Spoilage in food manufacturing is often attributed to surface hygiene or downstream contamination. However, many issues originate much earlier in the production process, specifically in the early bulk solids handling stages. The equipment that stores or moves bulk solids can influence the flow regime experienced by the material, and under certain operating conditions, regions of slow or stagnant material can develop. These areas hold product long enough for microbial growth to occur, driving spoilage and forming a persistent source of contamination that affects every batch that follows. Handling solutions for food solids, such as powder and bulk solids, can address the root causes of stagnation so that materials continue to move consistently and predictably through the handling and processing stages of food production.
Why Spoilage Occurs in Food Solids Handling Systems
Stagnant Regions as Initiation Points for Microbial Growth
Stagnant regions, areas where solid material slows, settles, or remains undisturbed, can develop in crevices, dead-legs, occluded corners, and low-flow pockets within silos, hoppers, chutes, and conveyors. Once material comes to rest, moisture and residues accumulate, forming the conditions that allow microbes to attach and form biofilms. These biofilms can adhere strongly to surfaces and persist even after routine cleaning, continually reintroducing spoilage organisms into the product stream. Because material held in place continues to age and degrade, it provides nutrients that support ongoing microbial activity. Preventing spoilage, then, depends on avoiding situations where solids remain stationary long enough for microbial activity to take hold.
Why Solid Foods Amplify the Problem
Solid and semi-solid foods can amplify stagnation risks because many materials shed fine particles that migrate into tight spaces within common solids-handling equipment such as silos, hoppers, and transfer chutes. Powders that cake, blends that segregate, and sticky ingredients that cling to surfaces all contribute to localized build-up. Small pockets of retained material often sit outside the main flow path and are not cleared during normal operation, gradually becoming dependable harborage sites for microbial growth. The resulting quality impact may be subtle initially, but as production continues, spoilage episodes can become more frequent and difficult to control.
Food Solids Handling Solutions
1. Hopper and Silo Designs That Ensure Mass Flow
Mass flow hoppers and silos are engineered so that all material moves during discharge, preventing older powders from remaining in the vessel. This behavior is achieved by configuring hopper geometry and surface characteristics to match a material’s flow properties. To obtain mass flow, hopper walls must be steep enough and smooth enough for material to slide along the surface rather than form stagnant ratholes or sidewall deposits. The outlet must be sized large enough to overcome arching or plugging and the feeder must be designed to feed across the entire hopper outlet. Flow property test data is needed to determine those values. The hopper angle required for mass flow is ascertained from wall friction tests of the powder tested against the proposed hopper wall material of construction. Cohesive strength test results also provide the outlet size required to prevent arching/plugging. Moreover, compressibility tests provide the bulk density which is a necessary input to design. The feeder must be designed to guarantee that the material discharges uniformly across the entire cross-section. When these design elements work together, the hopper or silo operates in a first-in-first-out pattern that limits retention time and reduces the likelihood of microbial spoilage.
2. Eliminating Material Hang-Up Through Surface and Geometry Selection
Many food solids tend to adhere to internal surfaces, forming points where material can accumulate and interrupt normal flow, increasing the risk of spoilage. Selecting appropriate stainless-steel finishes, applying low-friction liners for frictional powders based on the flow property test data, and shaping internal geometry to remove upward-facing ledges helps minimize residue build-up. In turn, continuous internal surfaces prevent material from settling, reducing the likelihood of microbial attachment and biofilm development.
3. Applying Flow-Aid Devices to Maintain Movement in Difficult Solids
Some solids, such as high-fat powders, protein blends, dehydrated fruit pieces, and hygroscopic ingredients like sugars or milk powders, resist movement using only gravity alone. Sometimes additional measures are required to initiate flow. Vibrators, shakers, and air cannons are designed to break up compacted material. However, these flow-aid devices can overcompact powders, worsening powder flow. Cohesive strength test results analyze whether or not material is a good candidate for flow aids Additionally, stick shape (high-aspect ratio) or semi-solid products may benefit from internal agitation or live-bottom systems. Material testing will provide the answer if flow aids are needed and if so, what type would work best.
4. Selecting Appropriate Feeders to Ensure Even Product Withdrawal
Feeders control how material exits a vessel, making them critical for preventing uneven withdrawal. Isolated pockets of product can remain when the wrong feeder is used, increasing retention time and contributing to spoilage. Belt feeders, screw feeders, vibratory feeders, and rotary valves each impart distinct flow characteristics suited to specific material types:
- Screw feeders- effective for cohesive powders and blends requiring controlled, positive displacement. They are also fully enclosed.
- Belt feeders- suitable for fragile flakes, granules, or friable materials that need gentle handling with wedge shaped hoppers. They only work well with a proper interface between the hopper and belt feeder to withdraw material from the entire hopper outlet.
- Vibratory feeders- ideal for free-flowing powders and uniform particulates that respond well to low-shear movement and don’t compact with vibration.
- Rotary valves- useful for metering powders and small granules at a steady rate while maintaining an airlock.
Choosing a feeder that activates the full outlet area helps ensure complete discharge and reduces the likelihood of the formation of stagnation zones.
5. Designing Transfer Chutes and Conveyors to Avoid Build-Up
Transfer points often generate conditions where material can slow, accumulate, or become trapped. To avoid this, transfer chutes are shaped to maintain material velocity and guide the stream smoothly through changes in direction. Features such as curved transitions, chute liners with low-friction surfaces, and properly designed feed onto the downstream conveyor or equipment help prevent material from settling on internal walls. For conveyors, belt scrapers, sealed edges, and engineered transfer points minimize the build-up of fines, while inspection and clean-out access allow operators to remove any residual material that does form. Designing these systems to limit areas where solids can lodge reduces the potential microbial harborage, and thus spoilage.
Reducing Spoilage With Jenike & Johanson
Spoilage in food solids handling can be controlled through solutions that prevent material from slowing, settling, or becoming trapped in areas where microbes can establish themselves. Jenike & Johanson can help food manufacturers prevent spoilage by characterizing material flow properties, designing mass flow storage systems, integrating the right feeders, and troubleshooting equipment where stagnation already occurs. These services provide targeted, evidence-based solutions that align equipment performance with material behavior. Discover more about how Jenike & Johanson can lower spoilage risks in your solids handling operations by speaking with our engineering team.
