Which parameters determine the reproducibility of mixing processes in food ingredients manufacturing?
The reproducibility of mixing processes with powdered materials describes the ability to achieve a comparable homogeneity and product quality across many batches under the same conditions. It depends above all on the properties of the powders, the process management, the plant technology and quality control.
1. Material- and substance-specific parameters
Particle size distribution (PSD): differing grain sizes encourage segregation, particularly with free-flowing powders.
Bulk and tapped density: they influence flow behaviour, compaction and dosing accuracy.
Moisture content and water activity: they govern cohesion, the tendency to agglomerate and flowability; hygroscopic powders react particularly sensitively to fluctuations.
Flow properties: characteristic values such as the Hausner ratio, Carr index or flowability under load describe conveyability and mixability.
Electrostatic behaviour: it can lead to build-up, lump formation and uneven distribution of fine constituents.
Particle shape and surface condition: shape, roughness and surface moisture influence friction, contact behaviour and the movement of the particles within the mixer.
2. Procedural and process-related parameters
Mixing time: it must be defined and kept constant; times that are too short lead to inhomogeneity, times that are too long can encourage segregation.
Rotational speed, circumferential speed and energy input: these variables determine the mixing intensity and must be run stably.
Fill level of the mixer: it influences particle movement and flow patterns. Deviations can change the mixing quality considerably.
Order of addition: with micro-components in particular, the defined order of addition is decisive for an even distribution.
Temperature and moisture management: they influence flow behaviour, agglomeration and possible changes to the powder properties.
3. Plant- and equipment-specific parameters
Mixer design and mixing mechanism: convective, diffusive or shearing systems generate different mixing regimes.
Geometry and arrangement of the mixing elements: wall clearances, shape and position of the tools determine flow and shear fields.
Condition of mixing tools and internal surfaces: wear, deposits or changes in tolerance alter the process conditions.
Discharge behaviour and dead spaces: residual quantities can influence subsequent batches and impair reproducibility.
Dosing accuracy of upstream systems: fluctuations in dosing act directly on the achievable homogeneity.
4. Measurement, control and quality parameters
Process validation and statistical evaluation: mixing quality is frequently described via the coefficient of variation.
Inline and at-line analytics: spectroscopic methods or image processing enable monitoring of homogeneity.
Sampling strategy: the number, location and timing of samples must be standardised, since they strongly influence the assessment of mixing quality.
PAT (process analytical technology): supports the ongoing monitoring and control of critical process parameters.
5. Ambient conditions
Room temperature and relative humidity: they influence moisture uptake, flow behaviour and agglomeration.
Air movement and pressure conditions: they can influence dust behaviour and particle dynamics, above all in open processes or pneumatic conveying.
How amixon® safeguards the reproducibility of mixing processes
Representative sampling is the foundation
Every meaningful assessment of mixing quality (RSD, CV) begins with the homogeneity of the raw materials used. Natural ingredients in particular are subject to fluctuations which can be caused, for example, by the time of harvest, the origin, the freshness, the storage conditions or weather influences. With the Gyraton® silo mixer, amixon® stabilises this variability as early as raw material intake: large batches of up to approximately 100 m³ are homogenised with very low energy demand and form a reproducible starting basis for the subsequent mixing processes. Precise dosing scales above the batch or process mixer additionally secure the exact weighing of the individual components. The dead-space-free operation and almost complete discharge of amixon® batch mixers ensure high batch fidelity and minimise the risk of cross-contamination.
In the pilot plant, amixon® works out a sampling regime together with the operator which is both statistically robust and largely automatable and which can later be transferred into production operation.
A stable process basis instead of subsequent correction
amixon® mixers generate a technically ideal random mixture independently of the fill level, within the range of approximately 10 to 100 %. A once-validated combination of parameters comprising mixing time, circumferential speed and fill level window always leads to the same mixing quality. The most effective inline monitoring therefore consists in the consistent control of these process parameters. The mixing programs are stored in the control system, so that deviations from the target time or target rotational frequency become immediately visible and can be corrected with process reliability.
Documentation is seamless and GMP-compliant
For regulated areas, the integration of the mixing processes into the operator's higher-level ERP system is advisable, including defined cleaning programs. Depending on the industry, product group and degree of soiling, different cleaning regimes are used: from visual inspection of the residual discharge through cleaning with dry and damp cloths to manual and automatic wet cleaning. In the wet cleaning variants, the complete, validatable drying of the mixing chamber is of particular importance.
amixon® supports operators in shaping these procedures in a GMP-compliant manner. On request, the necessary documents for DQ, IQ and OQ are provided. amixon® prepares the documentation for its own apparatus; on request it follows EU GMP and FDA 21 CFR Part 11 and thereby forms a robust basis for audits and inspections by the authorities.
Pilot-plant trials to minimise risk
Fluctuating analytical values, visible segregation at the discharge or batch-dependent product properties are as a rule indications of sampling errors, segregation after the mixer or unsuitable parameter settings. At amixon®, such effects are not left to everyday production but are systematically investigated and remedied in the pilot plant with the original product, before they lead to scrap, complaints or additional costs.
In the manufacture of food ingredients in particular, amixon® combines ideal mixing qualities with hygienic design in accordance with EHEDG, FDA and 3-A, microfine liquid incorporation and almost complete discharge. A reproducible quality is thereby ensured even with frequent recipe changes and demanding declaration requirements.
Product protection as a constructional system property
amixon® mixers deliberately operate at low speed: the circumferential speed of the tools typically lies between approximately 0.8 and 3.5 m/s. Mixing is performed by means of SinConcave® and SinConvex® helical mixing tools which convey the product upwards at the periphery and downwards in the centre following gravity. This creates three-dimensional flows without pronounced throw, impact or crushing zones and without measurable heat input. Sensitive structures, coatings and agglomerates are preserved. Where targeted deagglomeration is required, switchable cutting rotors are used which act locally without permanently subjecting the entire batch to high shear energy. Because the entire amixon® mixer range is based on helical mixing tools running at low rotational frequencies, all series operate gently on the product – provided that no cutting rotors, high-shear blades or rotor-stator systems are switched on.
Hygienic design as the basis for mixing quality and cleanability
All the properties named build on the amixon® hygienic design: the mixing chamber and mixing tool are welded free of joints and hygienically ground. The mixing tool is supported exclusively at the top, so that a contamination-critical lower shaft passage is eliminated altogether. Generous Clever-Cut® inspection doors with permanently dead-space-free OmgaSeal® sealing enable ergonomic access to all product-contact surfaces. Dead-space-free discharge fittings and programmable washing lances enable validatable dry and wet cleaning in accordance with the EHEDG guidelines, the FDA hygiene requirements and the 3-A Sanitary Standards.