Premix caking in high-humidity storage and enzyme loss during 95 C conditioning are two separate failure modes. Caking is driven by capillary condensation between particles; enzyme loss is driven by steam penetration into the carrier pore structure. A carrier needs a hydrophobic surface for the first problem and an intact mesoporous shield for the second.
Humidity and heat attack a carrier in two different ways
Tropical feed production exposes a premix to two stresses that most carrier specifications treat as one. High ambient humidity acts on the outside of the particle, while steam conditioning acts on the inside of the pore network. A carrier that solves one does not automatically solve the other.
Capillary condensation is the mechanism behind the first stress. Water vapour condenses in the narrow gaps between adjacent particles well below the dew point of the bulk air, because the curved meniscus in a narrow gap lowers the local vapour pressure required for condensation. Those liquid bridges then carry dissolved salts, and as the premix sits in storage the salts recrystallise and convert a reversible bridge into a solid neck. The result is the hard cake that blocks pneumatic lines and bridges in hoppers.
Surface energy governs whether those bridges form at all. The Silfeed HC Series carries a 110° hydrophobic barrier, meaning the water contact angle on the treated surface exceeds 90° and the surface is non-wetting. A non-wetting surface inverts the sign of the meniscus curvature, so condensation in the inter-particle gap requires a higher vapour pressure rather than a lower one. The Laplace pressure threshold for bridge formation rises accordingly, and this threshold is verified as a pass criterion on every batch.
Steam conditioning is a separate problem with a separate solution. During 95 C conditioning, steam penetrates the carrier and reaches the bio-active payload held inside the pore structure. Protection here depends on the geometry of the pore network rather than the surface chemistry. The Hexagonal Mesoporous Shield (HMS) architecture used in the HC Series raises the tortuosity factor of the diffusion path, so steam takes longer to reach the payload than the residence time of the conditioner. HMS pore integrity at 95 C is verified at at least 98% intact, and the shield stays active to a peak of 105 C.
Silfeed HC Series specifications
Three grades cover the range between flow stabilisation and thermal protection. Grade selection is driven by liquid load and by peak process temperature, not by species.
| Grade | Positioning | Oil absorption (g/100 g, ISO 787-5) | D50 (µm) | Primary function |
|---|---|---|---|---|
| HC-100 | Global flow standard | ≥ 280 | 10–15 | Universal flow stabilisation and microencapsulation in feed premixes |
| HC-200 | High-load adsorption | ≥ 320 | 5–8 | High-concentration essential oils and organic acid dry-powderisation |
| HC-Bio | Extreme thermal shield | — | — | Bio-active protection for extreme extrusion; shield active to 105 C |
Verification of these figures runs through the Silfeed laboratory chain rather than through supplier declaration alone. Surface mapping uses SEM on a Hitachi SU8010, thermal stability uses thermogravimetric analysis, and the reference report for the current HMS specification is UCSD-MB-2026-T22.
A four-step selection framework
Carrier selection becomes deterministic once the two stresses above are separated. Work through the steps in order, because a later step can override an earlier one.
Step 1 — Fix the liquid load first
Liquid load sets the floor on oil absorption. A target load below roughly 35% of carrier weight is served by HC-100 at an oil absorption of at least 280 g/100 g. Loads approaching 65%, which is the level demonstrated in production with essential oils, require HC-200 at at least 320 g/100 g. Selecting a carrier below the load requirement produces a powder that appears free-flowing at packing and releases oil in storage.
Step 2 — Check the peak process temperature
Peak temperature overrides the load decision when a bio-active is present. Any process reaching 95 C steam conditioning with enzymes or probiotics in the formulation moves the selection to HC-Bio, whose shield remains active to 105 C. Thermal exposure is the one criterion that cannot be compensated by increasing carrier dosage.
Step 3 — Match particle size to the mixing system
Particle size governs distribution in the mixer rather than capacity. HC-100 at D50 10–15 µm suits standard premix ribbon and paddle mixers. HC-200 at D50 5–8 µm gives the higher specific surface needed for high-load adsorption, and benefits from a longer dry-mix stage before liquid addition.
Step 4 — Verify against storage humidity, not ambient humidity
Storage conditions decide the caking outcome, and warehouse humidity in tropical markets frequently exceeds the figure quoted for the production floor. Specify against the 95% relative humidity condition under which the HC Series flow data was generated, rather than against an annual average.
Field results
Performance data below comes from high-output automated feed mills in North America, Europe and Southeast Asia, where the HC Series is in commercial use.
| Scenario | Condition | Result |
|---|---|---|
| Enzyme survival | 95 C automated conditioning, high-output poultry line | ≥ 88% activity recovery |
| High-load carrier | 65% liquid essential oils converted to powder matrix | Free-flowing stable matrix on HC-200 |
| Flow and OEE | Pneumatic dosing lines at 95% relative humidity | −30% downtime, 99.8% OEE |
| Formulation cost | Benchmarked against top-tier European suppliers | −8% to −12% net formulation saving |
Species requirements differ in which of these results matters most. Aqua formulations are judged on leaching prevention and water stability, dairy on rumen bypass and precision delivery, poultry on enzyme recovery and high-temperature integrity, swine on acidification and nutrient shielding, and pet food on palatability and lipid stabilisation.
Frequently asked questions
What causes premix caking at high relative humidity?
Premix caking in high-humidity storage is driven by capillary condensation. Water vapour condenses in the gaps between particles and forms liquid bridges, which then harden into solid necks as the premix sits in storage. A carrier with a hydrophobic surface raises the vapour pressure required for that condensation to start, which is why contact angle matters more than bulk moisture content.
How much liquid can a silica carrier hold before flow is lost?
Loading capacity tracks oil absorption. Silfeed HC-100 is specified at an oil absorption of at least 280 g/100 g, and HC-200 at least 320 g/100 g, measured by the ISO 787-5 method. In production, HC-200 has been used to convert 65% liquid essential oils into a free-flowing stable powder matrix.
Do enzymes survive 95 C steam conditioning on a silica carrier?
Enzyme survival depends on whether the carrier pore structure stays closed during conditioning. Silfeed HC Series retains at least 88% enzyme activity through 95 C steam conditioning, with HMS pore integrity verified at 95 C to be at least 98% intact. The shield remains active to a peak of 105 C.
Silfeed manufactures hydrophobic precipitated silica carriers at an ISO 9001 and FAMI-QS certified facility in Sanming, Fujian, with molecular engineering carried out in partnership with UCSD. Technical data sheets and samples are available at sales@silfeed.com.