I. False Caking (Soft Caking)

Definition: Temporary agglomeration caused by physical forces, with no chemical changes. The powder can be easily restored to its original state.

Causes:

• Physical adsorption: Electrostatic forces or van der Waals forces between fine particles, especially prominent in high-fineness powders.
• Mechanical compression: External pressure from stacking or transportation reduces particle gaps, leading to loose agglomeration.
• Minor moisture adsorption: Adsorption of small amounts of moisture (humidity < 60%) forms weak liquid bridges, but not enough to induce dissolution.
• Temperature fluctuations: Brief condensation of moisture on particle surfaces due to temperature changes, promoting adhesion without altering crystal structure.

Characteristics:

• Morphology: Loose, flocculent clumps that break easily under light pressure; no glossy surfaces, with visible particle gaps.
• Properties: Solubility, pH, and activity remain identical to the original powder; complete dispersion after sieving or stirring.
• Microscopy: Individual particles with clear edges, no crystal fusion or new phases observed.
• Stability: Does not harden over time; may loosen spontaneously under improved storage conditions.

Treatment & Prevention:

• Treatment: Pass through an 80-100 mesh sieve or stir gently to disperse agglomerates.
• Prevention:
  • Store in sealed containers with silica gel desiccants (relative humidity < 60%);
  • Avoid heavy stacking; use shallow trays for subpackage；
  • Maintain stable temperature (15-25℃) to prevent moisture condensation.

II. True Caking (Hard Caking)

Definition: Permanent agglomeration caused by chemical changes or irreversible physical processes, often altering powder properties and making full recovery difficult.

Causes:

• Dissolution-recrystallization: High humidity (> 70%) leads to excessive moisture absorption, dissolving part of the powder; subsequent evaporation causes recrystallization, forming strong crystal bridges (common in sodium benzoate).
• Chemical reactions: Reaction with atmospheric components (e.g., CO₂, moisture) generates new substances. For example, calcium propionate may react with CO₂ in humid air to form calcium carbonate, hardening the cake.
• Melting-solidification: Exposure to temperatures exceeding the powder’s melting point (e.g., benzoic acid melts at 122℃) causes partial melting, which solidifies into dense clumps upon cooling.
• Polymorphic transformation: Humidity-induced crystal form changes (e.g., in calcium propionate) lead to volume contraction and particle adhesion.

Characteristics:

• Morphology: Hard, dense clumps or plates with smooth, glossy surfaces; require forceful grinding to break, with residual hard mass even after crushing.
• Properties: Reduced solubility (due to dense crystallization); possible pH shifts (e.g., sodium benzoate may become more alkaline due to hydrolysis).
• Microscopy: Merged particles with indistinct boundaries; continuous crystal structures or new crystalline phases observed.
• Stability: Hardens further over time; may develop mold (in high humidity) or degrade active ingredients.

Treatment & Prevention:

• Treatment: Pulverize lightly caked samples and test for purity/activity; discard severely caked or unqualified products to avoid food quality issues.
• Prevention:
  • Use vacuum-sealed or aluminum foil packaging to isolate moisture and air;
  • Store in cool, dry warehouses (humidity < 50%, temperature < 20℃), away from heat sources and acidic/alkaline substances;
  • Shorten storage periods, prioritize using newer batches;
  • Add anti-caking agents (e.g., silicon dioxide) to highly hygroscopic additives (e.g., sodium benzoate) and use small packaging.

Comparison Table

Heathy Chemical reserves the final right of interpretation for the article.