What do baked goods, food aid supplies, and baby formula have in common? They all often rely on milk powder. A strange yet common ingredient, milk powder is, at its core, regular milk dehydrated by the partial removal of water. Because the ingredient is nonperishable, the cost of transportation and storage for milk powder is significantly lower than its liquid counterpart, making it just as valuable to those living in developing countries and temporary shelters as it is to hikers setting out on a long trip. Although dehydrated milk sounds like basic enough of a concept to grasp, I still wonder what goes into making fresh milk shelf-stable. 

Popular brands of milk powder, like Bob’s Red Mill and Carnation advertise that people should feel confident using the product any time they’d typically add milk, from sauces to quick breads to smoothies. Both brands of milk powder are either made with just milk or with milk and added nutrients to replace those lost during the dehydrating process: Bob’s Red Mill’s ingredient list reads “non-fat dry milk,” and Carnation’s is “skim milk powder, vitamin A palmitate, cholecalciferol (vitamin D3).”

Since these products contain only milk, milk powder’s stability clearly comes from the dehydrating process. Skim milk powders are typically produced from a process known as spray drying, during which small emulsion droplets are reduced into powder. 

After raw milk is pasteurized, it is preheated, evaporated, and heated again to a concentrated mixture of milk solids. The mixture is then spray dried, a process that relies on atomization, also known as reducing liquid to mist. The concentrated milk is sprayed into a heated chamber, during which it reduces into fine particles. Through this process, milk retains the ability to return to its original state when rehydrated with water According to Codex standard, milks of various fat and protein levels can spray dried to a maximum moisture content of 5 percent. 

After the milk is spray dried, it’s typically dried again to remove any lingering moisture before packaging. From there, it’s transported to grocery store shelves and emergency food warehouses, where it can theoretically stay stable for years.