Caking and clumping are ubiquitous in the food and pharmaceutical industries. Where there is free-flowing powder, there will usually be lumps and clumps.
When powders are exposed to moisture, they absorb water vapor. At first, the water sits on the surface of the powder particles, but soon the water begins to penetrate the particles. The powder stops flowing freely, and the problems start.
Moisture content can’t predict
Free-flowing powders move through five stages of caking. The particles become wet, then sticky; they agglomerate, compact, and finally reach the liquefaction stage. The process is affected by many factors, including particle shape and size, applied pressure, and chemical composition. Predicting and avoiding caking comes down to just three: time, temperature, and water activity.
The critical water activity
Products cake or clump at a specific water activity (aw). This critical water activity is different for each product, but it can often be determined using a high-resolution isotherm. Once you know the critical water activity, if you keep the product below that value, you will avoid clumping.
Adding ingredients at higher water activities can change the water activity of the product. In addition, high ambient humidity and increases in temperature can raise the water activity of the product.
3 simple steps prevent caking and clumping
Just DON’T add water
Adding moisture will increase the water activity. Moisture can be adsorbed from high humidity air or other ingredients at a higher water activity.
Measure twice, process once
If ambient humidity is higher than the water activity of a powder, the powder will clump. If the water activity of an added ingredient is higher, the powder will clump. Measure to avoid problems.
Get a high-resolution isotherm
A DDI isotherm pinpoints the water activity above which caking and clumping occur. Figure 1 shows what a DDI isotherm looks like. DVS studies predict how long it will take for a product to take on moisture under various conditions. This allows product developers to study (for example) the amount of time it will take for a powder to reach 0.45 aw if room humidity is 60%.