Producing 3 mm Floating Fish Feed for Japanese Koi Fish

How We Produced 3 mm Floating Fish Feed Through Extrusion with excellent pigmentation for fish— A Practical R&D Story

Producing a perfectly floating fish feed pellet using twin-screw extruder may look simple from the outside — but in reality, it requires careful control of density, moisture, temperature, and mechanical energy inside the extruder.

This is the story of how we successfully produced 3 mm floating fish feed with excellent pigmentation, after several trials and process adjustments.

Twin Screw Extruder

1️⃣   The Initial Challenge

We started with a standard extrusion setup and adjusted the 3 mm die by reducing the number of holes. While pellet size and uniformity were good, the major issue remained:

 Pellets were sinking instead of floating.

We quickly realized that simply controlling pellet size is not enough — floatability depends heavily on:

• Die hole configuration
• Pressure build-up inside the barrel
• Moisture absorption
• Density control

Too many die holes reduced pressure buildup, resulting in insufficient expansion and sinking pellets. Each pellet size (0.8 mm, 1 mm, 2 mm, 3 mm) requires a different die configuration.

2️⃣   Understanding Density & Floatability

Our investigation focused on the relationship between bulk density and floating behavior.

Bulk density = weight (grams) contained in 1 liter of feed.

Typical values:

• Floating pellets: 450–550 g/dm³
• Sinking pellets: above 550–600 g/dm³

During our trials, the feed density measured:

 557 g/dm³ — slightly above the floating threshold.

This explained why pellets appeared good visually but still sank in water.

3️⃣   Moisture Trials — Finding the Right Balance

To solve the issue, we conducted multiple R&D trials using different moisture levels in the flour/dough:

• 30%
• 32%
• 34%
• 37%
• 40%
• 45%

These experiments were performed with:

• 3 mm die configuration
• Barrel Zone 3 = 120 °C
• Barrel Zone 4 = 150 °C
• Adjusted screw speeds between trials

The key learning:

There is no single fixed moisture percentage — it depends on formulation, process setup, and final product target.

4️⃣   Initial Formulation Used

Our starting feed formulation included:

• Corn flour
• Wheat flour
• Soy
• Silkworm meal
• Shrimp meal
• Fish meal
• Bran
• Oilseed cake
• Rice DDGS

Each ingredient influences starch behavior, protein interaction, and expansion characteristics.

5️⃣   The Most Important Lesson — Moisture Absorption

Moisture percentage alone does not guarantee success.

The critical factor is:

 Whether starch granules actually absorb the water.

If water is:

• Added too late
• Poorly mixed
• Insufficiently absorbed

Then:

• Starch remains crystalline
• Gelatinization becomes incomplete
• Expansion decreases
• Pellets become dense and sink

We used a halogen-based moisture analyzer (≈ $1000+) to accurately measure moisture before extrusion.

6️⃣   What Gelatinization Really Means

In twin-screw extrusion, gelatinization occurs when starch granules:

• Absorb water
• Swell
• Break structure
• Become digestible

This happens only when three elements work together:

 Water (moisture)
 Heat
 Shear energy (from screw action)

Without proper moisture absorption, heat alone cannot cook the feed properly.

7️⃣   How Moisture Changes Product Behavior

~30–32% Moisture

• High shear
• Strong expansion
• Ideal for floating feed
• Risk of overload or burning

~34–36% Moisture

• Balanced cooking
• Stable extrusion
• Good gelatinization
• Most stable operating window

~38–40% Moisture

• Reduced expansion
• Softer melt
• Semi-floating applications

~45% Moisture

• Very low shear
• Minimal expansion
• Used for specialized products

8️⃣   Why “Absorption” Matters More Than Moisture %

Two plants may run at the same moisture level but achieve different results depending on:

 Same moisture % does not guarantee the same outcome.

9️⃣   Practical Operator Checks

Signs of good gelatinization:

 Glossy plastic dough
 Uniform expansion
 Strong floating ability
 No raw flour smell

Signs of poor gelatinization:

 Powdery melt
 Pellet cracking
 Hard core
 Excess fines after drying

 Process Equipment Adjustments

Once moisture was optimized, we adjusted parameters using the VFD (Variable Frequency Drive) and control panel of the twin-screw extruder.

Barrel Heating Zones

PID temperature controllers regulate barrel heating:

• PV = Actual temperature
• SV = Set temperature

These zones directly influence cooking and gelatinization.

Ammeter Monitoring

Analog meters track motor or heater current:

• Detect overload
• Monitor stability
• Prevent equipment failure

VFD Speed Controllers

VFDs control motor frequency and RPM:

• Main screw speed → affects shear and cooking
• Cutter speed → controls pellet length
• Feeder speed → controls feed rate

Fine adjustments were made using rotary knobs to stabilize product density and expansion.

1️⃣1️⃣   Unexpected Problem Discovered

During troubleshooting we found:

 Heater sensor installation was incorrect in Zone 3 & Zone 4.

This caused unstable heating and process inconsistency. Once corrected, extrusion performance improved significantly.

 Final Outcome

After optimizing:

• Die hole configuration
• Moisture absorption
• Temperature zoning
• Screw speed
• Feed rate

We achieved:

 Stable extrusion process
 Uniform 3 mm pellets
 Excellent pigmentation
 Proper expansion
 Reliable floatability

 Key Takeaway

Floating fish feed does not depend only on how much water is added — it depends on how much water the starch actually absorbs before exiting the die.

Mastering this principle transformed our product from sinking pellets into high-quality floating feed.