Leather Manufacturing Series – Part 1: From Hide to Pre-Tanning
Estimated Reading time: ~9-10 minutes
Introduction: From Skin to Structure – Building on What Lies Beneath
In our previous blog, “Beneath the Surface: Unraveling the Anatomy and Biochemistry of Skin in Leather Manufacturing”, we dissected the dermis, epidermis, and collagen matrix at a molecular level. Now, Leather Manufacturing Series – Part 1 bridges theory to practice—showing how that living skin becomes a stable, clean substrate through the leather manufacturing process.
Pre-tanning (or beamhouse) operations are the unsung heroes of leather quality. From decay prevention to layer separation, every step ensures the hide is ready for tannin binding. Let’s walk the factory floor.
Sourcing and Preserving Raw Hides: Halting Decay at the Source
The leather manufacturing process begins at slaughter. Fresh hides—70% water, rich in proteins—are highly perishable. Bacterial enzymes can degrade collagen in hours without intervention.
Tanners source hides as meat byproducts, emphasizing traceability and sustainability. Preservation buys time until wet processing begins.
Key Curing Techniques
- Salting → 50% moisture loss via osmosis; global standard
- Drying → Sun-cured in arid zones; lightweight but humidity-sensitive
- Brining → Fast saltwater immersion for local transport
- Chemical → Bactericides in salt-scarce regions (use cautiously)
Pro Tip: Cure at 15–18°C. Flip salted hides every 12 hours to prevent “red heat” (bacterial bloom under salt crust).
Soaking: Reviving and Cleansing the Hide
Cured hides arrive stiff and crusted. Soaking rehydrates and cleanses—removing blood, dirt, and curing salts.
How It Works
- Equipment: Stainless steel paddle
- Water: 20–30°C, 300–500% float
- Chemicals: 0.1–0.2% wetting agent + sodium carbonate
- Duration: 6–24 hours, slow rotation
- Reputed Manufacturers: Olcina Group offers durable drums for soaking, built with resilient Bolondo wood or stainless steel for efficient processing .
Collagen swells ~20%, restoring flexibility.
Pro Tip: Add non-ionic surfactant to cut water use by 25%. Change bath if foam turns brown—sign of excess dirt.
Liming: Swelling the Collagen Matrix
Liming is the chemical opening of the hide—swelling fibers and loosening hair roots without fully removing hair.
The Chemistry
- Agents: Slaked lime (Ca(OH)₂) + sodium sulfide (Na₂S)
- pH: 12.0–13.0
- Duration: 18–36 hours in paddle vats
- Equipment: Paddle drums or vats for even exposure
- Effect: Collagen fibrils separate; hair follicles weaken at the root bulb
Pro Tip: Target pH 12.5 after 24 hours. Over-liming (>48h) embrittles fibers—test a corner hide for “slip” (hair pulls easily)
Unhairing: Mechanical Hair Removal
Unhairing is a separate mechanical operation post-liming. Hair is now chemically loosened but still attached—ready for removal without damaging the grain.
How It Works
- Method 1 – Machine Unhairing: Hides pass through unhairing machines with rubberized rollers and blunt blades. Pressure shears hair at the follicle base.
- Speed: 5–10 m/min
- Water spray: Washes hair away
- Method 2 – Manual Unhairing (small scale): Workers use dull knives on a beam to scrape hair off.
- Output: Clean grain surface + recoverable hair (for brushes, felt, or fertilizer)
Pro Tip: Adjust roller gap to hide thickness—too tight scores grain, too loose leaves stubble. Rinse immediately to prevent hair from re-adhering in alkaline residue.
Fleshing: Scraping Away the Underside
With the grain clean, the corium’s fleshy side is next. Fleshing removes fat, muscle, and connective tissue.
Precision in Action
- Machine: Cylinder flesher with helical blades
- Pressure: 2–4 bar
- Process: Hide fed under pressure; water cools and flushes debris
- Result: 10–20% weight loss, uniform thickness
- Reputed Manufacturers: Exeter Machine Company specializes in high-performance fleshing machines for hides, with options for remanufacturing .
Pro Tip: Start at lower pressure for thin hides. Check grain side after each pass—any shine means over-fleshing.
Splitting: Dividing for Diverse Destinies
Final pre-tanning step: splitting thick hides into layers.
Layering Expertise
- Machine: Band-knife splitter (laser-guided)
- Precision: ±0.1 mm
- Output:
- Grain layer → full-grain leather
- Flesh split → suede, bonded leather
Pro Tip: Mark grain side before splitting. Use flesh splits for small leather goods or dye tests.
Conclusion: The Foundation Is Set
Leather Manufacturing Series – Part 1 has transformed raw, biochemical skin into a clean, swollen, de-haired, de-fleshed, and layered substrate—primed for tanning.
From the collagen bundles we studied in “Beneath the Surface” to the beamhouse floor, every step preserves structure and prepares for permanence.
Next in Series: Leather Manufacturing Series – Part 2: Pre-Tanning Prep – Deliming, Bating & Pickling Continue to Part 2 →
