Is the Hot Filling Process Best for My Product Packaging?

Food manufacturers choose a hot filling process for their products because it offers an excellent balance between sanitation, product quality, and cost. However, this rapid heating and cooling process comes with some complications. The container itself needs to withstand the heat, and the labeling needs to work with containers that undergo major temperature changes.

So, when does a hot filling process make sense, and what changes do you need to make to your production system to create safe, reliably packaged products?

Table of Contents
What is Hot Filling and Where is it Used?

Benefits of Hot Filling

Choosing a Heat Resistant Container
Labeling Considerations: Temperature, Deformation, and Product Safety for Hot Liquid
Alternate Filling Technology Processes

Cold Fill Process

Aseptic Processing

Pasteurization

No Matter What You Make, We Have the Labeling Equipment You Need

What is Hot Filling and Where is it Used?

Hot filling is a process that uses heat to kill pathogens in food products and then uses the heat from that food to kill pathogens inside the container. Temperatures vary depending on the product, but the food is usually heated to between 194 and 204°F (degrees Fahrenheit) for a few seconds to sterilize the food and then cooled to between 179 and 185°F before packaging. Once the container is sealed, it’s cooled in a cooling tunnel for two or three minutes to reduce the product’s core temperature.

The containers may be pre-warmed to shorten the dwell time before cooling. This process is fast enough to prevent degradation while allowing enough time for heat to kill pathogens (plus it results in products that taste better and retain more vitamins and minerals than retort processing). Vitamin B, vitamin C, and potassium are the most susceptible to breakdown from overheating, making hot filling an ideal choice for vegetable and fruit juices.

Benefits of Hot Filling

So, what are the benefits of hot filling? For starters, an extended shelf life. The hot fill method makes a commercially sterile product, so you’re left with a longer shelf life — between 6 and 12 months. This varies depending on the food, as well as the barrier used to protect the food from contamination.

Common hot fill products include a variety of acidic liquid foods and beverages, including baby food, jams, jellies, fruit juices, vegetable juices, soups, marinades, and sports drinks. These products have a pH under 4.5, so they’re at least as acidic as a tomato. This acidity makes these foods an inhospitable environment for bacteria. Adding heat to the packaging process ensures any remaining microbes are killed off. Hot fill can’t be used for alcohol or carbonated beverages.

Even small changes to the process can cause major shifts in energy costs due to shifting heating and cooling demands. Due to the tight constraints on temperature and time for this process, backup systems are required to ensure the resulting products are safe when they reach consumers.

Choosing a Heat Resistant Container

While there are a variety of containers that work with the hot filling process, the market is dominated by glass, high-density polyethylene (HDPE) polyethylene terephthalate (PET), and polypropylene (PP). Of these, PET is the most popular choice. It’s great at handling high temperatures, and its low weight reduces shipping costs.

While there are some general guidelines for maximum hot fill temperatures, these maximums vary depending on the material formulation and wall thickness. For example, standard PET bottles deform when heated, and PP has a temperature limit of 165°F. Heat-treated PET bottles are typically rated for 185°F, while treated PP can be rated for temperatures as high as 205°F. In some cases, rapid cooling increases the maximum safe temperature for these containers.

Weight also needs to be considered. Glass bottles can withstand extreme temperatures, but are up to 40 times heavier than a plastic equivalent. High-temperature plastic bottles weigh up to twice as much as their standard equivalents. This is most noticeable with PET, which requires reinforcement around the body, neck, and cap to prevent collapse

Want to know more about these container choices outside of heat resistance? Learn more here with our blog, “Labeling Glass vs. Plastic Containers: What You Need to Know Before You Switch.”

Labeling Considerations: Temperature, Deformation, and Product Safety for Hot Liquid

Hot fill containers are still warm by the time they reach your labeling station, which can cause some issues with labeling. Thermal paper is usually stable up to 212°F, so it can be applied to hot-fill bottles without discoloring. Most adhesives work well at these temperatures, but you should consult your printer about possible issues. Adhesives wet out faster as temperatures increase, but too much heat decreases adhesion. Look for adhesives that have undergone a Shear Adhesion Failure Temperature (SAFT) test to understand what temperature causes adhesive failure.

It’s best to label containers after filling. While pre-fill labeling allows the adhesive to wet out on a room-temperature container, there’s always the risk that some of the product will spill onto the label during filling. Consideration also needs to be taken for temperature changes.

As the product cools, the container will contract. The label’s adhesive and face stock must be flexible enough to handle this change in shape. Most packaging suppliers include information on changes in diameter caused by temperature shifts for their hot-fill containers. Using this information, you can work with your printer to find the right face stock and adhesive for your application.

The inside of the container is only sterile as long as the lid is closed. To protect consumers, you can add a tamper-evident seal. If you’re using a hot filling process with beverage bottles, check out our vertical trunnion roller labeling system. It’s designed to let you add labelers as needed for your products, including a final stage for tamper-evident labels that stretch across the cap and neck of the bottle.

Alternate Filling Technology & Processes

Hot filling isn’t the only way to sterilize your food product and avoid spoilage before it hits the stores.

Cold Fill Process

Unlike the hot fill process, cold filling involves filling the container at room temperature without heating the product or container. It is commonly used for substances that cannot be subjected to high temperatures (including carbonated drinks, juices, and dairy products). In the beverage industry, exposure to high temperatures can alter the flavor, texture, and nutrients of the drink. While hot filling helps sterilize the bottle during the process, cold filling involves sanitizing the container beforehand.

Aseptic Processing

Aseptic processing is a method of food and beverage preservation that involves sterilizing the product and packaging separately and then filling the sterilized product into the sterile packaging under aseptic conditions. This process is designed to maintain the quality and safety of the product while extending its shelf life.

The aseptic processing method involves several steps:

1. 1. Sterilization: The product and packaging are sterilized separately using methods, such as heat, radiation, or chemicals. This ensures that there are no harmful microorganisms present in either the product or packaging.
   2. Aseptic Filling: The sterile product is then filled into the sterile packaging in a controlled and sterile environment, such as a clean room. This is typically done using specialized equipment that ensures the product and packaging remain sterile throughout the filling process.
   3. Sealing: The packaging is then sealed to prevent contamination and maintain the sterility of the product.

Aseptic processing is commonly used for a variety of food and beverage products, such as juices, milk, soups, sauces, and even baby food. The benefits of aseptic processing includes increased shelf life, reduced need for refrigeration, and preservation of the quality, taste, and nutritional value of the product.

Overall, aseptic processing is a highly controlled and sterile process that allows for the safe preservation of food and beverages without heat treatment or preservatives.

Pasteurization

Pasteurization is a filling technology used to increase the shelf life and safety of food and beverages by killing harmful microorganisms, such as bacteria and viruses. In pasteurization, the product is heated to a specific temperature for a certain amount of time, typically between 60°C to 100°C, depending on the type of product and the desired level of sterilization. This process can be done before or after filling the product into its packaging, depending on the specific requirements of the product and the filling process.

Pasteurization as a filling technology has many benefits, including the ability to extend the shelf life of products, reduce the risk of foodborne illness, and preserve the quality and nutritional value of the product. Pasteurization is commonly used in the dairy, juice, and beverage industries, as well as in the production of canned and bottled foods.

No Matter What You Make, We Have the Labeling Equipment You Need

Having trouble finding the right setup for your hot filling process? CTM Labeling Systems can help. Contact us, and we’ll get you in touch with one of our representatives who will work with you to find the right labeling equipment for your containers and production system.