Why Temperature Still Matters After Salting of Hides and Skins

In the world of hide preservation, applying salt is only the beginning. The real challenge lies in managing the Curing Paradox: a high-stakes race between the stabilisation of the hide or skin and the inevitable onset of decay.

To win this race, you have to understand how temperature acts as the “referee” between your chemical treatment and the biological clock.

The Curing Paradox

The moment a hide or skin is flayed, a biological clock starts ticking. Preservation is a race between two primary processes, both of which are highly sensitive to temperature. If not managed correctly, the slower process (curing) will lose to the faster process (putrefaction).

1. Structural Stabilisation

This is a sophisticated chemical “shielding” process. While salt is the primary tool, modern curing is a complex system designed to lower Water Activity (a_w) and inhibit microbial life.

• The Osmotic Pump: Salt (NaCl) acts as a desiccant, drawing moisture out of the hide or skin structure through osmosis.

• The Chemical Cocktail: Salt is rarely used alone. It acts as a carrier for:

  • Bacteriostats and Fungicides (e.g., OIT): These provide targeted protection against a broad spectrum of microbes and moulds.

  • pH Modifiers (e.g., Citric Acid): By lowering the pH, we create an environment where most spoilage-causing bacteria simply cannot function.

• The Speed: This is a physical migration process. It is relatively slow because the chemicals must penetrate the interwoven network of collagen fibres to reach the “mid-point”, especially of the thicker and denser hide.

2. Putrefaction (Bacterial Spoilage)

This is the rapid breakdown of the hide or skin’s collagen (protein) structure by microorganisms naturally present on the skin.

• The Speed: In warm conditions, bacterial populations can double every 20 minutes.

• The Damage: If bacteria win the race to the centre of the hide or skin before the salt and biocides arrive, they digest the grain layer, leading to permanent “pitting,” hair or wool slip, and structural weakness in the final leather.

The Role of Temperature

Both the chemistry of the curing salt and the biology of the bacteria move faster in the heat. However, they do not accelerate at the same rate.

A Note on “Red Heat”

It is a common misconception that more salt fixes everything. Red Heat is a perfect example of why. Red Heat is caused by halophilic (salt-loving) bacteria. These specialised microbes actually thrive in saline environments.

Red Heat is usually a result of cross-contamination or the re-use of salt. Even in a salted hide, if the temperature remains too high for too long, these halophiles can proliferate, causing distinct reddish-pink discolorations and damaging the hide fibres.

Controlling the Environment

To resolve the Curing Paradox, you must manipulate the environment to favour your chemical system over the biological one:

1. Thermal Management: The single most important factor is to cool the hide or skin after flaying through washing, drenching and ice application, on removal from the carcase.

2. Curing Process: Apply the salt, pH modifiers and biocides as quickly as possible to minimise the bacteria’s “head start.” Hold in a cooler environment (ideally below 15°C) during the first 24 hours of curing.

3. The Result: Lowering the temperature marginally slows your salt penetration, but it drastically retards bacterial growth. This ensures your chemical shield reaches the full thickness of the hide or skin before any significant spoilage can occur.

Managing the interplay between temperature, salt saturation and biocide efficacy can be the difference between a premium export and a costly downgrade.

LASRA provide a full suite of tests for cured hides and skins, with recommendations for optimal curing.

Would you also like to learn more about our Salt Saturation Predictor Tool? Contact the LASRA team today.