Wenger's involvement in the Livestock Feed and Pelleting industry dates back
to 1935 when Wenger
developed and manufactured mixers, pelleting machinery, and other basic feed
milling equipment for the
livestock industry. Since this time Wenger has installed its pelleting technology
worldwide for use within
the livestock feed industry. The UP/C® (Universal Pellet Cooker) is Wenger's
latest technology for
production of pellets and pasteurization of mash.
In livestock feed processing plants, pelleting has become a primary processing
step to enhance the
quality of feed. It is a time-proven method of improving feed efficiency and
feed quality, which explains its
longevity in the field. Pelleting, the agglomeration of ingredients into dense
pellets, produces many traits
desired by livestock producers. These include:
- Decreased feed wastage
- Reduced selective feeding
- Improved feed efficiency
- Better handling characteristics
- Destruction of undesirable micro-organisms
- Increased bulk density
In the past, livestock producers have come to demand these qualities,
but as research reveals the
benefits of high temperature processing, feed manufactures are expected to
add to this list of desired
traits. High temperature/short time processing techniques, such as extrusion
and expansion, have added
new qualities to livestock feed that producers are requesting such as:
- Complete pasteurization
· Improved pellet quality (better durability and fewer fines)
liquid inclusion levels
- Improved feed utilization
- Increased starch gelatinization
- Production of by-pass fat and
The UP/C® (Figure 1) helps meet or exceed these
expectations. It is significantly more effective,
efficient, and versatile than the traditional systems,
such as the expander plus pelleting press (Figure
2) that are currently used. Since the UP/C®
utilizes fewer pieces of equipment, it is easier to
justify because it reduces capital, formulation,
operating, and maintenance costs.
RAW MATERIAL SPECIFICATIONS
Every feed production facility manufactures a
broad range of products. These can include several different diets for a single
species (integrators) or
several different diets for many species (commercial mills). Broad product assortments
require a vast
number of available ingredients to meet the nutritional requirements of each
specific diet. Since the
number of possible ingredient combinations is endless and selection is normally
based on least-cost
formulations, demographics, or nutritional value, the formulations may change
proper attention must be taken to ensure high quality pellets are consistently
produced. Ingredient grind (mean particle size) and formulation play a major
role in producing high quality pellets. These factors
similarly affect the UP/C® as they do other pelletizers.
Many researchers have studied the importance and effect of particle size reduction
performance. They have tried to determine the“optimum” particle size
to achieve maximum growth rates. The optimum size varies for each species,
age group, and selection of ingredients.
Researchers have found that the common thread in
particle size reduction is that a smaller mean
particle size will improve animal performance due to
an increased surface area available for enzymatic
attack. However, there are limitations to how fine
one can grind feed before health of the animals
becomes a concern.
Not only is particle size reduction important for
animal performance, but it is also very crucial for
pelleting. Coarse grinds create voids and fractures
in pellets making them sensitive to handling and
presumably to end up as fines at the feeder.
Evaluating particle size is commonplace in most
feed mills. Particle size is usually determined by
performing a sieve analysis. The feed particles are
separated by size, weighed, and the mean particle
size is calculated based upon a log-normal
distribution. Table 1 shows an example sieve
If the maximum particle size or foreign matter in the
feed is larger than the die opening, it is possible that
the opening can be plugged or partially blocked
resulting in a change of appearance of the pellets.
In cases of severe blockage, the pelleting die will
need to be cleaned before normal operation can
proceed. As a rule of thumb, when the desired pellet diameter is 4 mm or less,
the suggested maximum
particle size should be one-third the diameter of the opening (i.e. maximum particle
size of 1333 microns
for 4 mm pellets).
The UP/C® system, which utilizes the natural
binding qualities of the ingredient formulations to
their fullest extent, does not depend on the use of
nonnutritive binding agents to produce a durable,
high-quality pellet. These natural binding
elements of the raw material are starch, protein,
and fiber. Starch portions of the mix hold the
greatest binding capability. In most formulations
enough starch is present to produce the desired
pellet durability without giving much consideration
to the other two elements.
Starch possesses a unique ability to lose its
crystalline structure and become a viscous gel during processing. This allows
it to disperse through and
around structures of other origins. This loss of crystallinity is known as gelatinization.
Upon exiting the UP/C® and cooling, the starch returns to a crystalline state,
resulting in a durable structure. Between 50
to 80 percent of the starch fraction in most diets can be gelatinized during
Protein, like starch, can also function as a binder.
Protein denaturation is the modification of a
protein’s three-dimensional structure when
exposed to high temperatures. This threedimensional
structure is modified when the
proteins are subjected to mechanical and thermal
energy. The re-association, which aligns the
protein molecules, occurs during laminar flow and
forms a rigid structure. However, not all sources
of protein are good binders. Those sources with
low amounts of pre-processing, such as some
types of blood plasma meals, contain “functional”
protein which has a greater binding ability than
heavily processed sources, such as meat and
bone meal. Functional proteins are those that are
not already denatured.
Fiber strengthens pellets by “melting”. The
reassociation of the lignin present in fiber gives
binding power to the pellet. It takes much higher
processing temperatures to melt lignin than it does
to gelatinization starch or denature protein.
Therefore, its influence is often only low to
moderate in binding ability, yet high fiber diets will
typically form very durable pellets.
Processing principles of the UP/C® are different
from the expander and pelleting press. One
machine is designed to do the job of the
conventional two. A rotor and stator cook the feed similarly to an expander;
however, the feed is formed
into dense pellets rather than expanded chunks. With fewer pieces of equipment
required and less space
needed, the process flow is simplified.
The UP/C® system utilizes an initial cooking zone
so that the system depends less on mechanical
energy and more on thermal energy. This initial
cooking zone, known as preconditioning, is a
prerequisite for the production of quality pellets.
Preconditioning initiates the heating process by
the addition of steam into the feed. With Wenger’s
patented preconditioner (Figure 5), retention times
of up to 2 minutes are achievable. The Wenger
preconditioner exposes raw materials to steam
and water for longer periods of time than other
similar types of preconditioners. This allows the
steam to fully penetrate the feed particles.
Retention time and temperature of the exiting feed
are the two most important processing variables of
a preconditioner. These variables, which affect
Figure 3: Expander-Pellet Mill Flow Diagram
Figure 4: UP/C® Flow Diagram© 2001 Wenger Mfg, Inc. Sabetha, KS USA
66534 Page 5 of 11 the final product quality, must be monitored properly. For
example, when the feed throughput increases
both the retention time and the exit temperature will decrease, and fines in
the final product can result.
Thus to improve pellet quality, additional steam would be required to elevate
the exit temperature and to
provide an adequate level of cook.
Cook is the percentage of starch that has been
gelatinized during processing. Because gelatinized
starch has a proportional relationship with the amount
of heat exposure, it can be used as an indicator of the
final pellet quality. The Wenger preconditioner is
capable of cooking from 30 to 40 percent of the starch
present in a given formulation.
ROTOR AND STATOR
The rotor and stator are designed to convey feed
through a restricting plate, build pressure, and
increase the product temperature. The increased
temperature is the result of mechanical energy input or shear. This aids in the
cooking of raw materials.
The rotor consists of a segmented-flighted shaft designed to increase the internal
very quickly. Each segment of the rotor can be removed and replaced according
to wear of that particular
part. Since the whole rotor does not need
replacement, the wear cost is lowered considerably
The stator also consists of segmented parts. Each
stator segment has a wear sleeve that requires
replacement as needed. It is uniquely designed to aid
in the forward conveying of raw material. Shear bolts
or stop bolts, which are common in expanders and
need frequent replacement and maintenance, are not
required for the UP/C®
A pelleting die is required to restrict the flow of
material and provide the cylindrical shape of the pellet.
The number of orifices in the die is determined based
on the desired capacity, raw material formulation, and
final product specifications. Change-over time of
various dies is kept to a minimum due to their comparative light weight.
When a raw material formulation contains significant amounts of lipids, modifying
the pelleting die can
increase the pellet durability. Figure 6 shows how a die spacer can be installed
between the stator and
the die. This additional length increases the retention time of the raw material
inside the stator, in turn
increases the amount of shear on the product and thus creates a more durable
A variable speed rotary cutter controls the pellet length. For example, by increasing
the cutter speed
short pellets and crumbles are produced, and by reducing cutter speed longer
pellet lengths are
produced. This flexibility eliminates the need for crumbling rolls to produce
a crumbled feed.
Because heat and moisture are added during processing, extra equipment is required
to lower the
temperature, remove moisture, prevent mold growth, and prolong storage life.
The heat and moisture are
removed from the pellets by drying and cooling them after the UP/C®.
There are two types of coolers: vertical (counter current) and horizontal (Figure
7). Horizontal belt coolers
typically have a higher capacity than the vertical coolers. They convey feed
on perforated conveying
belts through the dryer. As the product moves through
the dryer, air flows through the bed of pellets. This
type of cooler is usually fitted with one or two
conveyors (single or double pass). The double pass is
more efficient than the single, since it requires less
airflow per ton of finished feed.
Vertical coolers (counter current or bin) allow pellets to
descend opposite the direction of the airflow. This
allows the coolest air to pass through the coolest
pellets and warmest air to pass through the warmest
pellets. This type of cooler requires less floor space
than horizontal coolers. Vertical coolers are typically
configured with one or two cooling decks depending
on the capacity requirements.
The UP/C® generally operates within the same
moisture constraints as other pelletizers. Exit
moistures reach a maximum of 18 percent. This
requires a cooler capable of driving off at least three to
six percent moisture to achieve a final moisture of 12
percent or less and cool the pellet to within 10°C of
ambient temperature. In situations where a
conventional cooler will not provide adequate moisture
removal a dryer will be required.
The advantages of topically coating feeds can include:
decreased dust, increased palatability, and increased
feed intake. Pellets can be coated with nutritive
ingredients such as fat, molasses, lactose, vitamins,
enzymes, or a combination of these and other
Coating equipment consists of an applicating reel, liquid tank, and a pump (Figure
8). For fat application,
the reel can be fitted with steam coils and a shroud to
prevent build up of congealed fat and fines.
To this point, both thermal and mechanical energy
have been loosely defined, but it is important to
understand how these process variables affect the
UP/C® process. Production of quality livestock feed
depends on many processing variables.
Pasteurization and production of durable pellets
requires the addition of steam and/or water in the
preconditioner to increase product moisture from 14 to
18 percent and a temperature of 70° to 90°C. The
shear provided by the rotor, stator, and the pelleting
die can elevate the product temperature to 115° to
170°C depending on the die configuration and
The UP/C® system offers two opportunities to pasteurize pelleted feed products.
The first stage is the
DDC preconditioner. As previously mentioned the DDC is capable of holding the
feed for up to two
minutes and can reach temperatures of 90º to 95ºC. This combination
of temperature and retention time
will destroy many microbial populations. Table 2 illustrates the ability of the
DDC to destroy some of
The second opportunity to destroy
microbes is in the UP/C® rotor and stator.
The technological concept behind the
UP/C® differs somewhat from the
currently used methods of heat treatment
processes. Other methods depend on
high temperature/short time (HT/ST™)
processing, meaning the feed spends a
relatively short amount of time (i.e., 20 to
30 seconds in an extruder and 15 to 25 seconds in an expander) at conditions
of high temperature and
high pressure. However, the UP/C® utilizes High Temperature/Micro Time (HT/MT™)
meaning feed spends a much shorter
amount of time under these conditions,
usually three to four seconds and still
reach temperatures of 125° to 170°C.
This ability to cook feed quickly, ensures
that heat sensitive nutrients such as
vitamins and amino acids, are handled
more delicately to prevent degradation.
However, harmful microorganisms, such
as salmonella, are destroyed.
Table 3 shows various heat sensitive
nutrient retention and microorganism
destruction in feed produced on the
UP/C®. In each case none of the
nutrients were degraded, but the
detrimental microorganisms were
destroyed. Table 4, shows the results of expanding plus pelleting on vitamin
retention. This data shows
that the expander does partially destroy some vitamins.
The ability for the UP/C® to produce an extremely durable and dense pellet
is illustrated in Figure 9. This
graph shows how the raw material viscosity changes inside the preconditioner
and stator as energy and
moisture are added. When energy inputs are sufficient and the product temperature
moves above the
glass transition temperature (Tg), major components of the raw material, such
as protein and starch,
transform from a highly viscous, glassy state into a rubbery dough. This change
begins to occur in the
As the temperature continues to rise inside the stator, the product reaches its
melt transition temperature
(Tm). When a product is heated above its Tm the rubbery mass’s viscosity
declines quickly and becomes
a fluid.4 The reduction of viscosity allows the raw material to pass through
the orifices of the die with
relative ease at low moisture and pressure (i.e., 200 to 900 psi).
Upon exiting the pelleting die, the pellet’s temperature declines and some
moisture flashes from the
surface of the pellet. The pellet returns to a
glassy structure. This reassociation and
hardening of the melt can be witnessed
when examining hot pellets exiting the
pelleting die. At this point the pellets seem
fragile, but after cooling they become very
strong and durable. Since each feed mix
has a different Tg and Tm, each feed
formulation will process differently.
To further clarify this, consider the feed mix
as a mass of wax. At room temperature it is
in a crystalline state, but when heated the
wax becomes pliable. The temperature at
which the wax shows a considerable
amount of flexibility, could be considered as
its Tg. Continuing to heat the wax will
eventually convert it into to a fluid, so the
temperature at which it fluidizes can be
considered its Tm.
Figure 10 shows photos of a pelleted feed made using a conventional expander
plus pellet mill process
and one from the UP/C® system, magnified with a scanning electron microscope.
Notice the laminar
structure that develops with the UP/C® process. It provides superior strength
over the expander plus
pelleted product, which does not have this same structure
FINAL PRODUCT CHARACTERISTICS
Every livestock producer has different ideas for what the appearance and quality
characteristics of feed
should be. These specifications include: pellet size, bulk density, durability,
fines content, moisture, and
other various considerations.
These product specifications can be
controlled by the independent
processing variables of the UP/C®,
which include the following:
- Feed Delivery Rate
- Knife Speed
- Pellet Die Configuration
- Recipe Formulation
Pellet size can be easily controlled.
The possible pellet diameters range
from 2 to 18 mm and adjustments
are made by a quick and easy
replacement of the pelleting head. The pellet length can be varied to any size
or even into crumbles
when desired by adjusting a variable speed cutter and/or varying the number
of knife blades.
Bulk density can also be controlled and varied during operation. However, pellet
diameter and length do
have a significant effect on the density range. As the diameter and length increase,
the bulk density
decreases. Typically the bulk density of UP/C® pelleted feeds is about 550
to 650 grams per liter.
The raw material affects the finished product density to the greatest extent.
High fiber diets tend to have
the lowest raw material densities; therefore, one can not expect to achieve the
same finished product
density as a feed high in protein or starch.
Durability is probably the most important characteristic of pelleted feed. Consumers
expect the most
durable pellets possible. Poor pellet durability results in the generation of
fines. Durability can be
predicted by determining the Pellet Durability Index (PDI)7 (Appendix A), which
gives reference to how
well pellets hold their integrity during packaging and handling. The U P/C®,
however, typically produces
pellets with a PDI of over 95 percent.
Studies with swine have shown that pelleted feeds with 10 to 15 percent fines
can negatively influence
animal performance. The findings show that as the fines content increases feed
wastage, low palatability,
and lower feed conversion ratios are noted. Fines create waste at the feeder
and are not as palatable as
Several factors influence the ability of the UP/C® to prevent the production
of fines. Mean particle size,
diet formulation, and starch gelatinization all affect the production of fines.
Large feed particles can
disconnect from the pellets as the cutter shears them to length at the pelleting
head. Low levels of cook
lead to poor pellet durability and inevitably lead to the breakdown of pellets.
Also, high fiber diets tend to
produce more fines than high starch diets, since these ingredients have different
BENEFITS OF THE UP/C®
The UP/C® has shown advantages over pellet mills and expanders in several
feeding trials with poultry,
swine, and dairy cattle. Table 5 shows the advantage of a UP/C® for poultry.
Those animals feed pellets
produced on the UP/C® reached grown weight more quickly and needed less feed
to reach the target
Other than the mainstream production of compound feed, the UP/C® can also
produce types of feeds that
are all but impossible for pellet mills and expanders to produce. Full fat soy
(FFS), soft-moist pellets, and
feeds high in by-pass protein and by-pass fat are the most notable.
FFS production has been
limited to HT/ST™ extrusion
systems due to the high energy
input requirements needed to
destroy the anti-nutritional
factors that exist in raw
soybeans. However, the UP/C®
has shown to be very capable
of producing equivalent quality FFS. Figure 11 shows the results of four tests
run at different specific
mechanical energy levels (SME). At the higher SME inputs acceptable product can
Destruction levels between 80 to 90 percent are found to be sufficient for trypsin
inhibitor in most livestock
Production of soft-moist pellets are an available option with the UP/C®,
giving feed producers even more
flexibility to satisfy consumers and open new markets. With the proper ingredients
included in the
formula, final moisture and mold growth will not be a concern. The final moisture
can vary from 15 to 20
percent when humectants and mold inhibitors are included in the ingredient mix
to control water activity.
By-pass protein and by-pass fat are characteristics of heat-treated feeds that
producers of ruminant
animals desire. By-pass protein is the result of denatured protein. The protein’s
reduction in solubility,
allows the protein to “by-pass” or escape the rumen and be digested
in the small intestine. By-pass protein can be measured by determining the Nitrogen
Solubility Index (NSI) (Appendix B) of the
processed feed. The NSI value represents the amount of protein that is soluble;
therefore, the remaining
protein is considered insoluble or by-pass protein (i.e., NSI value = 20 percent,
by-pass protein = 80
Lipids included in feeds specified for ruminant animals can interfere with fiber
digestion and even destroy
necessary microorganisms that
aid with fermentation in the
rumen. However, by-pass fat
escapes the rumen without
interfering with the fermentation
process and is allowed to be
digested downstream. By-pass
fat is the result of the formation of
a complex between fat and starch
or protein that occurs during high
temperature processing. It can
be quantified by determining the
difference between the Acid
Hydrolysis method (AH) and the
Ether Extract method (EE) of fat
analysis (i.e., AH - EE = by-pass
fat). The ether extract method
cannot measure fat that has
complexed with starch or protein,
therefore, it will be the lesser of
the two values.
Feed manufacturers have been bombarded recently with technological advances in
the compound feed
processing industry. As with any technology, however, continuous development
brings about major
improvements. The UP/C® is a direct result of the rapid increase in demand
for processing equipment
required to heat treat and pelletize livestock feeds.
The UP/C® enables feed producers to provide high quality feed with the ease
and simplicity of using one
machine. The flexibility provided allows producers to gain greater customer satisfaction
new characteristics into existing feed lines at lower cost. The UP/C® is
the machine of choice for
producers looking toward the next generation in pelleting technology.
Wenger Livestock Feed Process Team
Galen Rokey, Manager, Wenger Technical Center
Rob Strathman, Director Technical Service
Brian Plattner, Process Engineer
1 Rokey. G. 2001. Pelleting, Conditioning, and Steam Addition. 2001
Feed Management Seminar. US
Egg and Poultry Association. Nashville TN.
2 Wenger Technical Center Test Data. 1996
3 Coelho 1994. Vitamin Stability in Expanders. Feed Management. 45(8). 10-15.
4 Strahm B., B. Plattner, G. Huber, and G. Rokey. 2000. Application
of Food Polymer Science and
Capillary Rheometry In Evaluating Complex Extruded Products. Cereal Foods World.
5 Strahm B. and B. Plattner. 2001. Put the right tools in your toolbox
to ease aquafeed extrusion. Feed
Management. 52:3. 19-22.
6 Strahm B. and B. Plattner. 2000. Thermal Processing: Predicting
processing characteristics of feed
materials. Feed International. 21:4. 26-29.
7 Pellet Durability Index - Laboratory Procedure. 1994. Feed Manufacturing
Technology IV. R.
McEllhiney, ed. American Feed Industry Association, Arlington, VA.
8 Wenger Technical Center Test Data. 2000. Feeding trials by independent third
9 Wenger Technical Center Test Data. 1996.
Laboratory Procedure - Pellet Durability Index
The following procedure is for measuring the durability of feeds to indicate
their ability to withstand
2. Sieve with openings just smaller than nominal pellet diameter
3. Tumbling device
1. Weigh a 500 gram sample of pellets. (mbefore)
2. Place pellets in tumbling device and tumble for 10 minutes.
3. Sieve sample to separate fines retaining large pellets on top of sieve.
4. Weight pellets remaining on top of sieve. (mafter)
5. Calculate sample pellet durability:
Source: Feed Manufacturing Technology IV., 1994. R. McEllhiney, ed. American
Association, Arlington, VA.