Vacuum coater: A post-processing system that uses negative pressure to force liquid additives — oils, fats, enzymes, vitamins — deep into the core of feed pellets, rather than applying them to the surface. The difference between surface coating and vacuum infusion isn't a technical detail. It determines the quality ceiling of your finished feed.

Conventional drum coaters spray oil onto tumbling pellets. Beyond 3–5% oil inclusion, the surface becomes greasy, pellets clump together, packaging becomes difficult, and excess surface oil leaches into the water during feeding — wasting nutrition and polluting the pond.

Vacuum coating eliminates this ceiling entirely.

The entire process takes place inside a sealed chamber and runs automatically in four stages:

1. Step 1 — Load and seal Feed pellets enter the coating chamber. The chamber door is sealed airtight.
2. Step 2 — Draw vacuum A vacuum pump reduces internal pressure to the set level (typically -0.08 to -0.095 MPa). Air is evacuated from the pellet's porous structure, leaving the internal matrix open and receptive.
3. Step 3 — Inject liquid With the chamber under vacuum, oil or liquid additives are metered in through a precision dosing pump. The pressure differential drives liquid rapidly into the pellet interior — not onto the surface.
4. Step 4 — Restore pressure and discharge Atmospheric pressure is gradually restored, compressing the absorbed liquid further into the pellet matrix. The chamber opens and coated pellets are discharged.

A typical batch cycle runs 5–15 minutes depending on batch size and vacuum parameters.

Premium fish feeds — salmon, trout, eel, grouper — require high fat levels to meet the energy demands of carnivorous species. Vacuum coating is a standard process in fish feed production; depending on the feed type, 4 to 40% oil can be applied to extruded fish feed after production.

Drum coating cannot come close to this. Surface oil above 5% causes pellets to clump, makes packaging difficult, and results in oil leaching into the water column during feeding — wasting both nutrition and money.

Vacuum coating gives feed formulators the freedom to design high-energy, high-fat diets without being constrained by the limits of the coating equipment.

Water stability is a primary quality indicator for aquatic feed. Under vacuum conditions, pellets expand slightly and absorb liquid additives inside their pores — not on the surface — resulting in reduced surface oil and better water matrix bonding, which significantly improves water stability.

For shrimp feed, water stability requirements typically exceed 4–6 hours without disintegration. Surface-coated oil dissolves into the water column within minutes, carrying away nutrients and accelerating pellet softening. Vacuum-coated pellets maintain structural integrity far longer.

Pelleting and extrusion operate at 80–130°C. Enzymes, probiotics, and heat-sensitive vitamins added before this stage lose a significant portion of their activity. The labeled inclusion rate in the formula and the actual active content in the finished pellet can be very different.

Vacuum coating technology may also be used to apply fat-soluble and water-soluble vitamins to feed after pellet production, reducing the required inclusion levels — since conventional pelleting and extrusion processes cause substantial vitamin losses.

Vacuum coating is performed at ambient temperature after drying. Enzyme and vitamin activity is preserved at its highest possible level. The same formula produces genuinely better-performing feed.

Strongly recommended:

• Premium aquatic feeds: salmon, trout, eel, grouper, sea bass (high fat requirement ≥15%)
• Shrimp feed: high water stability demands, liquid additive penetration is critical
• Pet food: cat and dog kibble require uniform palatant absorption for consistent palatability
• High-value specialty feeds: abalone, sea cucumber, and other premium aquaculture species

Evaluate based on ROI:

• Standard freshwater fish feed (oil inclusion below 5% — drum coating may be sufficient)
• Poultry compound feed (high-energy formulas may benefit; standard formulas may not justify investment)

Not recommended:

• Low-fat standard pellets: equipment investment payback period is too long
• Powdered feeds: vacuum coating requires a porous pellet structure to function; powder cannot form the pressure differential needed for absorption

We have over 20 years of process experience in aquatic and pet feed production lines. The right coating configuration depends on your feed type, target oil inclusion level, and hourly output. Visit our Products & Services page to explore complete line configurations.

Q: How do I size the batch capacity? A: Batch capacity must be matched to the output of your upstream extruder or pellet mill. Lines producing 1–3 t/h typically pair with 500–1,500 liter batch coaters. Lines at 5 t/h and above need 2,000 liters or larger, or multiple units running in parallel. Undersizing creates a production bottleneck; oversizing reduces equipment utilization and increases cycle time.

Q: How important is the vacuum level specification? A: Critical. Vacuum level determines penetration depth. -0.08 MPa is adequate for standard fish oil coating; -0.095 MPa or higher is required for deep penetration in high-fat formulas. Verify that the equipment can reach and hold the target vacuum level consistently — pump power and chamber seal quality are the variables to check.

Q: What is the practical difference between SUS304 and SUS316L stainless steel? A: SUS304 covers most standard applications. SUS316L contains molybdenum, which provides superior resistance to chloride corrosion — relevant when working with high-salt raw materials such as fish oil or astaxanthin solutions. SUS316L is also easier to clean to food-grade standards. For premium aquatic feed and pet food lines, SUS316L is the recommended specification.

Q: Manual controls vs HMI touchscreen — does it matter in practice? A: Manual control relies entirely on operator experience, and batch-to-batch consistency is difficult to guarantee. HMI touchscreen control stores recipe parameters — vacuum level, coating duration, liquid dosing volume — and allows operators to reproduce results by recalling saved settings. This reduces dependence on experienced technicians and improves production consistency. For mid-to-high-end production lines, HMI control is the practical standard.

For guidance on the right configuration for your specific operation, contact us with your feed type and production capacity. You can also browse our Solutions page for real-world examples across different feed categories and line sizes.

A vacuum coater is not optional equipment for high-end aquatic feed and pet food production. It is a core component that determines the quality ceiling of your finished product.

It solves three problems that conventional drum coating cannot: fat inclusion limits, surface oil leaching, and heat-sensitive ingredient loss. Each of these directly affects your feed's nutritional performance, water stability, and market competitiveness.

Get this equipment right, and your formulation team has more freedom, your feed quality is more consistent, and your customers keep coming back.

We don't just supply equipment. We help you design the full production line correctly from the start — from ultra-fine grinding through post-pellet coating, every stage engineered to work together.