Caking and Agglomeration Prevention – Keeping Powders Free-Flowing from Silo to Scoop

This topic is part of the SG Systems Global powder handling, ingredient stability and dry-operations glossary.

Updated December 2025 • Bulk Density Testing, Fines & Coarse Particle Distribution, Powder Cohesiveness Classification, Powder Conditioning, Particle Size Reduction & Milling Control, Hygienic Equipment Design for Powder Systems, Dust Explosion Hazard • Ingredients & dry mixes, bakery premix, nutraceuticals, pharma, agrochemicals, detergents, plastics, food & beverage

Caking and agglomeration prevention is the set of strategies used to stop powders turning into unwanted lumps, blocks or “brick-in-a-bag” during storage, transport and processing. Caking happens when particles bond together irreversibly under moisture, temperature, pressure or time. Agglomeration can be either deliberate (engineered granules) or accidental: unplanned clumps that wreck flow, slow dissolution, jam feeders and prompt frantic hammering on silos at three in the morning. For plants that live on dry ingredients, preventing caking and uncontrolled agglomeration is the difference between a stable, predictable line and a constant firefight.

“If your solution to powder caking is ‘hit the hopper with a mallet,’ you don’t have a process – you have a ritual.”

1) What Caking and Agglomeration Are in Practice

In powder operations, two phenomena show up on the shop floor:

• Caking: Formation of hard, often irreversible solid masses within a powder bed. Caked product may adhere to walls, form solid blocks in bags or IBCs, or create hard lenses in silos that collapse suddenly.
• Uncontrolled agglomeration: Formation of soft to firm lumps or clumps – not as hard as fully caked material, but enough to jam feeders, plug screens and create “grit” in finished product.

Both are symptoms of deeper mechanisms: moisture migration and crystallisation, glass transitions, local melting, capillary bridges, chemical reactions, or mechanical compaction. Prevention means addressing those mechanisms, not just installing bigger lump-breakers and telling operators to swing harder with hammers.

2) Key Mechanisms Behind Caking and Agglomeration

Caking rarely has a single cause. Common mechanisms include:

• Moisture sorption & desorption: Hygroscopic powders absorb water at higher relative humidity, then partially dissolve and recrystallise at contact points, forming solid bridges.
• Glass transition and softening: Amorphous components (e.g. spray-dried flavours, sugars) soften or become rubbery above their glass-transition temperature (T_g), allowing particles to fuse.
• Capillary condensation: Localised high humidity in pores and contact points creates liquid bridges that solidify with time.
• Pressure and creep: Tall silos and stacked bags subject lower layers to static load, causing particles to rearrange, deform and bond over time.
• Temperature cycling: Repeated warm/cool cycles drive condensation, dissolution, crystallisation and phase changes that lock particles together.
• Chemical reactions: Reactive components (e.g. certain salts, acids, alkalis) can slowly react, forming solid phases at contacts.

Effective prevention starts with identifying which of these mechanisms is dominant for a given product at its actual storage and processing conditions – not at idealised lab conditions that the plant never sees in July or in a sea container.

3) Role of Particle Size, Fines and Cohesiveness

Fines and coarse particle distribution and cohesiveness heavily influence caking risk:

• More fines: Higher surface area and more contact points; accelerates moisture sorption, sintering and capillary-bridge formation.
• Cohesive powders: Already prone to forming low-density structures; under pressure and humidity they evolve into hard cakes.
• Broad PSD: Fines filling voids between coarser particles can create dense packings, reducing free volume and increasing conduction of moisture and heat.

Poorly controlled milling, repeated rework and attrition in conveyors all tend to generate fines over time, nudging powders from “annoyingly sticky” toward “fully caked.” Watching PSD tails alongside caking complaints is often the fastest way to see this drift happening in real time.

4) Environmental Drivers – Temperature, Humidity and Conditioning

Environment is one of the biggest levers you have. See Powder Conditioning (Temperature & Humidity Control) for detail; in short:

• Relative humidity (RH): Crossing critical RH thresholds (tied to a material’s sorption isotherm) dramatically increases caking risk.
• Temperature: Higher temperatures increase diffusion and may push amorphous components above T_g; cooling through dew point drives condensation in headspaces and on cold surfaces.
• Time: Caking is often time-dependent; hours in a hopper may be fine, weeks in a warm, humid warehouse may not.

Environmental control strategies for caking prevention include:

• Conditioned storage rooms for high-risk ingredients.
• Dew-point-controlled compressed air for conveying, aeration and packaging.
• Insulated or climate-controlled silos to avoid wall “cold spots” and condensation bands.
• Defined maximum storage periods at given RH/temperature, enforced via WMS shelf-life and location rules.

It is usually cheaper to keep powders within a safe “envelope” than to fix caking after it has formed – especially in tall silos and ships or containers where mechanical intervention is expensive and risky.

5) Caking in Silos, Hoppers and Bins

Caking shows up in storage vessels as:

• Rings and rinds: Hardened layers on walls, often at previous fill levels or where condensation has occurred.
• Dead zones: Areas where product never fully empties and slowly turns into a solid mass.
• Hard “lenses” above outlets: Caked regions that bridge across outlets, causing bridging and rat-holing.

Prevention levers include:

• Mass-flow design: Hoppers that ensure all material moves, minimising stagnant pockets where caking can progress.
• Smooth, hygienic surfaces: As per Hygienic Equipment Design for Powder Systems, to reduce adhesion and make incidental build-up easy to dislodge.
• Controlled residence time: FIFO rules enforced by Ingredient Conditioning & Storage and WMS logic, avoiding “silos that never quite empty.”
• Avoiding over-aeration: Uncontrolled air fluidization that drives moisture-laden air through beds and encourages bridging and condensation.

Retrofitting anti-caking measures on fundamentally bad silo designs is hard; in many cases, a serious flow and caking review leads to hopper inserts, new cones or dedicated silos for the worst offenders rather than perpetual dependence on hammers and vibrators.

6) Caking in Bags, Drums and IBCs

Caking in packages is a frequent source of customer complaints (“brick in a bag”) and internal handling problems. Drivers include:

• Stacking pressure: Heavy stacks on pallets compress lower layers; powders creep and bond over time.
• Permeable packaging: Bags or liners that allow moisture ingress and egress, especially in humid or coastal environments.
• Temperature cycling: Uninsulated storage subject to day/night and seasonal swings, plus container journeys.

Prevention tactics:

• Use liners or multi-layer bags with low water-vapour transmission for hygroscopic products.
• Limit stack heights and pallet configurations based on caking tests, not just warehouse convenience.
• Control pre-packing powder condition; avoid packing immediately after hot or wet processes.
• Use anti-caking agents or engineered agglomerates where appropriate to stabilise flow and density.

In many B2B ingredient businesses, small tweaks to packaging material and stack limits radically reduce “brick-in-a-bag” complaints without any change to formulation – provided the organisation is willing to accept a slight increase in packaging cost or warehouse height usage in exchange for higher usable yield and happier customers.

7) Formulation Levers – Anti-Caking Agents and Agglomeration Design

Sometimes the fastest way to stop caking is to change the powder, not the plant. Options include:

• Anti-caking agents: Flow aids such as silicates, phosphates or starches that absorb moisture, coat surfaces or reduce contact area between base particles.
• Engineered agglomeration: Turning very fine, cohesive powders into robust granules with controlled strength and porosity (as opposed to uncontrolled caking).
• Surface treatments: Hydrophobic coatings or encapsulation to reduce moisture sorption and tackiness.
• PSD optimisation: Adjusting milling, classification and de-aeration to control fines while still meeting product-performance requirements.

Any of these should be evaluated via stability and conditioning studies that simulate real storage and handling conditions – warehouses, sea freight, seasonal extremes – not just 7 days in a lab incubator. Data from bulk density testing, flow indices and caking tests at different RH/temperatures should feed into specification and label claims, not sit forgotten in development reports.

8) Mechanical Design and Handling Practices

Mechanical handling can either prevent or accelerate caking and agglomeration:

• Gentle conveying: Avoiding high-impact elbows, long drop heights and overly aggressive vibratory conveying that generate fines and compaction.
• Reasonable vibration: Enough to keep powders moving; not so much that you pre-compact them into semi-solid beds.
• Dead-leg elimination: As per Hygienic Equipment Design, removing pockets where powder can sit under stress and “age” into cakes.
• Flow aids used intelligently: Air pads, mechanical agitators and knockers sized and interlocked to prevent both chronic compaction and uncontrolled “avalanche” release.

Change-control and design reviews should treat “how does this change affect caking risk?” as a standard question – especially for projects involving new silos, conveyors, valves or extended storage time. Many caking problems start as small engineering optimisations (more vertical height, more stacking, higher conveying velocities) that looked harmless in isolation.

9) Sampling, Testing and Quantifying Caking Propensity

To move beyond anecdote (“it caked badly last summer”), sites can develop simple caking tests:

• Storage tests: Powders stored in small jars or cells under controlled RH/temperature for defined times, then assessed for hardness, flow and re-dispersibility.
• Compression tests: Applying known loads to powder beds for defined periods to simulate silo or stack pressures, then measuring force required to break up cakes.
• Flow tests after storage: Comparing flow through standard funnels or orifices before and after conditioning.
• Density and PSD after storage: Re-testing bulk density and tail fractions to see how storage changes structure.

Results can be incorporated into material masters: “Caking class 1–4” alongside cohesiveness classes, with recommended maximum residence times and environmental envelopes. That gives planners, warehouse and engineering a concrete basis for decisions such as “you simply cannot stack this product five pallets high in a non-conditioned warehouse for six months and expect it to flow.”

10) Caking, Clogs and Foreign-Material / Safety Risk

Caking and uncontrolled agglomeration are not just flow problems; they also create foreign-material and safety risks:

• Hard lumps: Can appear as FM in finished product, driving complaints and recalls; see Foreign Material Risk Assessment (FMRA).
• Sudden blockage release: Large caked masses breaking loose in silos can create surges, equipment overloads and, in extreme cases, structural damage or dust clouds.
• Manual intervention: People banging silos, entering bins or cutting open stuck bags create obvious safety hazards.

Risk assessments and procedures should explicitly recognise that caking is a credible deviation mode. Controls should include safe methods for clearing blockages (remote tools, flow aids, isolation) and clear prohibitions on hazardous practices like entering a bin with overhead product or standing under potentially caked outlets during mechanical poking.

11) Interaction with Cross-Contact and Hygiene Controls

Caking also interacts with cross-contact prevention and hygiene:

• Residues in dead zones: Caked material can remain in equipment across product and allergen changeovers, undermining cleaning and segregation plans.
• Microbial risk: In moisture-sensitive products (e.g. dairy, nutritionals), caked regions can retain moisture and provide niches for microbial growth.
• Cleaning difficulty: Caked powder is far harder to remove than free-flowing powder, increasing cleaning time and the temptation to accept partial removal.

For allergen- or micro-critical lines, caking should be treated as a hygiene non-conformance, not just a flow nuisance. Equipment that consistently cakes may require design changes, reduced campaign lengths or product-specific restrictions to maintain credible cleaning validation and cross-contact control.

12) Link to Dust Explosion Hazard (NFPA 652, ATEX)

Caking and dust-explosion risk are connected in two ways:

• Cake break-up: Mechanical breaking of caked layers can generate substantial fines and airborne dust, momentarily increasing explosion risk; see Dust Explosion Hazard (NFPA 652, ATEX).
• Hidden deposits: Caked dust in ducts, filters and equipment may be overlooked in DHAs until disturbed by an upset, providing fuel for secondary explosions.

Dust Hazard Analyses should consider cakes and hard deposits specifically, not just loose dust layers. Cleaning and inspection regimes need to include potential caking sites, and blockage-clearing procedures must factor in the risk of sudden dust release into confined spaces with ignition sources present.

13) Governance – Putting Caking Prevention into the QMS

To stop caking and agglomeration being an eternal “operator problem,” they need to be pulled into the Quality Management System (QMS) and Quality Risk Management (QRM):

• Risk registers: Caking risks identified and prioritised for key products and lines.
• Specifications: Storage-time, RH/temperature envelopes and PSD tail limits written into material and product specs where caking is relevant.
• Change control: Process, formulation, packaging and storage changes evaluated for impact on caking propensity before approval.
• Monitoring & PQR: Caking-related deviations, complaints and yield losses trended as part of Product Quality Review (PQR) and used to justify investments in conditioning, packaging or equipment upgrades.

Over time, this moves caking from “bad luck in hot weather” to a managed risk with documented controls, owners and improvement plans – the same way serious organisations treat microbiology, allergens or dust explosions.

14) Implementation Roadmap – Reducing Caking and Agglomeration in Practice

A pragmatic roadmap for an Ingredients & Dry Mixes facility might include:

• Step 1 – Identify problem products: List powders with frequent flow issues, “brick-in-bag” complaints, hammering incidents or silo blockages.
• Step 2 – Characterise mechanisms: For those products, gather data on PSD tails, bulk density, moisture sorption, cohesiveness class and storage conditions.
• Step 3 – Quick wins: Tidy up obvious environment/handling contributors – RH/temperature control, stack heights, silo FIFO rules, residence times.
• Step 4 – Design and formulation review: For persistent offenders, conduct deeper reviews of silo/hopper design, conveying, packaging and formulation (including anti-caking agents and agglomeration options).
• Step 5 – Codify controls: Add caking-related rules (max storage time, stack limits, conditioning requirements) into WMS/MES, SOPs and specs; train operators and warehouse teams.
• Step 6 – Monitor and refine: Track caking incidents, complaints, rework and yield losses; tie improvements back to specific actions and update risk registers and design standards accordingly.

The aim is not to eliminate caking risk completely – for some powders, that is impossible without major formulation changes – but to push it into a controlled, predictable range where flow, yield and safety are not at the mercy of weather, shipping routes and whoever last adjusted the aeration valves.

15) FAQ

Q1. How do we tell if caking is mainly a moisture problem or a pressure/time problem?
A practical approach is to run small storage tests under controlled RH at low and high compaction pressures. If caking occurs even at low pressure but increases sharply with RH, moisture and sorption behaviour are dominant. If caking is minimal at realistic RH but increases dramatically with pressure/time (e.g. simulated stack or silo loads), then mechanical creep and consolidation are more important. In many real cases both mechanisms contribute; tests help you weight where to invest first – conditioning/packaging or mechanical design/stack limits.

Q2. Can we rely purely on anti-caking agents instead of environmental and design controls?
Not safely. Anti-caking agents are powerful tools but not magic. Their performance depends on correct dosing, distribution, compatibility and regulatory constraints. Over-reliance on additives can mask underlying design or storage problems and create new issues (label claims, taste, regulatory status). A balanced strategy uses anti-caking agents alongside environmental control, good hopper design and sensible handling rules.

Q3. Does more vibration always help prevent caking?
No. Moderate vibration can help keep powders moving and prevent incipient bridges, but excessive or continuous vibration can compact beds, reduce void space and actually accelerate caking and densification – particularly in tall silos and stacked bags. Vibration regimes should be specified and tested, not left to ad hoc operator judgement.

Q4. How soon should we be worried about caking in a new product?
Immediately in development. If a new powder is hygroscopic, has fine PSD tails, or contains amorphous components, caking risk should be evaluated via targeted conditioning and storage tests before full-scale launch. Waiting for field complaints is a slow, expensive and reputation-damaging way to discover that a formula or packaging concept is not robust to real-world conditions.

Q5. What is a practical first step if we have chronic caking in one silo or product line?
Start with a focused reality check: document environmental conditions, residence times, fill/empty patterns and any unusual geometry or flow aids on that silo or line. Sample powder from different heights and wall regions, test PSD, moisture, bulk density and simple caking tests after controlled conditioning. In parallel, walk the process for obvious condensation points, dead legs and stacking practices. Often, a combination of slightly improved conditioning, adjusted FIFO rules and modest mechanical changes (e.g. insulation, smoothing of internal surfaces, re-tuned aeration) yields a disproportionate reduction in caking before you even consider major capital or formulation changes.

Related Reading
• Powder Behaviour & Flow: Powder Cohesiveness Classification | Fines & Coarse Particle Distribution | Air Fluidization & Powder Aeration | Vibratory Conveying Dynamics
• Conditioning, Storage & Safety: Powder Conditioning (Temperature & Humidity Control) | Ingredient Conditioning & Storage | Silo Rat-Holing & Bridging | Dust Explosion Hazard (NFPA 652, ATEX)
• Design, QA & Process Control: Hygienic Equipment Design for Powder Systems | Bulk Density Testing | Particle Size Reduction & Milling Control | Foreign Material Risk Assessment (FMRA)