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Commercial Sterility Processing

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Training participants will gain a basic understanding of Commercial Sterility Processing and its applications within food safety and quality systems. Basic knowledge competency will be verified through successful completion of the accompanying Commercial Sterility Processing assessment activity. Basic skill competency can be verified through the Commercial Sterility Processing competency checklist available as a resource for this training activity.

Key Definitions For Commercial Sterility Processing
- Anaerobic Environment: An environment in which there is no oxygen is present, Micro-organisms that live within this environment do not require oxygen for survival.
- Aseptic: Free from septic matter or disease-producing bacteria. In food processing and packaging, this is a word that describes the system used to package food in sterile manner.
- Bacterial Spores: A bacteria that, because of its thick outer wall, is easily able to survive in hostile environments otherwise not suitable for bacterial survival, growth and reproduction.
- Commercial Sterility: Commercial sterility means the absence of micro-organisms capable of growing in the food at normal non-refrigerated conditions at which the food is likely to be held during manufacture, distribution and storage.
- Continuous Flow Techniques: This is where food items, usually liquids, are heated rapidly and held at designated temperatures for a short time prior to being hot filled and sealed into their packaging.
- D-value or Decimal Reduction Time: The time in minutes required to secure inactivation of 90% of the target micro organisms under stated exposure condition.
- Hermetically Sealed: With a hermetic seal; so as to be airtight.
- Hot Fill: Containers are filled at high temperatures to ensure continued sterility of the container and product during and after the fill process.
- Incubation: Maintaining an item at the most favourable temperature for the growth of micro-organisms. Other environmental factor such as humidity and light exposure may also be controlled for optimum growth.
- Kill Step: A process step at which bacteria are killed. This is most commonly conducted by a process involving temperature and time.
- Log Reduction or Logarithmic Reduction: This is a measure of how effective a process step, such as time and temperature applications are in controlling the target micro-organism.
- Mercury In Glass or MIG Thermometer: A Mercury in Glass thermometer is an accurate vacuum sealed glass cased temperature measuring device often used for processes involving a retort.
- Microbiological Pathogens: Any microbiological entity including viruses, bacteria or other microorganisms that can cause food borne illness in humans.
- Pressure Vessel: A pressure vessel is a closed container designed to hold gases or liquids at a pressure substantially different from the ambient pressure.
- Retort: The application of time and temperature processing for sealed packaged items within a pressure vessel.
- Static Aseptic Techniques: This is where food items are filled at very high temperatures into packaging and sealed. The high temperature at which the product is filled will not permit bacterial growth as long as the package has not been opened. This process relies on a heat based kill step prior to packaging.
- Ultra Heat Treatment or UHT: UHT is achieved by a treatment involving a continuous flow of heat at a high temperature for a short time such that there are no viable microorganisms or spores capable of growing in the treated product when kept in an aseptic container at ambient temperature.
- Vegetative Bacteria: Bacteria that are in the growth and reproductive phase; not spores.
- Viscosity: Viscosity is a measure of the resistance of a fluid which is being deformed by either shear stress or tensile stress. For example, interpreting viscosity as thickness, water is thin and has a low viscosity; honey is thick and has a high viscosity.
- Z-value: The Z-value of a micro-organism is the temperature, in degrees Fahrenheit or degrees Celsius, which is required for the thermal destruction curve to move one log cycle.

Commercial Sterility Processing Development
When considering the development, documentation and implementation of Commercial Sterility Processing within food safety and quality management systems, the following information should be considered to ensure effective outcomes:

Commercial Sterility
Commercial sterility techniques have been used since the early 19th century to preserve foods. Early techniques involved sealing foods into glass bottles and boiling the bottles in water for extended timeframes. By the mid 19th Century, tin coated steel containers were being used in what would become one of the most prevalent food preservation techniques used throughout the world.

Commercial sterility techniques are perfect for preserving foods as they kill and deactivate micro-organisms and their spores through structured process controls involving the creation of an anaerobic environment and time and temperature treatments.

Micro-organisms, many of which are harmful to humans are also responsible for the spoilage of foods. Applying a suitable temperature to foods over a defined period of time breaks down proteins, which are essential components of living cells. This protein degradation kills vegetative bacteria, which is the easy part of the commercial sterility process. The challenge is to kill bacterial spores, which are more robust than vegetative bacteria. Bacterial spores are difficult to kill because they have thick protective walls which increase their resistance to heat, drying, freezing, chemicals and radiation. The ‘kill step’ for bacterial spores widely defines the modern parameters for Commercial Sterility.

Modern Commercial Sterility techniques include retorting, static aseptic and continuous flow applications:
- Retorting includes techniques such as canning and pouch retorting. This is where food items are hermetically sealed into appropriate packaging and subjected to specified controlled time and temperature too achieve Commercial Sterility;
- Static aseptic includes techniques such as hot fill packaging. This is where food items are filled at very high temperatures into packaging and sealed. The high temperature at which the product is filled will not permit bacterial growth as long as the package has not been opened. This process relies on a heat based kill step prior to packaging;
- Continuous flow includes techniques such as UHT. This is where food items, usually liquids, are heated rapidly and held at designated temperatures for a short time prior to being hot filled and sealed into their packaging.

The goal of all variants of Commercial Sterility is to produce foods that remain sterile whilst their packaging remains in-tact.

How does Commercial Sterility Work?
Commercial Sterility Processing relies on the application of one or more steps at which micro-organisms are killed and their spores destroyed. When applying a sterilisation procedure such as the application of heat, it is important to consider that not all bacterial spores are killed at the same time. A certain number of bacterial spores will be killed within any given period of time at a suitable heat, but not all of them.

This is where the most important factor of Commercial Sterility Processing comes to the forefront; the kill step is independent of the sterilization temperature, it is more reliant on time as a control mechanism.

The process through which time and temperature are used to kill bacteria is commonly known as the Logarithmic Reduction. Because logarithmic bacterial reduction can reach zero, it is never possible to guarantee absolute sterility. In this context, the efficiency of a sterilisation is expressed by the number of decimal reductions in the count of bacterial spores. The D-value, or Decimal Reduction Time is commonly used to indicate the killing rate of bacterial spores.

A D-value can be better explained as the specific time required at a specific temperature to kill, for example, 90% of bacterial spores, which is the same as reducing their number by one logarithm unit. In short; The D-value is a measure of heat resistance applied to a specified type of bacteria. It is important to consider that the D-value will be affected by, and is dependent on the species of bacterial spores involved.

The outcome of any heat sterilization process depends heavily on the following factors:
- The initial number of microorganisms in the items being subjected to the heat sterilization process;
- The D-value of relevant microorganisms;
- The Temperature of heat exposure;
- The Time of Temperature heat exposure.

In some Commercial Sterility processing applications, more than one temperature and time combination is applied to achieve the required product sterilization. This technique is increasingly utilised to maintain product quality aspects. In such instances, the required change in temperature is known as the Z-value. The Z-value is defined as the change in temperature required to alter the D-value by a factor of one logarithmic unit.

Commercial Sterility Sampling Procedures
As absolute sterility is not achievable, sampling plans with nominated acceptable tolerances are commonly defined for displaying conformance with the method of Commercial Sterility Processing employed.

A common example of a sampling plan applied for Commercial Sterility Processing is to apply a maximum acceptable defect rate of 1 per 10000 samples. In order to determine the effectiveness of the Commercial Sterility Processing methods employed, and to ensure the number of maximum defects does not exceed the nominated target, sampling procedures are implemented.

It is common for a defined sample percentage of finished products from each batch to undergo an ‘incubation’ process to ascertain the lack of micro-organisms within finished products. This basically supported the effectiveness of the time and temperature controls of each processed batch of product. Incubations are commonly conducted at 37 degrees Celsius or 99 degrees Fahrenheit, an ideal temperature for the growth of any potential micro-organisms contained within the processed product. Generally, if the products being incubated do not show any signs of bloating or vacuum, it is assumed that the Commercial Sterility process has been successful.

As the methods and techniques used for Commercial Sterility Processing are long established, and have a strong validated and verified history of achieving their intended food safety goals under controlled conditions, products are commonly not required to be microbiologically tested on a scheduled basis. Though the Commercial Sterility process should always achieve consistent results when conducted in a controlled and verified manner, it is important to consider that analytical microbiological testing can provide substantial evidence of product conformance to Commercial Sterility standards. In this context, it is of utmost importance for the analytical microbiological testing of Commercially Sterile products, when conducted, to ensure that the product within its original packaging is not contaminated as an element of the sampling or testing process.

Condition of Cans
Packaging Materials used in the canning process are made from a thin steel strip coated with a thin layer of tin on the internal and external surfaces. In many cases the interior of cans is lined with an organic compound to separate the food from the tin lining to prevent any chemical reaction. A rubber-like compound helps to form a hermetic seal when the bottom and lid are seamed onto the body of the can.

Once canned food is produced, poor transportation or storage practices might cause problems through denting or damage to the can seams. The leaks resulting from damage can allow contamination to enter the can which may allow spoilage to occur. Poor handling and storage conditions over time may also result in rusting of the outside of the can. Rusting commonly occurs when cans are stored in high humidity conditions, and is normally just unsightly, but can cause leakage over extended time periods.

Badly dented cans should not be used and should be drawn to the attention of the management of the store from where they were purchased. If the can ends are bulging, return the can unopened to the supplier as the contents might be contaminated. This may potentially indicate a significant risk to consumers. Cans that have stained labels may indicate poor storage practices and a possible leak; These should also be rejected if identified.

Using Canned Foods
The hermetically sealed contents of a canned food are uncontaminated prior to opening, so great care should be taken to ensure contaminants are not introduced when the can is opened. It is considered best practice for the top of the can to be opened to be washed prior to opening. This will ensure that any dust or dirt in the can top will not enter the food during the opening process.

When opening a canned food, a clean, sharp can opener should be used. Because the metals used in the construction of the can are relatively soft, the use of a blunt can opener can potentially introduce small pieces of metal into the food contained within the can. Blunt can openers also leave jagged edges which can provide health and safety risks. Can openers should ideally be washed after each use to further avoid the risk of contamination.

Once opened, canned foods should be treated as fresh foods. After opening, foods should be immediately removed from their can and placed into a non-reactive container with a tight fitting lid and stored within a refrigerator. Canned foods should be stored under refrigerated conditions and used within a suitable timeframe, as they will spoil after the hermetic seal on the can has been breached.

Aseptic Packaging
Aseptic processing and packaging is a complex technique as it relies on a minimum of three different sterilization techniques to be effective.

As elements of aseptic processing and packaging methods, sterilization is conducted:
- On the processing and packaging equipment prior to production;
- On the food product to be packaged;
- On the food contact surface of the packaging being used.

Failure of any one of these three techniques may result in an unsafe end product. In this context, the consideration of potential microbiological contamination points within an aseptic packaging facility must be addressed in a holistic sense.

For example, in a canning operation, if the product or package is contaminated prior to the retorting process, all bacteria and spores will be destroyed through the time and temperature process for the sealed can. A similar instance within aseptic packaging, where the product or packaging was not sanitary, would result in an unsafe product, as there are no further kill steps after the product has been packaged.

Flexible Commercially Sterile Packaging
Flexible packaging for commercially sterile food products are becoming increasingly popular due to their versatility and reduced processing times, which can be reduced dramatically compared to packaging such as cans. Additional advantages for manufacturers include reduced shipping costs and storage space for the empty flexible packaging, such as pouches. Whilst flexible commercially sterile packaging does have advantages in their application, challenges including seal integrity and more complex filling systems are required. Flexible commercially sterile packaging also requires significantly less heat than cans to achieve commercial sterility.

A typical commercially sterile pouch is a heat resistant bag made of laminated plastic films or foil, commonly consisting of an outer layer of polyester or nylon for printing, coding and protection, a middle aluminium foil layer that functions as the principal oxygen and water vapour barrier and an inner or food contact layer of a heat sealant material such as polypropylene. Products are filled aseptically and sealed, or sealed and sterilized by pressure cooking in a retort to produce commercially sterile finished products.

UHT Processing
There are two main modern UHT processing methods used within food industries. Both methods utilise heating, but the variants available include the application of direct and indirect heat to the product being treated. The method used relies on the quality and volume of the item being subjected to the UHT Process.

Direct heating usually involves subjecting the product to steam under controlled conditions until a nominated temperature is achieved for a nominated timeframe, after which the product is rapidly cooled within a vacuum vessel. The application of rapid heating and cooling gives a minimal sustained heat-load on the product, which results in a high quality end product.

Indirect heating involves the use of circulating the product undergoing UHT around partitions that are themselves heated or cooled according to the relevant process. Within this method, the heated or cooled medium on the non-product contact side of the partition transfers it heat or chill to the product undergoing the UHT process without physically contacting the product. The equipment used to heat the product within this method is also commonly referred to as a Heat Exchanger.

Heat exchangers are commonly available as three different types:
- Plate Heat Exchangers, which are commonly used for smooth liquids of low viscosity;
- Tubular Heat Exchangers, which can handle the treatment of smaller particulates and offer longer treatment times depending on the size of the tubes available;
- Scraped Surface Heat Exchangers, which are specially designed for the UHT of viscous products with or without particulates.

Cooling Process
Water is commonly used as an element of the initial cooling process for commercially sterile products. Any water sources used for product cooling must be chlorinated or treated in a manner that will not introduce potential microbiological pathogens into foods during the cooling process.

This is particularly important for canned products, as the nature of the metal used in construction of the can is prone to expansion and contraction during temperature and pressure variations. Potential contamination of foods within the can occur at the can seams or ends. If water sources used to cool retorted items are chlorinated and sterile, they will not contaminate the product inside the can. Water used for cooling processes for commercially sterile commonly contain at least 5 parts per million of free chlorine.

Additional cooling is commonly facilitated after the items have been removed from the retort within a well ventilated area.

If your food business supplies foodstuffs manufactured to a customer’s specifications, it is important to consider any specific Commercial Sterility Processing Development requirements in relation to their items.


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