Two basic methods of in-container sterilization are batch retort and continuous retort.
Batch retort sterilization has the greatest flexibility for different products and containers. It has the advantages of simple operation and low investment cost, making it the most widely used worldwide.
So, why choose a continuous retort sterilizer?
This article will help you understand the characteristics and advantages of continuous retorts from many aspects by comparing them with batch retorts.
Table of contents:
- Thermal process advantage
- Energy efficiency
- Layout
- Flexibility
- More “Gentle” to containers
- Labor cost and maintenance cost
- Automation & intelligent production
- Conclusion
1. Thermal process advantage
1) Batch retorts use huge cages as carriers. Each cage loads hundreds or more containers, closely spaced with small gaps. The outer containers surround the inner containers, which affects heat transfer.
The outer containers in the cage get heat penetration first, while the inner containers require more time to get sufficient heat; this leads to the following problems:
- The lag time for obtaining heat must be considered to ensure that the innermost products get sufficient heat treatment, so the overall heating time needs to be extended.
- Prolonged heating may cause the outer products to be burnt due to exposure to high temperatures for too long.
- Products in different positions in the cage receive heat for different amounts of time, which can cause them to taste inconsistent.
2) Continuous retort sterilizers use custom-made carriers to load containers. Each carrier only loads one or two rows of containers, and there is still a lot of space among carriers; this ensures that heat transfers smoothly.
After the carriers enter the sterilization vessel, instantaneous heat can penetrate each container. As the chain moves at a constant speed, the products in each carrier get the same heat treatment; this eliminates the master-slave heat transfer relationship that exists in batch retorts, bringing the following benefits:
- It shortens the overall heating time by saving the lag time for the inner containers to obtain enough heat.
- Because unnecessary additional heating time is saved, the problem of the product being burnt due to being exposed to high temperatures for too long is avoided.
- Because the products in each carrier get the same heat treatment, the problem of inconsistent taste is avoided.
3) For batch retort sterilizers, cages usually remain stationary in the vessel during sterilization. In the continuous sterilizer, carriers are transmitted by the chain and enter the sterilization vessel, moving from top to bottom layer by layer. As the layer switches, the carriers flip over simultaneously, stirring product inside the containers. In addition, the continuous sterilizer can also set the carriers to maintain 360℃ rotation during sterilization so that the products in the container are continuously agitated.
Thanks to this agitation, all parts of the product in the containers are evenly heated, further improving sterilization quality and ensuring consistent product taste. The agitation of the product also significantly accelerates heat penetration, shortening the required heating time.
2. Energy efficiency
Batch retort sterilizers process “one batch” of containers at a time. When processing each batch of containers, each sterilization vessel must repeat the loading, closing door, heating, sterilizing, cooling, opening door, and unloading cycle.
The entire process of the continuous sterilizer, including loading, sterilization, cooling, and unloading, is continuous. The temperature inside the sterilization vessel is always stable within the specified range. Coupled with the thermal process advantages explained in the first point, this saves a lot of steam, water, and electricity consumption in heating and cooling.
3. Layout
For large-quantity production, batch retort sterilizers must use multiple vessels for sterilization. In addition, various additional equipment is required to realize the loading and unloading process, including loaders, shuttles, unloaders, and cage transfer conveyors.
The continuous sterilizer contains the vessel for the sterilization process and a fully integrated loading and unloading system. The compact structure greatly saves floor space and is easy to install.
4. Flexibility
Both batch and continuous retorts can be used to sterilize various products and containers, including HDPE/PP bottles, bowls or trays, glass bottles, cans, plastic bags, etc.
Batch retort sterilizers can handle almost any container but may require a separate loading and unloading system. Continuous sterilizers are usually designed for containers of a similar shape and have the greatest advantage when dealing with high-volume production.
5. More “Gentle” to containers
In a batch retort sterilizer, containers are stacked layer by layer in the cages, and the containers at the lower layer of the cage have to withstand the weight of the upper containers.
In talking with many users of batch retorts, we often hear them complain about the deformation of the containers. To deal with this problem, some users have to make the containers stronger, for example, using more raw materials to make the plastic bottle thicker, which undoubtedly increases the manufacturing cost of the containers.
Each carrier of the continuous sterilizer only loads one or two rows of containers, so there is almost no container deformation problem. It also saves the additional manufacturing cost of dealing with the deformation of the container.
6. Labor cost and maintenance cost
A continuous retort sterilizer is a highly integrated sterilization system requiring only one person to operate.
Compared with batch retort sterilizers of the same production capacity, continuous sterilizers require less maintenance and fewer replacement parts.
7. Automation & intelligent production
More automated and smarter production lines are trends in food manufacturing. Due to its high integration and inherent “continuous” operation characteristics, the continuous sterilizer only requires simple system upgrades to adapt to future “unmanned workshops” needs.
8. Conclusion
There is no absolute superiority or inferiority between batch sterilization and continuous sterilization. When choosing between the two, we must consider more aspects such as our product characteristics, types of containers, and production capacity.
Suppose your production quantity is large and the containers are very similar, and you want to save energy consumption, labor costs, maintenance costs, and floor space as much as possible. In that case, a continuous sterilizer is undoubtedly the best choice.
If you have many different types or sizes of containers and the production quantity of each container is small, then a batch sterilizer is more suitable.