Agglomerated food powder
Agglomerated food powder is a unit operation during which native particles are assembled to form bigger agglomerates, in which the original particle can still be distinguished. Agglomeration can be achieved through processes that use liquid as a binder (wet methods) or methods that do not involve any binder (dry methods). Description. The liquid used in wet methods can be added directly to the product or via a humid environment. Using a fluidized bed dryer and multiple step spray drying are two examples of wet methods while roller compacting and extrusion are two examples of dry methods. Advantages  of agglomeration for food include: Disadvantages of food agglomeration: Particle size distribution is an important parameter to monitor in agglomerated food products. In both wet and dry agglomeration, particles of undesired sizes must be removed to ensure the best possible finished product performance. High-powered cyclones are the most common way to separate undesired fine particles (or "fines") from larger agglomerates (or "overs"). Cyclones utilize the combination of wind power and the different densities of the two products to pull the fines out of the mix. The fines can then be reworked through the agglomeration process to reduce yield loss . In contrast, shaker screens are often used to separate out the overs from the rest of the product. The overs can be reworked into the process by first being broken into smaller particles. Wet agglomeration methods. Wet agglomeration is a process that introduces a liquid binder to develop adhesion forces between the dry particles to be agglomerated. Mixing disperses the liquid over the particles evenly and promotes growth of the aggregate to the desired size. A final drying step is required to stabilize the agglomerates. In all wet agglomeration methods, the first step is wetting the particles. This initiates adhesion  forces between the particles. The next step, nucleation, is the process by which the native particles come together and are held with liquid bridges and capillary forces. Then, through coalescence or the growth phase, these small groups of particles come together to create larger particles until the particles are the desired size. Consolidation occurs as the agglomerates increase in density and strength through drying and collisions with other particles. Mixing as the powder dries also causes some particles to break and erode, creating smaller particles and fines. To achieve the correct particle size, erosion and growth must be balanced. The  last step in wet agglomeration is the final stabilization through drying. The agglomerated particles are dried to less than 5% water content, and cooled to below their glass transition temperature. Wet agglomeration falls into two categories based on method of agitation: Mechanical mixing and pneumatic mixing. Dry agglomeration methods. Dry agglomeration is agglomeration performed without water or binding liquids, instead using compression only. Roller compaction. Roller compaction is a process in which powders are forced between two rolls, which compress the powders into dense sticks or sheets. These sticks or sheets are then ground into granules. Material properties will affect  the mechanical properties of the resulting granules. Food particles with crystalline structures will deform plastically under pressure, and amorphous materials will deform viscoelastically. Roller compaction is more commonly used on individual ingredients of a finished powdered food product, than on a blend of ingredients producing a granulated finished product. Some advantages of roller compaction are Disadvantages: Examples of agglomerated food powders: Sucrose, sodium chloride, monosodium glutamate and fibers. Extrusion. Extrusion is executed by mixing the powder with liquid, additives, or dispersants and then compressing the mixture and forcing it through a die. The product is then dried and broken down  to the desired particle size. Extruded powders are dense. Extrusion is typically used for ingredients such as minerals and highly-hygroscopic products which benefit from reduced surface area, as well as products that are subject to oxidation. Extrusion for agglomeration should not be confused with the more common food extrusion process that involves creating a dough that is cooked and expands as it passes through the die.