Packaging in the food manufacturing industry has two different purposes, which are containment and preservation. Containment is a logistical issue, whereas preservation is a scientific issue. When asking what is hermetic sealing, you need to know is a vital concept at the cross-section of shelf-life extension and food safety.

To manufacturers of powders, retorted foods, and beverages, the mechanics of a hermetic seal are not an option. It is the basic obstacle between a viable commercial product and a liability. This guide looks at the technical definitions, material requirements, and machinery processes that are needed to attain a real hermetic seal in an industrial setting.

What is Hermetic Sealing in the Food Industry

In consumer marketing, the term hermetic is commonly used interchangeably with airtight seal, whereas in industrial engineering and food science, the difference is important. The first step towards the right choice of packaging infrastructure is a clear understanding of this definition.

A plastic container with a snap-on lid seems to be closed to the average consumer since it contains water. This is an airtight seal. This is an airtight seal. It does not allow bulk movement of air and fluids. But, at the molecular level, airtight seals are usually permeable. Gas molecules may diffuse across the seal interface or the material over weeks or months, potentially leading to a slow leak.

By comparison, a hermetic seal (or gas-tight seal) forms a barrier that is not permeable to the interference of the external environment. It prevents the flow of gases (oxygen, nitrogen), water vapor, and microorganisms. An authentic hermetic closure keeps the internal environment of the package unchanged forever, irrespective of the changes in external humidity or pressure.

Engineers measure this integrity in two main measures:

• Tasa de transmisión de oxígeno (OTR): This is the rate of oxygen passage in 24 hours. In case of sensitive products such as milk powder, OTR should be close to zero.
• Water Vapor Transmission Rate (WVTR): This is a measure of moisture ingress. Large WVTR causes clumping of powders or staleness of dry foods.

Since dried spices to retorted meats are subjected to high temperatures to sterilize them, the industry standard is hermetic sealing to ensure that the product that comes out of the factory is the same product that comes to the consumer.

Why Hermetic Integrity Matters for Food Packaging

Investing in machinery that achieves a hermetic seal—such as a double seamer or an induction sealer—is a significant capital expenditure. The payback is, however, justified by the fact that it protects against biological and chemical degradation.

This is why hermetic integrity is not a bargaining point in the case of modern food lines:

• Prevention of Oxidative Rancidity: Oxygen is the main fat and oil enemy. Exposure results in quick oxidation, which gives rise to off flavors and rancid aromas, especially in nuts, fried snacks, and dairy powders. This chemical reaction is prevented by a hermetic seal.
• Nutrient Preservation: Sensitive nutrients such as Vitamin C and Vitamin A are destroyed when they come in contact with oxygen. Hermetic sealing is used to make sure that nutritional supplements and infant formulas retain the nutritional value that is stated on the label during their shelf life.
• Microbial Safety (Pathogen Control): In low-acid foods (pH > 4.6), the ingress of microbes, including Clostridium botulinum, is a critical safety control point. In canning, the seal helps to avoid contamination of post-process sterilization, ensuring total sterility.
• Moisture Control: It forms a total shield against humidity. This helps to avoid caking of dry powders and prevents crispy products not to getting soft, which maintains texture and freshness.
• Supply Chain Optimization: Long shelf life (12 months or longer) products enable manufacturers to access export markets without the need to use costly cold-chain logistics. It also minimizes the returns of retailers because of premature expiration due to mold or spoilage.

Common Materials and Technology Used for Hermetically Sealed Food

To obtain a hermetic seal, it is necessary to combine the appropriate barrier material with the appropriate sealing technology. Although the objective is the same, the process differs greatly between flexible and rigid packaging.

Materials in Hermetically Sealed Packaging

Flexible Packaging: This type consists of pouches, bags, and stick packs. They are based on multi-layer laminates (which may contain aluminum foil or metallized PET) to offer the barrier. The sealing process is nearly entirely Heat Sealing. The machine uses heat and pressure to fuse the inner layers of sealant (typically PE or PP) together. While standard adhesives are sometimes used in lamination, the seal itself relies on fusion. Although they are useful with snacks and lightweight products, flexible seals tend to be more susceptible to punctures and physical stress compared to rigid ones.

Rigid Packaging: Rigid packaging is the standard of choice when the product is of high value, heavy, or requires long-term durability. This consists of metal seals found on cans (tinplate or aluminum), glass jars, and rigid plastic containers.

• Latas de metal: These need Mechanical Interlocking (Double Seaming). The seal is created by physically deforming the metal of the lid and the can body. This is crucial for hermetically sealed cans and hermetic tins.
• Bottles/Jars: These often utilize Induction Sealing, where a foil liner is fused to the container lip.

Rigid packaging provides superior physical protection during transport and is often the only viable option for vacuum and nitrogen-flushed applications where pressure differentials would crush a flexible pouch.

Types of Sealing Techniques and Their Applications

The technique used determines the equipment that will be needed on the production line.

• Mechanical Double Seaming (Rigid Metal/Composite)
  • Required Machinery: Can Seamers (Seaming Machines).
  • Machine Variants: These include Semi-Automatic Seamers (where the operator inserts the can) in the case of boutique production and High-Speed Rotary Seamers (Multi-head systems) in the case of mass production.
  • Application: Canned foods, beverages, and industrial goods requiring structural rigidity and 100% hermetic integrity. This creates the classic hermetic can.
• Induction Cap Sealing (Rigid Plastic/Glass)
  • Required Machinery: Induction Cap Sealers.
  • Machine Variants: These are usually Inline Induction Systems that are mounted on a conveyor belt. They close bottles when they are undergoing high speeds. There are handheld models of lab testing or micro-production.
  • Application: Pharmaceuticals, peanut butter, dairy, and chemical bottles where leak prevention and tamper evidence are the most important.
• Vacuum and Nitrogen Flushing (Modified Atmosphere)
  • Required Machinery: Vacuum Can Seamers o Nitrogen Flushing Seaming Machines.
  • Machine Variants: These specialized seamers feature a closed chamber. The machine creates a vacuum and injects the inert nitrogen gas just before the process of the double seaming takes place.
  • Application: Infant formula, coffee powder, and nuts—products in which oxidation is a value-destroying process.
• Direct Heat Sealing (Flexible): It involves the use of heated jaws or wheels to fuse plastic layers. Although it cannot be applied to rigid cans, it is the standard for pouches.
  • Required Machinery: Vertical Form Fill Seal (VFFS) machines, Flow Wrappers, or Pouch Sealers.
  • Application: Potato chips, snack bars, and single-serve sachets.

The Mechanics of Hermetic Sealing for Metal Cans

In the case of canned goods manufacturers, such as tuna, infant formula, etc., the most important technical process in the factory is the double seam. Can sealing is based on physics (deformation) as opposed to heat sealing which is based on chemistry (melting). It is not dependent on glue or adhesive. It is based on the accurate bending of metal to form a labyrinth that is impossible to cross by bacteria or contaminants.

The machine that does this is the Can Seamer. It is necessary to understand how it works to control quality.

The Double Seaming Process Explained

A double seam is a hermetic seal formed by interlocking the edges of the can body and the can end (lid). It is a two-step procedure, which is performed by the rollers and chuck of the seamer.

The Anatomy of the Seam:

• Body Hook: The can cylinder flange is folded down.
• Cover Hook: The curled part of the lid is folded upwards under the body hook.
• Seaming Compound: A coating of rubber or latex on the inside of the curl of the lid. This acts as a compression seal; it is pressed when the metal hooks interlock to fill the microscopic spaces between the metal layers to make the seal gas-tight.

The Two-Step Operation:

1. First Operation (The Curl): The initial roller forces the curl of the lid beneath the flange of the can. It rolls the two metals loosely. The seam is made at this point but not tight. It looks rounded.
2. Second Operation (The Ironing): The second roller is used to press and tighten the seam with a lot of pressure. This compresses the compound and forces the body hook and cover hook to be in contact, creating a robust seal.

Common Seam Defects and Prevention

Since the process of double seaming depends on the precision of the machine, any minor errors in machine calibration may result in a seam defect. For hermetically sealed cans, even a microscopic gap is a failure.

The operator hardly causes these defects; the machine causes them. Poor quality seamers that have low tolerances or use soft materials like standard brass or copper in high-stress tooling areas (instead of hardened steel) may vibrate when in operation, resulting in uneven pressure. The answer is to employ high-precision can seamers with tooling that is stable and made of hardened grades of steel that do not change their settings during millions of cycles.

Achieving Hermetic Seals in Bottles and Jars

Cans are based on the deformation of metals, but rigid bottles (plastic and glass) have another challenge: the coefficient of thermal expansion. Glass and metal lids expand and contract at different rates under heat, which can loosen seals.

Another myth in the industry is that a tightly screwed cap is a hermetic seal. This is incorrect. The simple screw cap is based on torque- friction between the threads of the cap and the bottle neck. Nevertheless, plastic materials have a characteristic known as creep (cold flow), which implies that they creep under constant pressure. With time, or as the vibrations of transport take place, a screw cap becomes loosened in a microscopic manner. This punctures the seal, permitting air to pass. Thus, in the case of such products as peanut butter, pharmaceuticals, and condiments, Torque Capping is not a hermetic sealing technique. It is merely a closure method.

In order to have a real hermetic seal on a rigid bottle, manufacturers have to employ Induction Cap Sealing.

This technology forms a bond that is not dependent on the torque of the cap. It is done by using a specialized liner within the cap, which is made of a pulp board, wax, aluminum foil, and a polymer heat-seal layer. An electromagnetic field is produced as the capped bottle goes through an induction machine.

This field does not heat the plastic cap, but causes eddy currents in the aluminum foil layer. The foil becomes hot quickly, and the polymer film underneath it melts. This movie is directly fused to the land area (the lip) of the bottle. At the same time, the heat melts the wax, and the foil is released from the cap. Upon cooling the bottle, the foil is welded to the mouth of the container, forming a complete barrier to oxygen and moisture. This also gives evidence of tampering; the consumer has to physically open the seal to get the product.

Quality Control and Selecting the Right Sealing Machinery

To move on to production, it is necessary to choose the appropriate equipment and develop verification procedures. The equipment you select will dictate your throughput, your rejection rate, and your labor expenses.

Verification: Testing the Seal

You cannot assume a seal is hermetic; you must prove it. There are two main methods:

• Bubble Test (Destructive): Often referenced in ASTM D3078. The vacuum chamber is filled with water, and the sealed package is immersed in it. The pressure in the package is greater than that of the outside as the vacuum is pulled. In case of leakage, a stream of bubbles will come out. This is cheap and easy, but it kills the sample.
• Vacuum Decay (Non-Destructive): Utilizing standards like ASTM F2338. A sensor is used to check the pressure level in a chamber where the package is located. When the pressure varies (decreases) once the vacuum has been pulled, it means that the gas is escaping the package. This is accurate and suitable for high-value nutritionals or pharmaceuticals.

Machinery Selection Criteria

In line architecture consulting, we consider three aspects:

1. CPM (Cans/Containers Per Minute): Speed drives cost.
   1. A start-up may require a machine with 15-20 CPM.
   2. An established factory may require a rotary system with 50 or more CPM.
   3. Advice: Buy for your 3-year projection, not your current status.
2. Container Versatility: Do you seal one diameter of hermetic can only, or five? There are machines where the chuck and rolls can be changed quickly, and there are machines that are specific to one size. When you have a high-mix, low-volume list of SKUs, seek easy-changeover tooling.
3. Compatibilidad de materiales: PE bottles and PET bottles need different frequency settings to be inducted using an induction sealer. An aluminum can seamer needs roller pressures that are not the same as those of a tinplate hermetic can seamer.

Automation Levels

• Semiautomático: The operator puts the can in and switches on the cycle. Best suited to boutique brands, lab testing, or low-volume specialized runs. It is very flexible and is labor intensive.
• Totalmente automático: The product is fed by conveyors. The machine indexes, seals, and discharges automatically. This is necessary in scaling. Current automatic lines frequently incorporate nitrogen flushing and vacuum capabilities into the sealing station.

Ensuring Product Safety with Advanced Sealing Technology

Ultimately, the point of control that is most important in your production line is hermetic sealing. It is the final barrier between your product and the environment, ensuring it can withstand extreme conditions during shipping and storage. Failure in this case nullifies all the value added in sourcing, processing, and filling. Reliability is not a luxury; it is a working requirement.

This is the point at which it is a strategic benefit to collaborate with a specialized manufacturer.

Levapack has spent over 14 years refining the engineering behind can sealing and packaging automation. We don’t just sell standard units; we engineer solutions that fit specific factory footprints and production goals. Whether you are a small enterprise needing a robust semi-auto seamer or a large facility requiring a 40-can-per-minute nitrogen vacuum line, our equipment is built with premium components from Siemens and Schneider to ensure consistent, hermetic integrity. With a 16-month warranty and custom tooling capabilities, we help you secure your product quality and your brand reputation.

Do not risk your product integrity. If you are not sure what sealing technology is suitable for your container or production rate, contact a technical specialist now. Get in touch with us to negotiate a customized packaging that suits your needs in terms of shelf-life and safety.