1. TECHNICAL
36 ASIAN FEED MAGAZINE – February/March 2016
Introduction
Recent research have shown a
low extent of starch gelatinisation
in pelleted diets, due primarily to
the limited amount of moisture
and insufficient amount of steam
applied in steam conditioning from
conventional pelleting process. Proper
steam conditioning contributes
to effective cooking of raw starch,
enhances the performance and
productivity of a pellet mill, and
contributes greatly to the pellet feed
quality and feeding value to the
animals. As a first step, we need
to understand what steam to work
with for different diets in different
climatic conditions, to effectively
cook raw starch. Working with a well-
engineered conditioner to serve the
purpose is crucially important too.
Steam for feed pelleting
Steam provides both heat and
moisture to the meal, so that the
meal is in the most suitable condition
for the formation of pellets. The
added steam will increase the
moisture and temperature of the
meal entering the press chamber
and through the die when most
starch gets cooked. To optimise the
conditioning process, the proper
balance of heat and moisture must
be obtained. The objective of steam
injection during conditioning is to
improve binding characteristics
through gelatinisation of starch,
and polymerisation of proteins for
better enzyme digestion. These
Role of proper steam conditioning
– feed pelleting efficiency &
feeding value
Proper steam conditioning provides the bridge to feed
pelleting excellence and may provide some direct link to
animal health and productivity. STEVEN GOH* discusses
approaches to effective steam conditioning for the best
compromise between feed pellet quality, machine throughput
efficiency, and feeding value of the processed pellet feeds.
chemical changes produce sticky
and clinging substances, which bond
to the less reactive materials and
hold the mass together. Realistically,
we need to achieve about 16.5%
moisture after steam conditioning
(when the conditioned meal exits the
conditioner). The industry, however,
is typically only achieving between
13% - 14.5% moisture up-take after
steam conditioning. The consequence
is poor pelleting efficiency, poor
pellet/crumble quality with lots of
fines, low moisture pellet feed, poor
feeding value, and production shrink
(moisture loss).
Steam contributes three elements
- temperature (sensible heat), heat
(latent energy or latent heat), and
moisture. These three elements are
closely related and you can’t get one
without another. It is important to
work with the correct steam type that
provides a fine balance of these three
elements. This is the key to “steam
management“.
There is a difference between
steam temperature and latent
heat. What we need from steam
to effectively cook raw starch is
“Latent Heat“ and “Moisture“.
Saturated steam (with temperature
of 102 – 105˚C) condenses readily,
giving up moisture and latent heat.
Figure 1: Steam conditioning.
Note: Gelatinisation heat depends on the starch source. Gelatinisation heat of wheat starch (10.05
joules/g) is lower than maize (13.82 joules/g). This means for every gram of wheat and maize
starch to be gelatinized, 10.05 joules and 13.82 joules of heat are required, respectively. High-
amylose content cereals are more resistant to gelatinisation during processing than those with
normal and high amylopectin cereals. ‘Flint corn’ in regions like India, Philippines, Myanmar and
Indonesia are also more resistant to gelatinisation compared to the ‘Dent corn’ from USA, South
America and China.

2. ASIAN FEED MAGAZINE – February/March 2016 37
This paper was presented at the
Bangkok, Thailand 3–4 September 2015
Figure 2: Micro steam management.
Super-heated steam with very
high temperature (130 - 140˚C) is
reluctant to condense, and is the
reason that meal is insufficiently
heated or moistened.
Latent heat is defined as heat
absorbed or released as water
changes between a solid, liquid and
gas. In contrast to latent heat, steam
temperature is sensible energy or
heat caused by processes (pressure
applied at the boiler) that do result in
a change of the temperature of the
system (steam generated at varying
pressure). Heat is thermal energy
in the process of transfer between
a system and its surroundings or
between two systems with a different
temperature.
A good way to remember the
distinction is that a change in
sensible heat may be sensed with a
thermometer, and a change in latent
heat is invisible to a thermometer
(the temperature reading doesn’t
change).
Enthalpy of water at 100˚C is
419 kJ/kg. When water is cooled
down from 100˚C to 0˚C, 419 kJ
will be released. At atmospheric
pressure (100 kPa), when the
water temperature reaches 100˚C,
the heat being added will no
longer increase its temperature,
because the water will evaporate
into steam. This change of state
requires a considerable input of heat
energy (enthalpy) of evaporation.
To change water of 100˚C into
steam of 100˚C, the enthalpy of
evaporation is 2,257 kJ/kg. So the
heat content of steam or enthalpy
of steam (at atmospheric pressure)
is equal to the enthalpy of water
plus the enthalpy of evaporation or
419 + 2,257 = 2,676 kJ/kg. This
emphasises the considerable amount
of heat contained in steam, which is
why steam is such a useful heating
medium.
Condensation is the opposite
process of evaporation. Latent heat
of condensation is energy released
when water vapor condenses to
form liquid droplets. The temperature
does not change during this process,
so heat released goes directly into
changing the state of the substance.
The energy released in this process
is called heat of condensation. The
heat of condensation of water is
about 2,257 kJ/kg. The heat of
condensation is numerically exactly
equal to the heat of vaporisation, but
has the opposite sign. In the case of
evaporation, energy is absorbed by
the system (the steam); whereas in
condensation heat is released, and
this is the “latent heat” that we need
for raw starch cooking.
Steam conditioning plays a much
larger role towards cooking raw
starch, especially the amylose fraction.
Condensing steam provides the
criteria (sufficient amount of latent
heat and microscopic moisture from
the condensing steam to get the job
done effectively. The clue here is to
work with saturated steam - steam
that enters the conditioner at close
to condensing temperature (102˚C
– 105˚C max.). On the contrary, the
industry is often working with super-
heated steam that has a much higher
temperature (130˚C-140˚C), and
the consequence is poor moisture
uptake after steam conditioning and
improper cooking of raw starch.
The solution is to re-engineer the
conventional steam-piping set-up to
generate saturated steam entering
the conditioner at 102˚C - 105˚C
consistently at working load. To
do this successfully, we need to
understand steam thermodynamics.
The entire steam piping layout has
to be engineered to allow steam
to conform to its thermodynamic
behavior without causing any
moisture leaching at low pressure
setting or affecting sufficient steam
flow (volume) into the conditioner at
low pressure setting.
Saturated steam provides much
lesser sensible energy and much
more latent heat and moisture. Latent
heat and moisture is released from
saturated steam the moment it starts
condensing at 100˚C. Latent heat
and moisture are needed to soften
and swell the starch granule, to
effectively cook the raw starch matrix
- in particular the amylose fraction
that provides the gelling effect. It is
important to achieve a high level of
starch gelatinisation for intra-particles
bonding to form a good pellet.
Invariably, this will also improve feed
pelleting efficiency.
For evaluation purpose, the 4 pairs
of pressure and temperature gauges
installed at strategic locations (Figure
2) provide a good reference on
v

3. TECHNICAL
38 ASIAN FEED MAGAZINE – February/March 2016
steam management - clearly shows
how steam temperature responds
to pressure intervention at the PRV
(pressure reducing valve).
It is possible to generate all forms
of steam (super-heated steam,
moderate steam, and saturated
steam) from the same re-engineered
steam-piping set-up. This is useful
for countries, such as China and
Korea, with extreme and varying
climatic differences that dictates
compounded meal temperature.
As we need to work with different
steam temperature for different
meal temperature for countries
with extreme seasonal temperature
differences, this new approach in
steam piping engineering provides
flexibility for different steam type
options, which is very useful.
Depending on the meal temperature
(from a low of 5˚C to a high of 48˚C),
we are able to have total control on
the feed pelleting process.
Meal Temperature
Compounded meal after mixing
determines to a great extent, the
meal interaction with steam and
the relevant steam type to work
with. Very low meal temperature (in
cold countries in the cold months)
will better interact with super-
heated steam, whereas higher meal
temperature (38˚C and above in
warmer regions) requires saturated
steam to work with. The high meal
temperature in the tropics and during
summer months (ranging from 38–
45˚C) makes it difficult for steam
interaction with the meal during
conditioning. The use of deliquescent
salts has been shown to greatly assist
moisture adhesion to the meal.
Conditioning Temperature
Temperature setting at the
conditioner basically defines the
temperature space to work with for
different feed types and formulations
– the current industry norm is 75˚C
for swine feed, and 85˚C for broiler
feed. The current industry practice,
as a result of working with super-
heated steam (130 - 140˚C), usually
requires working with conditioning
temperature of 5 – 8˚C exceeding the
standard industry norm setting.
Increasing the temperature
setting technically provides for
more temperature space, hence,
signaling the flow control valve to
deliver that extra steam flow volume
to compensate for the shortfall in
available latent heat and moisture
from super-heated steam. Super-
heated steam does not have a fine
balance between temperature,
latent heat, and moisture. Revising
the traditional steam conditioning
process to now work with saturated
steam, provide a fine balance of
temperature (sensible heat), heat
(latent heat), and moisture. Saturated
steam provides more latent heat
and moisture, the two primary
prerequisites for cooking raw starch,
without the excessive temperature
(sensible heat). This will allow us
the flexibility to find an optimum
conditioning temperature of around
80˚C to work with for poultry feed,
which is sufficient to effectively
Figure 3: Thermal death time (TDT) curve for common microorganisms.
Note: 77˚C can effectively kill off the common pathogenic microorganisms in 1 sec. Steam with
sufficient amount of latent heat can certainly provide the element for the kill. This leaves us to
question the relevance of the hygienisers approach to feed sterilisation, at the expense of proper
steam conditioning.
cook raw starch, and also to better
preserve feed nutrient quality for the
best feeding value. It is important to
work with a conditioner with sufficient
residence time, to allow for proper
swelling of starch granule.
Pelleting may result in poor broiler
performance if the appropriate
temperature is not used during
conditioning. It has been shown
that high conditioning temperatures
are associated with poor broiler
performance, in terms of weight
gain, feed per gain and mortality.
Weight gain of birds fed diets steam-
pelleted twice was significantly lower
compared to those fed diets steam-
pelleted once. Feed intake of birds
fed twice steam-pelleted diets was
similar to those fed the mash diet,
while feed intake was higher in birds
fed once steam-pelleted diets. Getting
the job done first time without the
need to rerun fines a second time is
important.
Moderate thermal treatment of
feeds appears to improve their
nutritional value, which may be
attributed to improved starch
gelatinisation, increased enzyme
digestibility of protein, degradation
of heat-labile anti-nutrients, and
improving availability of nutrients and
feeding value of the feed formulation.
On the other hand, high
temperatures can destroy heat-labile
vitamins, enzymes and amino acids,
reduce the availability of starch by
formation of resistant starch and
lower the availability of lysine through
Maillard reaction. Furthermore,
increasing conditioning temperatures
above 80˚C can also increase the
viscosity of broiler diets based on
viscous grains (wheat, barley),
suggesting the release of previously
encapsulated NSP.
Residence Time
This is the passage time the meal
takes to go through the conditioner.
The objective of steam conditioning
is to fully plasticise the feed particles
and eliminate any dry core. This is
accomplished by performing three
core operations: heating, mixing
for proper infusion of steam with
the meal, and hydration for proper
swelling of starch granule and
leaching of starch matrixes. While
heating and moisture addition are
critical to pellet quality, good mixing
is needed to bring the surface of
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4. ASIAN FEED MAGAZINE – February/March 2016 39
Figure 4: Better-conditioned pellets (left) versus poorly conditioned pellets.
Note: both pellet feeds are of the same formula, produced from the same pellet mill with saturated
steam setting. The difference is in the chemistry of the deliquescent and surfactant and their
role and impact on starch cooking. A better cooked-feed has a noticeably darker color tone. This
trial was done with a conditioner, with just 22 seconds residence time, which is obviously grossly
insufficient.
the feed particles into contact with
the added steam. Longer residence
time in the conditioner also allows
moisture penetration (hydration) and
heat transfer to be more uniform.
It has been suggested that as the
hydration time of the feed particles is
much longer than the time required
to heat them, residence time of the
feed inside the conditioner should
be based on the time required for
adequate hydration, not the time for
adequate heating. This is where the
current engineering norm for steam
conditioners can be improved. We
need to work with saturated steam
at a temperature closer to saturation
point, with a long residence time of
60-70 seconds for maximum infusion
of steam into the meal, and allowing
for proper swelling of raw starch
granules.
Super-heated steam will provide
for adequate heating but there is no
adequate hydration; hence, the low
moisture uptake after conditioning.
Working with a higher conditioning
temperature can at best help to
get only a very marginal increase in
moisture from steam.
Saturated steam, with a delicate
balance of all the 3 elements
(temperature, heat, moisture)
provides for adequate hydration and
adequate heating. Saturated steam is
related to low pressure setting, and a
lower velocity steam flow entering the
conditioner.
The conditioner
Understanding the need to
cook raw starch, the conditioner is
definitely the most important element
of the feed pelleting process, and
an obvious tool to get the job done
effectively.
Important criteria for a good
conditioner:
• Have sufficient steam inlets –
allowing sufficient volume of low
pressure saturated steam entering the
conditioner
• Maximum fill ratio inside the
chamber – fully utilising the injected
steam for effective steam/mash
infusion
• Sufficient paddle shaft agitation
with minimum 60 seconds residence
time – for effective steam/mash
interaction.
Many conditioners in the market
cannot fulfill these important criteria.
Do take note that the long retention
of a hygieniser is just a slow screw
transporter and do not contribute
to any agitation, or proper steam/
mash interaction. The hygieniser has
not been engineered with much
consideration or priority to raw starch
cooking.
Relevance of pellet size to
starch gelatinisation
There is a relationship between die
hole diameter, starch gelatinisation
and pellet durability. Reducing the die
hole diameter (producing smaller size
pellets) can produce more gelatinised
starch and more durable pellets.
A higher degree of gelatinisation
in the outer portion of the pellet
compared to the whole pellet has
been reported. It is suggested that
heat and mechanical shear generated
next to the surface of the die hole
caused a substantial degree of the
gelatinisation. Therefore, it is plausible
that using dies with small diameter
holes enhances frictional forces
and provides more frictional heat
and gelatinisation to the core of the
pellet i.e. 3mm size pellet versus
4mm size pellets. However, the meal
must be appropriately conditioned
and sufficiently moistened, else
throughput capacity can be greatly
affected with smaller pellet size.
Pellet hardness
In a comparison of two different
pellet textures, namely, soft (1,662
g of pellet breaking force) and hard
(1,856 g of pellet breaking force),
broilers fed hard pellets had improved
nitrogen (N) and lysine retention,
true metabolisable energy – nitrogen
corrected, weight gain and feed
efficiency compared to those fed soft
pellets.
Conclusion
Proper steam conditioning is the
most important criteria of effective
feed pelleting. The conditioner is the
most important element of the feed
pelleting process. Get these wrong,
and everything goes wrong – from
feed processing efficiency, to the
feed quality, and livestock health/
performance.
The presence of deliquescent assits
moisture uptake from the condensing
steam, rapidly softening to swell the
raw starch granules. It is important
that the starch matrixes (especially
the amylose) leach out to be cooked.
This core objective underlines the
need to adopt the correct feed
processing technology and approach
for improved pellet feed quality and
feeding value. Nutrients not digested
by the animal, is nutrient wastage.
A combination of working with the
correct steam type in a given climatic
scenario, having deliquescent in the
mash meal to assist moisture uptake,
and working with a conditioner that
can provide sufficient residence time
for effective steam conditioning will
yield the best result. AF
*Steven Goh (steven@delstasia.com) is Executive
Director for Delst. A list of references is available
from the author.