Caking of micronized dry-fractionated plant protein powder arises mainly from high specific surface area, moisture sorption, inter-particle cohesive forces, static charge and mechanical compaction. Prevention covers raw material, process, handling and packaging controls.
Strictly control moisture and relative humidity
This is the most critical factor. Ultra-fine protein particles readily absorb water vapour. Even minor moisture creates liquid bridges between particles and triggers caking.
Maintain powder outlet moisture at a stable low level (typically 6–9% for legume protein). Avoid over-drying which increases static and dust risk.
Keep milling, classification, conveying and filling zones at low relative humidity (RH <45%). Use dehumidified air in the production hall.
Prevent cold powder contacting warm humid ambient air, which causes surface condensation.
Optimize grinding fineness and particle size distribution
Avoid unnecessary over-micronization. Excessively fine particles drastically raise van der Waals attraction and agglomeration tendency.
Set a defined PSD target and stop grinding once protein bodies are sufficiently liberated. Do not pursue finer size than application requires.
Control broad PSD: excessive fine fractions filling void spaces between larger particles increases compaction risk.
Reduce static electricity
Ultra-fine protein powder builds static charge during pneumatic transfer. Charged particles cling together and form soft agglomerates that may harden into cakes under pressure.
Earth all mill, classifier, pipeline and hopper components; use conductive liners and antistatic filters.
Add small amounts of dry antistatic food-grade additives if formulation permits.
Use properly conditioned process air to reduce static build-up.
Minimize compaction during storage and transport
Static pressure from stacking bags or bins compresses fine powder and strengthens interparticle contacts.
Use mass-flow hoppers with low-friction liners; avoid long powder residence time inside intermediate bins.
Limit bag stacking height. Use low-weight packaging containers where possible.
Apply gentle vibration only for feeding, avoid continuous vibration during storage.
Food-grade anticaking agents / flow aids (formulation permitted)
Small dosages of permitted flow aids (e.g. food-grade amorphous silica) coat particle surfaces, reduce interparticle contact points and suppress liquid bridge formation.
Dosage must follow food regulation limits and should not interfere with protein functionality or end-product properties.
Packaging design
Use moisture-barrier packaging films (aluminium composite or high-barrier plastic). Seal immediately after filling to isolate powder from ambient humidity. Purge headspace with dry air if required.
Post-process conditioning and quality monitoring
Cool powder fully before packaging; hot powder sealed inside bags will release internal moisture and cause internal caking.
Periodically test caking tendency, flow index and moisture content as in-process quality checks.
Flow aids improve anticaking performance but may alter functional properties such as emulsification and water absorption. Over-cooling or dehumidification also increases production energy cost.
