Which factors influence the cleanability of dead-space-free mixing chambers in infant formula production?
The cleanability of dead-space-free mixing chambers is a central element of microbiological safety and product quality in the manufacture of infant formula. It rests on the interplay of hygienically compliant construction, surface quality, flow and process parameters during cleaning as well as a validated cleaning and hygiene strategy.
Hygienically compliant, dead-space-free construction
Freedom from dead space
"Dead-space-free" means a design in which no areas arise where product residues or cleaning media can stagnate or accumulate. This includes the consistent avoidance of crevices, undercuts, blind holes, unflooded dead legs, poorly flushed zones as well as sharp corners in the mixing chamber and on all product-contact internals.
Radii and transitions
Sharp edges and 90° corners encourage deposits and impede the flow of the cleaning medium. Hygienic internal radii (typically ≥ 3–6 mm) in vessels, pipes and fittings increase turbulence at the wall and the wall shear stress, so that particles and deposits are carried away better.
Connections and nozzles
Instrumentation connections (e.g. temperature, pressure or level probes) are to be executed flush-mounted and with a low L/D ratio (ideally L/D ≤ 1), in order to avoid "blind holes" and spray shadows. Welded-in nozzles and sight glasses should be integrated without dead spaces and with hygienic transitions.
Sealing systems
Seals represent potential weak points. They must close flush, positively and without crevice formation against the metal surface. Under pressure, elastomers must neither protrude into the product space (over-compression) nor recede (crevice formation). The choice of material (e.g. EPDM, PTFE) must ensure resistance to CIP/SIP media and thermal cycles, in order to maintain freedom from dead space over the entire service life.
Self-drainage (emptiability)
A mixing chamber counts as readily cleanable only if it is completely self-draining. A minimum gradient of approximately 1–3° and the avoidance of horizontal surfaces enable the complete drainage of product and cleaning media. The outlet valve is to be positioned at the lowest geometric point. Residual liquids promote not only dilution effects in subsequent batches but also microbial growth potential in standing water.
Surface quality and materials
Surface roughness
The mean roughness Ra is a key parameter for cleanability. In infant formula production, Ra values of ≤ 0.8 µm are customary, and Ra ≤ 0.4 µm is often aimed at by electropolishing. A low roughness reduces the adhesion of proteins, fats and mineral deposits and decreases the effective contact area for microorganisms, which facilitates the detachment of soiling during cleaning.
Surface treatment
Electropolished and homogeneously passivated surfaces minimise micro-roughness, micro-cracks and pitting. This not only improves cleanability but also impedes the formation and persistence of biofilms.
Choice of material
Austenitic stainless steels (e.g. 1.4404 / AISI 316L) are standard for product-contact components, since they are resistant to alkaline and acidic cleaning media as well as disinfectants. Corrosion (pitting, intergranular corrosion) creates "dead spaces" again at microscopic level and impedes sterilisation. Elastomers and plastics must be chemically resistant, thermally stable and compliant with the relevant food contact regulations (e.g. EU 1935/2004, FDA).
Flow conditions and cleaning mechanics
Turbulent flow and wall shear stress
During CIP cleaning, sufficiently high flow velocities and Reynolds numbers (typically above 4,000 in pipes) are required in order to achieve effective mechanical cleaning. High wall shear stresses detach deposits and prevent renewed deposition in boundary layers and edge zones.
Wetting and spray shadows
When cleaning vessels by means of spray balls or rotary nozzles, full-surface wetting has to be ensured. Agitators, baffles, guide plates, product probes or poorly positioned internals can cause spray shadows in which residues remain. The arrangement and geometry of all internals must therefore be chosen so that the cleaning media reach every surface.
Volume flow and residence time
Cleaning media are to be supplied at a defined volume flow, pressure, temperature and concentration and must act for long enough to detach soiling mechanically and chemically. The dead-space-free requirements also apply to CIP supply lines, return lines and valve nodes.
Process parameters of cleaning (TACT principle)
The effectiveness of cleaning follows the TACT principle (temperature, action, concentration, time):
Temperature
Typical temperatures in the alkaline phase (removal of protein, fat and biofilm) lie in the range of approximately 70–85 °C. Excessively high temperatures can lead to deposit formation (e.g. milk stone from calcium compounds), while excessively low temperatures impair the cleaning effect.
Action (mechanical effect)
The combination of flow velocity, impulse (spray jets, rotation), turbulence and possibly mechanical support (e.g. stirring movements during cleaning) ensures that deposits are detached and carried away.
Concentration
Defined concentrations of alkaline media (e.g. NaOH in the range of approximately 1–2 %) and acidic media (e.g. HNO₃ in the range of approximately 0.5–1 %) are used in order to remove organic and inorganic deposits. The concentration must be matched to the product characteristics, the degree of soiling and the resistance of the materials.
Time
Contact and action times are to be chosen so that complete cleaning is achieved without damaging the surfaces or sealing materials. Excessively short times lead to residual deposits, while excessively long times can encourage corrosion or material degradation.
Product-specific particularities in infant formula production
Soiling characteristics
Infant formula contains heat-sensitive proteins, fats, carbohydrates and minerals. Under unfavourable process conditions these can denature, caramelise or precipitate and form stubborn deposits. This calls for a coordinated cleaning regime that addresses both organic and mineral soiling without creating new deposits through precipitation.
Dry and wet areas
Infant formula is frequently present in powder form. In dry mixing chambers, moisture is particularly critical, since together with powder residues it creates ideal growth conditions for pathogens such as Cronobacter sakazakii and Salmonella. Dead-space-free constructions prevent moisture from being trapped in capillaries and areas that are difficult to access, and cleaning processes must ensure complete drying.
Allergen and cross-contamination management
Mixing chambers can be used for different formulations (e.g. different protein sources such as whey, soya and so on). Cleanability must be designed so that cross-contamination and allergen transfer can be reliably avoided through validated cleaning.
Validation, monitoring and documentation
Cleaning validation
Cleanability is demonstrated by methodical tests, for instance by riboflavin tests to check spray coverage and swab and rinse tests (e.g. ATP, TOC, conductivity, microbiological analyses) to check for residues. These tests serve to verify that no relevant product or detergent residues and no critical microbial counts remain.
Monitoring and hygiene management
A systematic hygiene concept (e.g. in accordance with GMP and HACCP) comprises formulation control, defined and controlled CIP cycles, regular microbiological checks as well as continuous monitoring of process parameters and plant condition.
Documentation
Complete and traceable documentation of the cleaning sequences, process parameters, releases and deviations is mandatory for infant formula. Only in this way can process reliability, traceability and regulatory conformity be ensured.
Regulatory and normative framework
The design of dead-space-free mixing chambers and their cleanability is guided by the relevant hygienic design guidelines and food law specifications, including:
- guidelines of the EHEDG (European Hygienic Engineering & Design Group)
- 3-A Sanitary Standards for hygienic process equipment
- FDA specifications (e.g. 21 CFR) and the Codex Alimentarius for infant formula
- European and national food hygiene and contact material regulations
The cleanability of dead-space-free mixing chambers in infant formula production thus results from a holistic hygienic design philosophy: only where construction, materials, surfaces, flow guidance, cleaning parameters and validation measures are consistently matched to one another can the reproducible level of cleanliness and safety required for infant formula be achieved.
How amixon® implements freedom from dead space and hygienic design
Freedom from dead space as a design principle
In amixon® precision mixers such as VM, HM, AM, KoneSlid® and SpherHelics®, the mixing chamber and mixing tool are welded free of crevices and ground smooth. There are no crevices, bolted connections or capillary gaps in the product-contact area, and the mixing tool is mounted and driven exclusively from above, so that the classically contamination-critical lower shaft passage is eliminated.
The standard connection with discharge flap closes flush and dead-space-free with the inner wall of the mixing chamber; dead-space-free ball segment valves are available as an alternative. The large inspection doors are manufactured by the Clever-Cut® process and seal permanently dead-space-free with the OmgaSeal® door seal, on request vacuum-tight or against overpressure.
Cleaning: wet and dry, validatable
Integrated washing lances enable wet cleaning of the mixing chamber; on request, amixon® supplies fully automatic wet cleaning. The SinConvex® mixing tool supports the complete drainage of product and cleaning medium. The mixers are designed for dry and wet cleaning regimes, so that changing between dry cleaning and wet cleaning is provided for.
The Clever-Cut® doors provide complete, ergonomic access to all product-contact surfaces and thereby form the basis for visual cleaning inspection as well as sampling within the scope of swab and rinse tests.
Certified standards
On request, amixon® mixers meet the EHEDG guidelines, the FDA hygiene guidelines, the design specifications of the 3-A Sanitary Standards and GMP requirements. VM and HM can be used FDA-compliantly as sterile mixers and reactors. The ComDisc® residual discharge – 99.997 per cent and better with free-flowing goods – minimises residues and cross-contamination risks when formulations are changed.
In dairy and infant formula production, amixon® mixers are in use worldwide at manufacturers and contract manufacturers: vitamins, minerals, trace elements, encapsulated omega-3 fatty acids and probiotics are mixed in homogeneously and gently downstream of the spray tower – without destroying agglomerates.
Manufacture in Paderborn as the quality foundation
amixon® develops and manufactures exclusively at the Paderborn works with the greatest depth of manufacture and all components from Germany. As a certified welding company with European, Japanese, Korean and American qualifications, amixon® designs every apparatus as a one-off on the basis of the operator's URS, and quality control remains entirely in-house without gaps. This manufacturing autonomy also secures long-term supply, since every component can be reproduced even decades later.
Verification in the amixon® pilot plant
amixon® checks in advance in the pilot plant, with 35 test units, whether the specific formulation delivers the expected results. Trials with the original product under real conditions are carried out, evaluated and documented jointly and serve as a robust basis for decision-making before the investment.