As part of the transition to circular agriculture and to reduce food-feed competition for arable land, the inclusion of coproducts in livestock feed is expected to increase. Pellet manufacturing allows for improving the handling properties of livestock feed, but the effect of fibrous coproducts on the process is poorly understood. Inclusion of coproducts is considered to affect the physicochemical characteristics of a feed mash, and subsequently pellet manufacturing. To understand how coproducts can effectively be incorporated in pellet manufacturing, we investigated the effect of the inclusion of 300 g/kg of various fibrous coproducts, differing in fibrous composition, in feed mash containing 700 g/kg of basic mash, containing soybean meal, maize and soy oil, on mash physicochemical properties and pellet manufacturing. Treatment mashes were prepared in singleton, steam-conditioned and compacted using a ring-die pelletizer. Physical pellet quality, production capacity, and energy consumption of the pellet press were evaluated per treatment mash. Mash physicochemical properties were evaluated by determining hydration properties (i.e. water binding capacity and sorption analyses) and thermomechanical properties (i.e. phase transition and capillary rheometric analysis). Pellet durability varied among treatments (15.8–91.1 %), as did total energy costs of compaction (28.0–38.7 kWh/tonne). Principal component analysis indicated that higher levels of insoluble fibre in a feed mash associated with increased shear stress during capillary rheometric analysis. Combinedly these parameters reduced production capacity (R2 = 0.25; P = 0.046) and increased required energy consumption by the pellet press (R2 = 0.30; P = 0.03), but could only limitedly explain variation among treatments. In conclusion, the inclusion of coproducts with higher or lower levels of fibre did not consistently affect physical pellet quality. The overall low pellet durability (<90%) of all treatments, however, illustrates the challenge for the pellet manufacturing of diets containing fibrous coproducts. In addition the effects on energy costs of production should be considered during feed formulation.

Pellet manufacturing allows for the improvement of the handling properties of biomass streams. Increasing channel length of the ring-die holes generally increases physical pellet quality. This phenomenon is often attributed to an increase in pressure gradient over the die and greater densification of the mash during compaction. It remains unknown, however, to what extent this improvement in physical pellet quality is attributable to the concomitant increase in die volumetric content, and, therefore, longer mean residence time (MRT) of the mash in the die. Here, we aimed to separate the effect of die geometry and MRT on physical pellet quality, by combining a pilot scale pellet manufacturing experiment with capillary rheometric analysis, for mashes containing different fibre-rich coproducts from food production. Net energy costs of compaction (in kWh t(-1)) were unaffected by production rate. Capillary rheometric analysis indicated that the work of friction between mash and the die hole wall did not increase at flow rates exceeding 1.0 mm(3) s(-1), suggesting the occurrence of plug flow behaviour. Hence, the work of friction generated between mash and the die hole wall depends on the friction coefficient between mash and the die hole wall and the total surface area of the ring-die. Increasing production rate decreased physical pellet quality (-2.56 to -0.93 kPa (kg s(-1))(-1)). Since the friction generated between mash and the die was unaffected by production rate, we conclude that this reduction in physical pellet quality is attributable to the concomitant reduction in MRT.

Black soldier fly larvae are considered an alternative source of protein due to their high protein content and low environmental impact of farming. The effect of incorporation of black soldier fly larvae protein (87.6 & PLUSMN; 2.4 g/ 100 g content) on meat analogues textural characteristics was determined and compared with those of meat analogues prepared with other alternative sources of protein such as soy protein isolate and vital wheat gluten, while beef round, chicken breast, and a commercial plant-based meat analogue were used as reference matrices. Textural characteristics of the experimental meat analogues were used as response variables in robust regression models (R2 > 0.96) built to determine the main effects and interactions of proteins. Black soldier fly larvae protein decreased the textural characteristics of meat analogues as its amount in the formulation increased. The interaction of black soldier fly larvae protein with soy protein affected the hardness and chewiness of meat analogues, whereas the interaction with wheat gluten only affected their cohesiveness. Black soldier fly larvae protein can partially replace traditional proteins in meat analogues. The optimal incorporations of black soldier fly larvae protein in meat analogues which mimics textural characteristics of chicken breast and plant-based meat analogues were 6.7 g/100 g and 21.5 g/100 g, respectively.

Due to the growing demand for food, the availability of starch-rich ingredients (e.g. feed grade cereals), whose areal can be used for producing food, is expect to decline. In turn, the use of co-products, from food -and biofuel industry, is expected to increase in livestock feed. However, these co-products are fibre-rich and can negatively affect pellet manufacturing, by reducing pellet quality and increasing energy costs. The thermomechanical properties of feed mashes are considered to be important for agglomeration pro-cesses, but its relation to feed composition and its role in pellet manufacturing is poorly understood. The aim of this study was to investigate the effect of fibrous co-product inclusion in feed mashes on their thermomechanical properties and subsequent effects on pellet manufacturing. Treatment mashes were formulated to contain 700 g/kg basic mash, consisting of soybean meal, maize, and soy oil, to which 0-300 g/kg palm kernel expeller, sugar beet pulp, wheat straw and isolated native maize starch were added, according to a four-component mixture design. Treatments were prepared in duplicate, conditioned using a single-shaft conditioner and compacted using a ring-die pelletizer (die hole diameter 6 mm, L/D ratio 12). Pellet quality, production capacity and gross specific mechanical energy consumption per megagram (Mg) were documented. Mash deformability was evaluated by increasing the moisture content of a mash sample to 150 g/kg, followed by compression at 10 MPa and increasing temperature by 4 degrees C/ minute using the Phase Transition Analyzer (PTA; Wenger Manufacturing, Sabetha, KS, US). Inclusion of wheat straw significantly increased mash deformability. Inclusion of isolated native maize starch and fibrous co-products was observed to increase pellet quality in comparison to the basic mash. Mash deformability at compactor temperature was correlated with bulk density (r =-0,83; P < 0.001). Pellet compressive strength was associated with mash deformability (r = 0.78; P < 0.001), but this association was observed to be influenced by wheat straw. Material deformability was correlated with production capacity (r =-0.85; P < 0.001) and energy consumption (r = 0.80; P < 0.001). In conclusion, inclusion of fibrous co-products affects pellet quality in a non-linear relation and increases pellet quality similar to inclusion of isolated native maize starch. Mash deformability could provide an indicator for pellet quality, but the underlying mechanism requires further study. Pelleting of feed mashes with a higher deformability increases energy costs of pellet manufacturing, due to the behaviour during compaction. The thermo-mechanical properties of feed mashes play a significant role in the pellet manufacturing process.

Pellet manufacturing is a useful tool for improving the handling of livestock feed. Pellet manufacturing consists, among others, of a compaction step, which is strongly affected by feed formulation. The role of feed formulation is thought to result from the fact that feed mash physicochemical properties change depending on ingredient composition. This variation in physicochemical properties subsequently affects mash behaviour during compaction, leading to variation in both physical pellet quality and energy costs during pellet manufacturing. Methodologies that allow for the study of material behaviour at pellet manufacturing conditions are needed to investigate the effect of feed formulation on mash flow behaviour. Such methodologies, however, are currently not generally available in the field of feed manufacturing. In this short communication we aim to discuss the application of capillary rheometry as a potential method for studying feed behaviour in the die, at conditions comparable to those during pellet manufacturing. The similarity between the design of the capillary rheometer and the geometry of a ring-die compactor allows for the simulation of some of the conditions experienced by feed mash during compaction, using smaller quantities of sample materials. The observed relation between flux and pressure gradient, for feed mashes evaluated in this short communication, resembles a Herschel-Bulkley relation, indicating that the increase in pressure gradient depends non-linearly on flow rate. While individual pressure gradients provide insight in the relative energy costs of compaction, a modelling approach is recommended to simulate the behaviour of feed mash at conditions more closely approximating those during pellet manufacturing. In summary, capillary rheometry provides an option for studying feed mash behaviour at conditions approximating those in the pellet press during pellet manufacturing.

This study investigated the functional properties and essential amino acid composition of proteins extracted from black soldier fly larvae which represent a good source of proteins (30.12% dry matter). The proteins extracted in alkaline conditions (pH 11) were then isolated using two different recovery methods, (i) ultrafiltration, and (ii) isoelectric precipitation. Ultrafiltration provided higher purity of proteins (96.42%) but a lower extraction yield (24.30%) compared to isoelectric precipitation which provided a protein purity of 76.02% and higher extraction yield (37.22%). All essential amino acids were present in adequate quantities for human requirements. The fraction of proteins obtained by ultrafiltration had significantly higher oil holding capacity and foaming capacity than isoelectrically precipitated proteins. The protein fractions obtained by ultrafiltration and isoelectric precipitation had oil holding capacity of 125.8% and 81.6%, while the foaming capacity was 141.9% and 114.3%, respectively. These technological functionalities can be used to improve human food characteristics, thus resulting in enhanced consumer acceptance. Industrial relevance: The food industry seeks alternative and sustainable sources of proteins, such as insect proteins, to reduce the environmental impact (i.e., greenhouse gas emissions). Consumers' acceptance is the main barrier to adopting edible insects in commercial applications. The acceptance increases when the insect proteins are incorporated in food products as ingredients rather than consuming the whole insect. Hence, this study focuses not only on extraction of proteins but also on functional properties of those proteins making it easier to target specific food formulations (i.e., whipped toppings), which require specific functionalities (i.e., foaming capacity and stability). The protein purity was increased by including an ultrafiltration step. The proteins obtained through the ultrafiltration method showed better oil holding capacity and foaming stability compared to proteins obtained by isoelectric precipitation. The strategies assessed in the present study help enhance the purity of larval proteins and improve their functional properties, thereby opening up new opportunities to incorporate this ingredient into targeted food formulations and improve consumer acceptance.

Freshwater crayfish have the attention of watermanagers in The Netherlands because of their burrowing activity and negative impact on aquatic ecosystems. As a result, several attempts are being undertaken to remove the crayfish. However, no attention is given to the follow-up step in this process: i.e. what to do with all those crayfish? This investigation will focuss on the potential use of freshwater crayfish in animal feed. This will be based on crayfish nutrient and energy composition, the requirements of specific feeds and the intervention costs (i.e. the costs under which it becomes economically viable to incorporate crayfish in feed).

The objective of the present study was to investigate whether mixing ratio of maize and soybean meal (SBM) affects the breaking behaviour during hammer-milling in terms of the nutrient properties and in vitro digestibility of fractionated particles. Mixtures of maize and SBM with different proportions (% Maize:SBM; 0:100, 25:75, 50:50, 75:25, 100:0) were hammer milled using a 2-mm screen. The obtained powder was sieved into seven fractions with size ranges from 0.149 to 1.190 mm. Results show that energy consumption of grinding mixtures increased from 3.8 to 48.4 kJ/kg with the maize proportion increasing from zero to 100%. Mixing proportion of maize and SBM showed significant effects on nutrient content of fractionated material. For hammer milled material < 595 mu m, the in vitro digestibility of crude protein (CP) and organic matter (OM) of fractionated material decreased with increasing particle size. Additionally grinding fractionated particles >= 595 mu m over a 1-mm sized screen before in vitro digestion analysis increased the digestibility of OM and CP. Equivalent particle size (EPS) and geometric standard deviation (GSD) of hammer milled maize and SBM and their mixtures correlated better than geometric mean diameter (GMD) to OM and CP in vitro digestibility in a linear regression model. In summary, the mixing ratio of maize and SBM had a significant effect on the breaking behaviour of ingredients and in vitro digestibility of CP and OM of the isolated fractions. Mixing ingredients before grinding is suggested in terms of saving energy consumption. The GSD/EPS of ground material should be considered while studying the effects of particle size distribution on the in vitro digestibility of nutrients. (C) 2022 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan.

Particle size plays an important role in the digestibility of nutrients by animals. Methodologies developed to simulate the digestive system to determine digestibility values require the grinding of samples to pass a specific sieve size (e.g. 1 mm) before in vitro digestion. The objective of this study was to evaluate if particle size affects in vitro (ileal) digestibility values of organic matter (OM) and crude protein (CP) in maize and soybean meal (SBM). Both ingredients were ground in a laboratory mill over four screens (1.50, 1.00, 0.75 and 0.50 mm) with trapezoidal holes in a sequential manner from large to fine. Particle size distribution, nutrient content and in vitro digestibility were determined of the various samples. With decreasing screen size, geometric mean diameter of particles significantly decreased from 351.4 to 203.2 µm for maize, and from 239.1 to 99.1 µm for SBM. Ash, CP and starch content were not affected whereas the neutral detergent fibre in maize and dry matter content in SBM differed after grinding with various sized screens (P < 0.05). The in vitro digestibility of OM and CP of maize and CP of SBM ground over the four different screens did not differ (P > 0.185). The OM in vitro digestibility differed (P < 0.05) with values for SBM ground over the 1.50 mm screen being lower (P < 0.05) than the smaller screen sizes: 0.814 (1.50 mm) vs 0.833 (1.00 mm), 0.829 (0.75 mm) and 0.834 (0.50 mm), respectively. Based on the current work and literature data, particles ≥ 595 µm of comminuted maize and SBM affect OM and CP in vitro digestibility. Analysis of three feeds and 10 feed ingredients ground over a 1.0 mm sieve showed that the fraction ≥ 595 µm can make up to 32.1% of the mass. It is recommended that before in vitro digestibility determination, particle size distribution is assessed, especially the mass fraction of particles ≥ 595 µm and further grinding is conducted to ensure that particles are < 595 µm for maize and SBM. The cut off size where particles size affects OM and CP in vitro (ileal) digestibility of other feeds or feed ingredients than maize and SBM should be determined.

Grinding is an important feed processing technology, determining physical and nutritional characteristics of ground materials, which affects nutrient digestion in animals and their growth performance. This study aimed to clarify if differences in moisture content (MC) lead to differences in nutrient composition over various particle size fractions after grinding that have potential to affect feed manufacturing characteristics or animal performance. Maize and soybean meal (SBM) with targeted MC of 120, 140 and 160 g/kg (adding no (0), 30 and 60 g/kg of tap water, respectively) were hammer-milled and the physical and chemical characteristics as well as in vitro apparent ileal digestibility (AID) of particle size fractions were determined. The mill was fitted with a 6-mm (maize) or 2-mm (SBM) sized screen, with milled material subsequently separated by dry sieving (size ranging from < 0.075 to > 3.36 mm) and each fraction was analyzed for its nutrient composition, morphology characteristics and in vitro AID of organic matter (OM) and crude protein (CP). For the latter assay, specific particle size fractions were additionally ground using a laboratory mill (1 mm screen). Geometric mean particle size diameter and energy consumption increased with increasing MC (P < 0.05). Chemical composition, physical characteristics and in vitro AID of particle size fractions were significantly different (P < 0.001). Moisture addition had no significant effect on nutritional and physical parameters except for solidity in maize, ash content, projected area, circularity, and solidity in SBM. Physical characteristics of particles, especially particle size affected in vitro AID of OM and CP most (P < 0.05). Additional grinding of samples before determination of in vitro AID increased the OM digestibility up to 0.684 in maize (P < 0.001). Additional grinding of particles larger than 0.595 mm increased in vitro AID of OM and CP (P < 0.05). In summary, increasing MC has limited effect on the breakage behavior of maize and SBM, but increased energy consumption during hammer-milling. In vitro AID measurement of fractionated particles appears to require material should be ground to pass a 0.595 mm sieve rather than the prescribed 1 mm.

In 2019, a report was issued by Buijs en Samwel-Mantingh which claimed a possible relation between the occurrence of pesticides and veterinary drugs in manure and the decline of farmland birds, which feed on (soil) invertebrates allegedly impacted by these substances. The current research project provides an in-depth analysis of the reliability of the measured concentrations, an analysis of the potential risk to (soil) invertebrates of single compounds and mixtures and an assessment of potential pathways of these substances into the manure.

Feed technology involves the processing of ingredients and the manufacture of animal feeds and is an integral part of animal production systems to provide high quality and nutritious food. The objective is to transform low quality ingredients into higher value feed components, and improve nutrient utilization of compound feeds. Animal feed, therefore, has a social responsibility to contribute to more sustainable food production systems. Further understanding of the structures and functional properties of feed components, their changes with different primary and secondary processing and their conditions, are essential to more accurately meet nutrient requirements of animals. In addition, it will enable a more accurate assessment of overall costs of processing or production with respect to the societal responsibility of feed processing; this may include energy use, carbon footprint, use of water resources and life cycle assessment. Accurate and fast testing technologies should account for the variability within ingredients and the different practices used in the equipment and raw material processing, as well as those in feed mills. Big data will play a pivotal role to model specific aspects of feed manufacturing and could enable the development of a model integrating characteristics of diet ingredients, recipe and processing conditions, whilst optimizing energy consumption, (physical) feed quality and production rate. Collaboration between skilled data scientists, machine experts, feed manufacturing technologists and nutritionists, using advanced data analytics is, therefore, required for future process optimisation. An improved interaction between those responsible for the actual formulation of animal diets, feed technologists and mill operators may result in a more constant final feed product quality and the lowest electrical and fossil energy consumption during manufacture, despite inclusion of alternative/substitute ingredients. Lesser known, novel processing techniques may significantly contribute to improve the nutritional value of raw materials and complete feeds. However, only a few techniques may be scalable to economically feasible processes, while others may only be applicable to one animal species and not usable as a general process. In addition, modern feed mills need flexibility and the ability to switch to serve customer wishes and logistics where feed recipes and feed forms are concerned. A major constraint to conduct research in feed processing is the difficulty to acquire attention and funding. More attention should be given to feed additives in processed feed (mainly in pellet form), with research focused on the interaction effects between feed processing conditions, feed components and feed additives. Finally, future feed technologists will require recognized qualifications, possibly to a diploma level. Courses must be successfully completed and include knowledge on smart manufacturing and integrated process control systems. From a feed industry perspective, success of participation in the next industrial feed mill development will be determined by how well staff are prepared and trained.

Particle size of diets or ingredients plays an important role in pig growth and gut health. The way the size of particles is measured and expressed, however, is limited in explaining pig growth performance differences. This review explores new possibilities to determine, express and predict particle size. Different grinding methods, including the use of roller mills, hammer mills, multicracker and multi-stage grinding were reviewed. Roller milling tends to produce a more uniform particle size distribution (PSD) and consumes less energy, whilst hammer mills have a greater grinding capacity and a higher reduction ratio compared to roller mill. The multicracker system, a more recently developed technology, can be considered cost-effective and ensures grinding capacity. Since the effects of different grinding methods vary, multi-stage grinding, combining different grinding methods, might be a solution to obtain a defined PSD. Particle size determination techniques, including dry/wet sieving, laser diffraction, microscopy, and static/ dynamic image analysis are described and compared. It is concluded that more characteristics of particles (e.g. shape, volume or surface area) should be investigated. Besides geometric mean diameter (GMD), particle size can also be expressed with parameters such as D-50, D-4,D-3 and span of PSD. Equivalent particle size (EPS) is introduced as a mean of describing the size of particles related to a functional trait of the particles. A meta-analysis was performed by collecting particle size and pig performance data from scientific studies examining the effect of recalculated EPS on pig performance (feed conversion ratio, FCR). Regression/linear modelling shows that recalculated EPS was not better than GMD in explaining pig performance differences due to the high variation among studies. Different expressions of PSD may result in different conclusions. An introduction of describing the breaking behavior of diet ingredients via mathematical models is provided. The development in breakage functions of wheat in roller milling in food preparations indicates that breakage functions are applicable in predicting the output PSD. Functions may also be extended to diet ingredients to be ground in animal feed manufacture. In feed manufacturing diagrams, particle size reduction for downstream processes (e.g. pelleting, extruding, expander processing) should be taken into account when the relationship between pig performance and particle size of diets is investigated. In conclusion, the determination, expression and prediction of particle size can be a new direction for controlling the grinding process in the feed mill to better explain its relationship with pig performance.

This paper discusses some more fundamental properties associated with the physical quality of pelleted animal feed. The focus is on concepts used in chemistry, physics and soft matter research to discuss the impact of time on heat and water diffusion into particles in the conditioning/pelleting process. It is argued that the extent of transformation of feed components as for instance starch is limited by the availability of water and that the distribution of water in the feed mash particle is governed by particle size, water diffusivity and the time available for hydration in the conditioning process. The role of the glass transition in altering the apparent viscosity of the feed mash resulting in a change of the compaction characteristics of the feed mash is discussed. Bond types in feed agglomerates consist of capillary forces during the compaction phase (pelleting) and transform to solid types of bonds during cooling. Overall, time dependent processes as indicated above give rise to observed differences in the final physical pellet quality and observed systems parameters in feed manufacturing.

This research investigated three grinding technologies to reduce the size of maize, wheat and full fat soybeans to a course particle. To correct for the different mechanisms of particle size reduction between the different mills, the relationship between specific mechanical energy (SME) and its resulting mean particle size was expressed per ton of ground product. Analysis of co-variance was used to estimate differences between the treatment means after correction for energy consumption. Experimental results, obtained under pilot scale grinding tests, showed that type and conditions used for the three mill types affected size reduction ratios for maize, soybeans and wheat. The RR of particles was smallest for the roller mill and multicracker device and largest for the hammer mill for all feed materials studied and varied between 1.60 (roller mill, wheat) and 5.95 (hammer mill, maize). The mean particle size was smallest when grinding using a hammer mill with a 5 mm screen. The efficiency of energy use was calculated as effective SME (kJ/kg). Total energy use was shown to be the highest for the hammer mill. Soybeans required the largest amount of energy for grinding, with maize the smallest. The constant for Kick's law (C-k values, kJ/kg) per grinding device was calculated to relate particle sizes and energy demand: both roller mill and multi cracker device showed lower C-k values, indicating a better grinding efficiency of these devices. For coarse grinding, the roller mill was shown to be the most energy efficient device followed by the multicracker device and the hammer mill was the least efficient. For feed manufacturers it is important to use/combine these devices to ensure an efficient milling operation and to match the grinding device with its specific grinding objective (fine, coarse or with a specific particle size distribution). Tasks are different per animal species and were discussed.

Insects provide a very promising alternative for the future production of animal protein. Their nutritional value in conjunction with their food conversion efficiency and low water requirements make them a more sustainable choice for the production of food of animal origin. However, to realize their potential as a viable source of food for a growing human population, it is necessary to create the infrastructure for their production, processing, storage, distribution, and marketing, and to develop legislation for their use as food. But none of these steps become relevant unless we have the ability to produce insects in sufficient quantities to supply the potential demands for animal protein. In this chapter we present and describe the current technologies and state-of-the-art of insect production (farming) for feed and food. Nutritional requirements of insects are discussed with methods for developing and producing insect feed formulations. An example of a modern insect farm is presented describing mechanized and automated steps on multiple insect species production. Current methods for producing the yellow mealworm (Tenebrio molitor L.), the super worm (Zophobas morio Fab.), the housefly (Musca domestica L.), the soldier fly [Hermetia illucens (L.)], the house cricket (Acheta domesticus L.), and the greater wax moth (Galleria mellonella L.) are described in detail. And an extensive review of the equipment currently available for environmental rearing room control and process automation is presented and discussed.

The effects of changes in process parameters and their effect on pellet quality in terms of hardness and durability are discussed, The pelleting process in this respect is the combination of conditioning, pelleting and cooling. The parameters discussed with respect to the conditioning process are process variables such as steam and water and system parameters such as residence time and pressure.Parameters during the pelleting process that can be adjusted or influence pelleting properties of a feed mash include layout (e.g. flat-bed vs. ring-die pellet press) and dimensions, roller and die assembly and die velocity of the pellet press, The effect of the changes in one or more parameters and its effect on pellet quality (durability and hardness) is however often a matter of the judgement and experience of the operator. For instance, a certain increase in the amount of steam added to a feed mash generally improves pellet hardness and durability. Increasing the amount of dissipated power in the feed mash, generally has a similar favourable effect on pellet quality. The extent to which pellet hardness and durability rise is however dependent on feed formulation and other parameters as temperature of the feed mash and cooling air characteristics. The latter parameters can be measured but their relation to the pelleting process is often not clear.Pellet quality, as affected by cooling, is mainly determined by the bed-height of the pellets in the cooler, pellet-size, air-flow and air-characteristics during the cooling period.The use of modern conditioning systems to operate at a wide range of processing and system variables means that pellet quality is dictated more by equipment than by diet formulation.However, use of such conditioning systems must always be justifiable in terms of cost and pellet quality, rather than the dictates of fashion.It is concluded that the amount of steam is a more decisive factor than steam pressure. In addition, it seems that the individual steam supply of a factory has a larger influence on the measured pellet hardness and durability than would be expected from theoretical relationships concerning steam in an ideal situation. Although water has binding properties as well, it is concluded that steam is far superior to water in producing good quality pellets. The additional heat included in the meal permits changes in physico-chemical properties which lead to more durable and hard pellets. Equipment which incorporates some form of hold-time enhances the possibility to incorporate more liquids, without detrimental effects on pellet quality. The use of pressure to alter physico-chemical properties of the feed in combination with water and heat, and the use of pressure to pre-densify the feed mash prior to pelleting seems to be important in obtaining a good quality pellet.Pelleting is not the sum of conditioning, pelleting and cooling steps, but should be considered as an integral system which performance is dependent on interrelations between the three unit operations: conditioning, pelleting and cooling. However, these interrelations with respect to the different formulations used, are still poorly understood. The use of decision support systems and process optimization procedures may nowadays greatly enhance the opportunity to obtain the best possible quality of pelleted feeds with minimal use of labour and energy for a given feed formulation.

In a series of three articles, the physical quality of pelleted animal feeds is discussed from an engineer's point of view. In this first manuscript an overview is given on the binding mechanisms in pelleted animal feeds. Principles and methods for evaluation of physical quality of pelleted animal feeds are reviewed with respect to pellet hardness and durability. Methods are outlined with respect to quality standards both from a pragmatical and scientific point of view.It is concluded that binding in pellets most probably is due to solubilisation and subsequent crystallisation of feedstuff components e.g. starch, sugars, fats or 'liquid necking', Liquid necking is a binding mechanism which uses the surface tension of water, in a three-phase system of air, water and particles to maintain structural integrity of the pellet. Soluble components might be introduced in the feed mash subjected to pelleting, They are either incorporated in the mixing phase or result from processing as a function of processing variables during the subsequent stages, conditioning, pelleting and cooling/drying, of the feed manufacturing process. To evaluate the physical quality of pelleted feeds, generally a subdivision is made into tests that evaluate 'hardness' and tests evaluating 'durability' of a given pellet. Several devices measuring fragmentation strength, and devices determining abrasion strength of pellets are discussed. It is concluded that some tests presently available evaluate a mixture of hardness (fragmentation) and durability (abrasion) effects, The feed manufacturer or feed technologist should be aware of the reason for evaluating the pellet quality and subsequently choose the appropriate, most suitable method, since no unique test exists that covers all parameters of interest related to physical quality of pelleted animal feeds.