Triboelectric charging of 3-in-1 coffee mixes: Formulation and fouling

In powder processing, fouling is a serious and common issue. This is caused by powder adhesion on processing surfaces, leading to clogging and disruption. Most of the time, powder adhesion is due to triboelectric charging. Electrostatically charged powder adheres to surfaces, accumulating and eventually leading to blockage of channels (e.g., transfer pipes, etc.). This production problem is usually discovered during manufacturing scale-up. The characteristics of the powder correlate with the extent of triboelectric charging, and thus it is possible to predict this production problem during the product formulation/development stage. A case study to predict and prevent fouling for 3-in-1 coffee powder and its components (sugar, coffee, and creamer) was investigated. First, the electrostatic charge of the commercial 3-in-1 coffee mixes and their individual ingredients were measured. Analytical tests were also conducted to correlate the electrostatic charge to the components in each ingredient. For sugar, higher mineral levels lead to less negative charge. For coffee, powders with higher caffeine levels lead to more negative charge. For creamer, a polynomial correlation was observed from 1 to 35% fat, with negative charge at 1–8% fat content, zero charge at 8–10%, and positive charge at 10–25% fat. Beyond 25% fat, charge is reduced significantly along with undesirable aggregate formation. This relation between fat percentage and charge holds even after the creamer is mixed with sugar and coffee to form 3-in-1 mixes. Hence to reduce charge and therefore reduce fouling, sugar with high mineral content, coffee powder with low caffeine content, and creamers with low fat content (<10%) are recommended.