How to Make Sausage Casing

The Manufacturing Process of Sausage Casing: A Scientific and Technical Analysis from Raw Materials to Finished Products

Abstract: Sausage casing, a key component in the field of food packaging, directly affects the shelf life, flavor, appearance, and food safety of sausages. This article aims to systematically and rigorously explain the entire manufacturing process of sausage casings, covering raw material selection, process technology, performance control, and industry trends, providing a professional technical reference for relevant practitioners.

Chapter 1: Overview of Sausage Casings and Core Functional Requirements

Sausage casing is not merely a simple wrapping material but a precise barrier system with multiple functions. Depending on the material and process, it can be mainly classified into the following categories:

Natural Casing: Derived from the digestive systems of animals such as pigs, cattle, and sheep, it offers good breathability, unique texture, and edibility. However, it has inconsistent specifications, limited strength, and higher costs.

Collagen Casing: Made from collagen sourced from cattle hide, pork skin, etc., it involves reconstructing the fibrous structure through chemical and physical methods. It combines some advantages of natural casings with uniform specifications, making it one of the mainstream choices in the modern sausage industry.

Cellulose Casing: Primarily composed of regenerated cellulose from cotton linter or wood pulp, it is divided into edible and inedible types. It features high strength, precise specifications, and adjustable breathability and moisture permeability, widely used in areas like high-temperature frankfurters.

Plastic Casing: Multilayer co-extruded films made from materials such as polyamide (PA), polyethylene (PE), and polyvinylidene chloride (PVDC). It offers excellent barrier properties, strong mechanical performance, and good printability, suitable for pre-packaged products requiring long shelf life.

Core Functional Requirements:

Barrier Properties: Effectively block oxygen (to prevent fat oxidation and aerobic bacterial growth), water vapor (to prevent product dehydration or moisture absorption), and light (to prevent photo-oxidation).

Mechanical Strength: Possess good burst strength, puncture resistance, and flexibility to adapt to high-speed filling, twisting, cooking, sterilization, and transportation processes.

Thermal Stability: Maintain dimensional stability during heat treatments such as cooking, smoking, and sterilization, without shrinking, melting, or delaminating.

Food Safety: All materials must comply with food contact material regulations (e.g., China's GB 4806 series standards, EU's EU 10/2011, etc.), and must not migrate harmful substances.

Processing Suitability: Offer good filling conformity, easy peelability (for some plastic casings), and excellent printability.

Chapter 2: Analysis of Core Manufacturing Processes

The manufacturing processes for different types of casings vary significantly. The following sections will focus on the manufacturing processes for collagen casings and multilayer co-extruded plastic casings, which account for the largest share in industrial production.

A. Manufacturing Process of Collagen Casing

Raw Material Pretreatment:

Sources: Mainly cattle hide corium or pork skin.

Processing: After strict veterinary inspection, raw materials are cleaned, degreased, and dehaired. They are then treated with alkaline substances like lime milk for liming to soften tissues, dissolve non-collagen proteins, and swell collagen fibers.

Collagen Extraction and Fibrillation:

Neutralize and swell the pretreated hides with acid (typically food-grade organic acids) to form a collagen slurry.

Mechanically shear and grind the collagen fiber bundles into a finer fibrous network, creating a uniform collagen paste. This step is crucial for determining casing strength and requires precise control of fiber length and dispersion.

Extrusion Molding and Curing:

Extrude the collagen slurry through an annular die onto a mandrel to form a tubular film.

The extruded wet casing is immediately immersed in a curing bath containing ammonia and aldehydes (e.g., glutaraldehyde). Ammonia adjusts the pH to promote collagen fiber contraction and cross-linking; aldehydes act as cross-linking agents, significantly enhancing the casing's heat resistance and mechanical strength.

Drying and Post-Treatment:

The cured casing enters a multi-stage drying tunnel, where it is gradually dehydrated under strictly controlled temperature and humidity conditions to prevent cracking.

After drying, it is humidified and pleated to impart flexibility and compressibility, facilitating subsequent shirring and packaging.

Finally, it undergoes cutting, shirring, packaging, and irradiation sterilization (e.g., Co-60 γ-ray or electron beam) to ensure product sterility and extend shelf life.

B. Manufacturing Process of Multilayer Co-extruded Plastic Casing

Raw Material Proportioning and Drying:

Select different types of polymer resins based on the required barrier properties, heat sealability, strength, etc., for the final product. A common structure is: PA/adhesive resin/PVDC/adhesive resin/PE.

PA (Polyamide): Provides excellent mechanical strength and puncture resistance.

PVDC (Polyvinylidene Chloride): Offers excellent oxygen and moisture barrier properties.

PE (Polyethylene): Provides good heat seal performance and inner-layer food safety.

Key Step: Hygroscopic resins like nylon must be thoroughly dried before co-extrusion to prevent bubble formation and hydrolytic degradation during processing.

Multilayer Co-extrusion Blow Film:

This is the core forming process. Different types of molten plastic resins are extruded through a precision extruder with an annular die.

The melt layers combine precisely inside or outside the die to form a multilayer bubble. The thickness of each layer can be precisely controlled by adjusting the screw speed and temperature of each extruder.

Cooling and Haul-Off:

The blown bubble is rapidly cooled and set by a cooling air ring, then flattened by upper haul-off rollers to form a double-layered flat film.

The entire process must be conducted in a clean room to control dust.

Corona Treatment and Winding:

Perform corona treatment on the film surface to increase its surface energy, improving adhesion for subsequent printing and lamination.

Finally, wind the film into large rolls for subsequent slitting, printing (if required), and bag making.

Chapter 3: Quality Control and Performance Testing

To ensure each batch of sausage casing meets standards, a strict quality control system must be implemented.

Physical Performance Testing:

Thickness and Uniformity: Measured using micrometers or online thickness gauges.

Tensile Strength and Elongation at Break: Determined with a universal material testing machine.

Burst Strength: Simulates filling pressure to test the casing's pressure resistance limit.

Oxygen Transmission Rate (OTR) and Water Vapor Transmission Rate (WVTR): Measured using specialized gas permeation instruments, these are core indicators for evaluating barrier properties.

Chemical and Microbiological Testing:

Migration Testing: Simulates components like fats, acids, and alcohols in sausages to detect any migration of harmful substances from the casing into the food.

Sensory Evaluation: Ensures the casing is free from off-odors.

Microbiological Limits: Test finished casings for total bacterial count, coliforms, etc., to ensure hygiene and safety.

Processing Suitability Testing:

Heat Seal Strength: For plastic casings, tests the strength of the seal.

Heat Shrinkage Rate: Measures dimensional changes of the casing under specific temperatures and times.

Filling Tests: Conducted on actual or simulated filling lines to evaluate filling efficiency, breakage rate, etc.

Chapter 4: Industry Development Trends and Outlook

Sustainability and Environmental Protection: Developing biodegradable casing materials (e.g., PLA-based materials) is an important future direction. Simultaneously, reducing energy and water consumption during production to achieve green manufacturing.

Functionalization and Smart Packaging: Incorporating active substances like antioxidants and antimicrobials into casings to actively extend food shelf life. Exploring smart packaging films with functions such as temperature indication and freshness indication.

High Performance and Low Cost: Using nanocomposite technology (e.g., nanoclay) to reduce the usage of expensive barrier materials like PVDC while maintaining performance, or developing new high-barrier polymers.

Customization and Digitalization: Providing customized solutions based on specific processes (e.g., low temperature, high temperature, smoking) of customers' sausage products. Utilizing Industry 4.0 technologies to achieve digital and intelligent control of production processes.

Conclusion

The manufacturing of sausage casings is a comprehensive technology integrating polymer chemistry, rheology, mechanical engineering, and food science. From the precise cross-linking of collagen to the精密 co-extrusion of multilayer polymers, each step demands high expertise and process control. As consumer demands for food safety, convenience, and environmental protection continue to rise, technological innovations in sausage casings will persistently drive the entire meat processing industry forward. For manufacturers, deeply understanding and mastering the core manufacturing principles is the cornerstone for ensuring product quality and enhancing market competitiveness.