Tray Drying
Tray drying is the oldest pharmaceutical drying method — wet material spread thinly on stainless trays inside a temperature-controlled cabinet. Slow, labour-intensive and uniformity-sensitive, but irreplaceable for products that cannot tolerate fluidisation or vacuum.
01What tray drying does
Wet cake, crystals or granules are spread on shallow stainless trays and loaded into a temperature-controlled oven with circulating air. Heat transfers by convection from the air and conduction from the tray surface; moisture diffuses through the bed and is carried out by the exhaust. The process is slow (typically 8–48 h) but predictable and very gentle.
- Inlet air temperature is the dominant CPP (typical 40–80 °C).
- Load depth controls drying time and uniformity (typically 25–50 mm).
- Air velocity across the trays drives mass transfer.
- Periodic turnover or raking improves uniformity at the cost of operator exposure.
- Endpoint usually LOD-based, sampled from multiple trays.
02Key parameters
| Parameter | Typical range | Why it matters |
|---|---|---|
| Inlet temperature | 40–80 °C | Heat-sensitivity vs drying rate |
| Load depth | 25–50 mm | Deeper = slower, less uniform |
| Air velocity | 0.5–2 m/s | Surface mass transfer |
| Turnover frequency | Per validation | Uniformity vs operator exposure |
| Drying time | 8–48 h | Process design |
03Execution and controls
- Load trays evenly — depth variation drives LOD variation.
- Verify oven temperature mapping annually with multi-point probes.
- Sample LOD from top/middle/bottom shelves and front/back trays.
- Use rack-position tracking to detect cold spots.
- Capture exhaust humidity if installed — an early endpoint indicator.
04Common mistakes
- Variable load depth tray-to-tray — LOD spread fails release.
- Single LOD sample from one tray — masking cold-spot wet zones.
- Skipping annual temperature mapping — silent drift across the oven.
- Operator turnover without documentation — losing reconstructable history.
- Using inlet setpoint as actual — no probe in the bed.
05Cross-industry examples
- API drying after crystallisation in API plants.
- Sticky herbal extracts in nutraceutical manufacturing.
- Friable granules where fluidisation breaks them.
- Veterinary intermediates with strict heat limits.
- Cosmetic powders where dust is a containment issue.
06How V5 Ultimate handles tray drying
Frequently asked questions
Q.Tray or fluid bed?+
Tray when product cannot tolerate fluidisation (too sticky, too friable, too hazardous to fluidise).
Q.How often map the oven?+
Annually plus after any HVAC or shelving change.
Q.Is turnover always needed?+
For deep loads yes; thin loads (<25 mm) may not need it.
Q.What's a typical drying time?+
8–48 h depending on product, load depth and inlet temperature.
Q.Can I run two products in one oven simultaneously?+
Only with cross-contamination risk assessment and physical segregation; usually avoided.
Primary sources
Further reading
V5 Ultimate ships with the Tray Drying controls already wired in — audit trail, e-signatures, validation evidence. Free trial, no credit card, onboard in days, not months.