A continuous detergent mixing process with liquid addition is controlled stably when a gravimetric main stream forms the reference variable and all solid and liquid streams are tracked via fixed, monitored recipe ratios. The liquid should be added via a fast, mass-flow-controlled dosing loop; a superordinate ratio controller couples its setpoint to the actual solids throughput.

Cleanability with cocoa, fat and other sticky powder recipes starts with a hygienic, accessible and, as far as possible, fully dischargeable design. Smooth, flush surfaces, minimised deposit points, readily accessible seals, suitable inspection openings and a fully drainable design are key prerequisites.

Mixing quality and particle integrity can be ensured simultaneously when the mixing process is matched to the granulate's breaking strength. For sensitive press granulates, gentle mixing principles such as container, tumble, V, double-cone or cone-screw mixers are especially suitable. Slow-running convective mixing systems can also be suitable, provided speed, fill level, mixing time and feed conditions do not overly stress the particles.

Viscous binders can most reliably be dosed via a temperature-controlled, as short as possible positive-displacement pump–line–nozzle chain. Low-dead-space valves, self-draining piping, suitable atomisation and a validatable cleaning design are more important than any single component. The design must jointly consider the binder, viscosity, temperature, dosing quantity, product movement and hygiene requirements.

For the combination of mixing, liquid addition and granulation, high-shear mixer-granulators, fluid-bed plants, continuous twin-screw granulators and certain mechanically fluidised mixers are especially suitable. High-shear systems often produce compact granulates, fluid beds can combine granulating and drying, and twin screws are suitable for continuous processes. The right choice depends on the desired granulate structure, product behaviour, liquid addition, cleaning, safety and trial verification with the original product.

For continuous detergent processes with liquid additives, ring-layer mixers or ring-layer granulators, ploughshare mixers and twin-shaft paddle mixers are especially suitable. Ring-layer systems are suitable when intensive wetting or agglomeration is desired. Ploughshare mixers offer a flexible solution for the continuous wetting of powders. Twin-shaft paddle mixers are advantageous when a uniform and, at the same time, gentle incorporation of sensitive granulates or additives is required.

There is no universally optimal mixer for incorporating flavours, prebiotics, vitamins and trace elements into milk powder. Twin-shaft paddle mixers, ploughshare mixers and, in particular, vertical twin-shaft mixers are suitable solutions when short mixing times, high homogeneity and, where applicable, controlled addition of liquid flavours are required. For particularly sensitive, agglomerated milk powders, cone-screw or container free-fall mixers can be advantageous when predominantly dry components are processed.

For slips and low- to medium-viscosity ceramic suspensions, rotor-stator mixers are suitable for rapid wetting and breaking up soft agglomerates. Where a finer and more stable dispersion is required, stirred bead mills, pearl mills or attritors are usually the more effective solution. Grinding-media abrasion, temperature rise and possible changes to the primary particles must be taken into account.

A defined particle-size distribution is controlled above all by the liquid-to-solid ratio, the properties and distribution of the binder, droplet size and spray rate, mechanical energy input, residence time, and temperature and drying conditions. The liquid-to-solid ratio is often the dominant control variable in wet agglomeration: too little liquid favours fines and weak agglomerates; too much liquid promotes oversize particles, lump formation and broad distributions.