PET Food Processing - March 2020 - 58

EQUIPMENT

Preconditioners
maximize the capacity of extruders, bring
more thermal energy
into the process,
and reduce wear on
extruder parts.
Clextral

BENEFITS OF
PRECONDITIONING

* Improved moisture
penetration
* Improved heat
transfer
* Improved mixing
of wet and dry
ingredients
* Decreased
friction and
wear of extruder
components
* Higher extruder
capacities
Source: Wenger Manufacturing, Inc.

58

also allowing for the ability to vary retention time within
the preconditioner.
Maximum efficiency of a preconditioner is attained
when it is running at the lowest possible CV and creating the most homogenized mix of ingredients. "In short,
the design of the preconditioner should create the most
'chaos' possible and still maintain FIFO [first-in-firstout] as much as possible when it comes to retention time
distribution of the mix, which will, in turn, provide for
the highest level of homogenization of the mix as it enters the extruder barrel," Martinez-Kawas says.
Lavocat explains that "Clextral's preconditioner has
a proprietary design to ensure homogenous mixtures:
a filling control device with a specially-designed screw
inside the tank that favorably modifies the flow by enabling a partial and controlled recycling of the material
being processed, from the outlet to the entry point. This
action intensifies the mixing functions and maximizes
heat and mass transfer, in particular in the first third of
the mixing chamber which is the preferential zone for
steam injection. To achieve this, the various adjustable
water and steam injection ports have been positioned
- axially and angularly - to enhance absorption and
product exposure time during the mixing stage."
Marcel Ramseyer, head of market segment pet food,
Bühler Group, Uzwill, Switzerland, says that a preconditioner with a two-chamber design offers a major advantage, allowing both independent mixing uniformity
and independent retention time. Additionally, "an easily
accessible and hygienic design enables fast and proper
cleaning procedures," he says. "This helps ensure food
and feed safety, as well as increases productivity by
reducing cleaning and changeover time, and the need
for maintenance."
Food safety is also supported with design features that
manage fugitive dust and moisture. "Modern recipes often look to incorporate ever-increasing levels of moisture
due to the addition of meat slurries," Tramp says. "If this

PET FOOD PROCESSING | March 2020 | www.petfoodprocessing.net

moisture and product particles are allowed to escape
the preconditioner, it can present significant sanitation
challenges in the surrounding area. The most modern
preconditioning technologies look to address this issue
through maximizing the direct injection of steam into
the product while simultaneously protecting against
particles being allowed to vent from the preconditioner."

Perfect partners
For certain applications, both product output and quality are considerably enhanced by the use of a preconditioner prior to the extruder.
"Preconditioners are widely used for extruded pet
food kibble production in order to maximize throughput of the extrusion unit and the quality of the pet kibbles," Lavocat says. "Typically, preconditioners are not
used for pet treat manufacturing."
Martinez-Kawas says preconditioners are paramount
for recipes with moisture above 18% such as the highmeat and high-fat specialty products found in the market today. "Without the preconditioning step, uniform
distribution of moisture will likely be compromised,
resulting in opportunities for clumping, out-of-spec
product and discoloration of the final product," he says.
Although product is warmed in preconditioners, the
kill step or final cook temperature is typically reached in
the extruder.
"Broadly speaking, the target temperature (in preconditioners) is from ambient to 100 C, and the target
moisture levels are highly recipe-specific but range
from native to 30%, in some cases higher," Tramp says.
For food safety, modern extruders are considered the final critical control point, so it is advantageous to have
zones separating them from the downstream process,
Tramp explains.
Quality preconditioning devices play an important
role in the uniformity of the recipe as it enters the extruder cooking step. "The more uniform the ingredient
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