Caking is a moisture problem with a mechanical outcome. Fruit powders are dominated by low molecular weight sugars, those sugars are hygroscopic, and once the powder picks up enough water the particle surfaces soften and fuse into bridges. The drum arrives as a powder and becomes a block.
Freeze-dried powders are the worst affected because their porous structure exposes an enormous surface area. A freeze-dried fruit powder left open on a factory floor at high ambient humidity can begin taking up water within minutes.
The parameter that predicts caking is water activity at a stated temperature, not moisture percentage. Two powders at identical moisture can sit either side of the sticking point depending on the sugar profile and the carrier, which is why a specification that carries only a moisture figure does not protect the buyer.
The controls, in order of effectiveness:
- An aluminium foil laminate liner rather than plain polyethylene, because polyethylene is not a moisture barrier at the level this product needs
- A desiccant sachet or a nitrogen headspace on high-value material
- A stated storage temperature and relative humidity ceiling in the contract, and a warehouse that is actually monitored against it
- A written rule about how quickly an opened drum is resealed
- A water activity limit on the specification with the method named
Anti-caking agents are permitted additives under Regulation (EC) No 1333/2008 within the authorised uses and levels, and they are declarable ingredients. They help a powder resist caking; they do not rescue one that has already absorbed water. Once a drum has fused, sieving does not restore free-flowing behaviour and the lot is effectively downgraded.