What is Commercial Sterilization? Process and Goals for Food Processing

The adjective “sterile” has multiple definitions–everything from geographic regions to intellectual quality. For our purposes, we will focus on perhaps the most common: ‘an environment devoid of living microorganisms, namely spoilage and pathogenic microorganisms.’

In most cases, sterility can be achieved by either chemical or physical means, or a combination of the two. 

What is commercial sterilization?

For food processing, commercial sterilization is a process designed to eliminate microorganisms, including bacteria and spores.

By reducing the microbial load, food manufacturers are able to prevent spoilage, in accordance with government and industry standards. This process guarantees a long shelf-life without refrigeration. 

What is the goal of commercial sterilization?

It is a critical safety measure to prevent foodborne illnesses. Strict adherence to processing parameters is required to ensure the product is ultimately safe for consumers, which is the end goal of commercial sterilization.

Commercial sterilization goals:

• Eliminate pathogens: Sterilization destroys dangerous microorganisms that can cause foodborne illnesses (such as Clostridium botulinum, which causes botulism) 
• Prevent spoilage: Sterilization inactivates microbes that cause food to spoil or develop off-flavors, textures, or odors to maintain product quality
• Inhibit toxin formation: Sterilization reduces the risk of toxins developing through fermentation, such as yeasts and molds that could grow and spoil the product
• Achieve commercial sterility: Commercial sterilization ensures that enough microorganisms are eliminated so the product can be safely stored under normal conditions at room temperature for an extended period (4+ months)

The survivors of the sterilization process are typically thermophilic spores–heat-loving bacteria that require temperatures much higher than normal storage conditions to grow. Since these foods are stored at room temperature or below, these surviving spores remain dormant and harmless.

How does commercial sterilization work?

Commercial sterilization is a multi-step process:

• First, packaged food is heated to a high temperature (typically between 110-121°C) in a high-pressure vessel called a retort, or autoclave
• Next, that temperature is held for a set amount of time to ensure the process is effective in destroying most microorganisms, including heat-resistant spores
• Finally, the product is cooled to prevent further cooking, maintain quality and taste, and ensure a stable product

While enough heat will completely sterilize food, too much heat will render food unpalatable or inedible. It is for this reason that commercial sterilization was developed.

Commercial sterilization destroys pathogenic and spoilage organisms that can grow in food under normal storage and handling conditions. This includes both vegetative (metabolically active growing and reproducing) cells and their non-vegetative (metabolically inactive) spores.

Some bacteria are genetically programmed to develop spores when conditions become too adverse for normal metabolism. The spore, by natural design, will remain dormant until conditions favorable to metabolism return. Because spores are quite resistant to heat, commercial sterilization occurs at the elevated temperatures of 121° C (250° F) or higher. 

Vegetative cells are killed at relatively milder temperatures of 87.8° to 100 °C (190° – 212° F). This is called pasteurization and is the method of rendering acidified foods shelf-stable.

What types of food need to be commercially sterilized?

Foods that require commercial sterilization include:

• Low-acid goods

• • Vegetables and beans
  • Soups and sauces
  • Meats, seafood, and poultry

• Acidic or acidified* foods with a pH** less than 4.6

• • Tomato-based products (canned tomatoes, salsa, and marinara)
  • Fruits and juices (lemon, orange, pineapple, apple)
  • Some dairy products (cheeses, yogurt)
  • Condiments (ketchup, soy sauce)
  • Other processed foods (processed snacks, fast food)  

• Other food products

• • Baby food
  • Pet food (canned of pouched)

* Acidified foods (pickles, relishes, salsa, hot sauce) are low-acid foods to which acids are added to lower the pH to 4.6 or less. Processing these foods means a combination of chemical (acid) and physical (heat) to kill microorganisms. 

** pH is a measure of acidity ranging from 0 to 14, 0 being the strongest acid and 14 being the opposite thereof, namely, basic or alkaline.  

Another attribute of shelf stable canned foods that determines processing requirements is water activity. The water in a food product that has been sealed into a container exists in two forms:

• Bound water: Bound water is either ionically bonded as water of hydration or bonded to cell structures and molecules. Bonded water has no bearing on biologically affected food stability. 
• Available water: The amount of free water, or water that is not bound to ions or otherwise, is water activity. It is this available water (a_w) that will support microbial activity.  Any foods with  a_w > .85 will support growth of pathogenic and spoilage microorganisms in foods meeting the pH criterium.

What is aseptic processing and how does it differ from commercial sterilization?

Aseptic processing is a method where a commercial product is sterilized separately, then filled into a pre-sterilized package within a sterile environment. On the other hand, commercial sterilization uses heat to destroy all microorganisms in a product after it has been packaged and sealed.

In aseptic processing, the product is not only sterilized separately but also with high-temperature-short-time methods like UHT (ultra-high temperature). Aseptic sterilization is ideal for products that cannot withstand the prolonged high heat of terminal sterilization, such as certain beverages or pharmaceuticals.