there needs to be more nozzles for more liquid flow, it's important to investigate the
specific performance curve."
A batch mixer operating under a vacuum works
well for coatings with very high liquid percentages,
allowing more absorption of the liquid into the kibble,
Stemler explains. Applying liquid first improves the adherence of the dry product, which might include the addition
of meat slurries dried to the outside of the product or antioxidants for preservation.

http://www.petfoodprocessing.net

PET Food Processing - March 2019

Table of Contents for the Digital Edition of PET Food Processing - March 2019