Finally, the long-awaited bacon and ham are in hand, but when taking a bite, it is blocked by a thin layer of casing. Have you ever had a similar experience? So, what exactly is casing, and what are its types? How should we choose suitable casings when making different sausage products? Next, let's explore the mysteries of casings together.

As a packaging material for sausages, casings play an indispensable role in maintaining the quality of meat products and extending their shelf life. However, with the continuous increase in demand for casings, the natural casing market has gradually become in short supply, providing broad space for the rise of artificial casings. Currently, artificial casings on the market mainly include plastic casings, cellulose casings, and collagen casings. Each type of casing has its unique advantages but also faces some urgent problems to be solved.

1. Natural Casings

Natural casings are processed from the intestines of goats, sheep, pigs, and cattle. They have good smoke permeability, air permeability, and elasticity. They are not only edible but also suitable for smoking, drying, and steaming, and can give products an attractive color after smoking. Many delicious foods such as Harbin Hongchang sausage, Guangdong 腊肠 (Cantonese-style sausage), breakfast sausages, hot dogs, and Frankfurt sausages are carefully stuffed into these natural casings. However, natural casings also have some shortcomings, such as inconsistent specifications, poor mechanical adaptability, and an internal environment suitable for microbial growth, making them prone to contamination.

2. Plastic Casings

Plastic casings are typically made from high-barrier materials such as polyvinylidene chloride (PVDC), polyamide (PA), and ethylene-vinyl acetate copolymer resin (EVAL) composite flexible packaging materials. These casings are inedible but widely used for packaging meat products such as sausages, ham sausages, red sausages, pink sausages, sandwich sausages, garlic sausages, and minced meat sausages.

• PVDC Casings: They have advantages such as high gloss and transparency, low air and moisture permeability, oil and chemical resistance, and thermal shrinkage. They can be sterilized by heat steaming and remain unchanged at room temperature. The sterilization conditions can withstand high temperatures of 121°C, making them suitable for packaging high-temperature meat sausages, such as hams and sausages produced by high-frequency heat-sealing filling.
• PA (Nylon) Casings: There are three types: ordinary nylon casing film, shrinkable nylon casing film, and composite nylon casing film. Among them, shrinkable nylon casing film is particularly suitable for packaging low-temperature meat sausages, which can preserve the original flavor and more nutrients of the meat. Ordinary nylon casing film may produce wrinkles after packaging meat, affecting the appearance.
• EVAL Casings: Known for their excellent processability, high gas and odor barrier properties, solvent resistance, and being non-toxic and odorless. They are divided into shrinkable and non-shrinkable types. The former has good adhesion after heating and is suitable for packaging non-smoked sausages and steamed meat products; the latter is mainly used for packaging fresh meat and raw sausages that do not require heating.

3. Cellulose Casings

• Common Cellulose Casings: Made by directly blowing cellulose viscose, they have breathable and water-permeable properties, making them very suitable for smoking, and have excellent mechanical strength, ideal for high-speed automated production. These casings are inedible but can be directly filled, often used for making small-diameter sausages such as hot dogs and Frankfurt sausages.
• Fiber Casings: Processed by combining cellulose viscose with paper, they have high mechanical strength, smoke permeability without fat penetration. These casings are also inedible but can be smoked and printed, and naturally shrink during drying. They need to be soaked before use (printed products require longer soaking), and should be firmly filled with holes for air release. The surface of the casing should be completely dry before smoking to achieve uniform smoking color. After cooking, they can be cooled by spraying or water bath. These casings are suitable for making various cold-cut sausages, dry or semi-dry sausages, smoked sausages, cooked sausages, and loin hams.
• Fiber-Coated Casings: Made by pressing cellulose viscose with paper and coating the inner surface with a layer of polyvinylidene chloride, they have good barrier properties, effectively preventing product moisture loss and enhancing microbial protection. They have high shrinkage rate, a full and beautiful appearance, and can be printed. However, they cannot be smoked and are inedible. They need to be soaked in warm water before use, firmly filled during stuffing, steamed to the required core temperature, and then cooled by cold water spraying or water bath. These casings are suitable for making various steamed sausages without secondary packaging.

4. Collagen Casings

Collagen casings excel in smoke permeability, air permeability, and mechanical strength, with uniform specifications and various types. In terms of performance, they are quite similar to natural casings, not only easy to eat but also having good shrinkage and adhesion. More notably, they even surpass natural casings in resource stability and food safety. They can be evenly colored during smoking, making them highly suitable for mechanized production.

Before use, simply soak the collagen casings in warm water for about 10 minutes until fully rehydrated, then they can be filled. During filling, ensure firm stuffing. These casings are suitable for various smoking and steaming processes, with the maximum steaming temperature after drying and smoking controlled below 80°C. After steaming, they can be cooled by spraying or water bath.

Collagen casings are ideal for making Vienna sausages, breakfast sausages, hot dogs, and other various steamed sausages. Due to their integration of the advantages of both natural and artificial casings, collagen casings have attracted much attention in the market and have become the largest consumed casing product internationally.

Currently, collagen casings mainly use bovine collagen as raw material, but with technological advancements, by-products rich in collagen such as fish skin and fish scales have also been developed and utilized. Cross-linking technology has further improved their mechanical properties, barrier properties, and thermal stability. However, the production of animal collagen casings still faces challenges such as pollution and animal diseases. Therefore, research on casing film technology using natural plant proteins such as wheat gluten protein, soy protein isolate, or corn zein as raw materials is particularly important. Such technologies are not only expected to solve the above problems but also bring new development opportunities to the casing industry.