What Kind, What Size and How Many Batch Retorts Do I Need?
So you have, or want to introduce, a containerized shelf-stable product to the consumer-packaged goods (CPG) market. Batch retort solutions offer the greatest range of technology and flexibility versus any other type of process solution that exists today. Here are some key considerations that will help guide you through the process of batch retort selection.
What Kind? The type of batch retort is determined by two main factors – the product and the container.
- Product characteristics will determine if a method of agitation will be beneficial or required. For instance, products that contain a dairy component will typically require agitation to prevent “burn-on,” which is the undesirable result of one or both of two reactions. The first is known as the Maillard reaction. This is a chemical process wherein certain sugars and amino acids react under high heat, thus forming a new chemical compound. The second reaction is caramelization, which is the pyrolysis of certain sugars. The high heat of commercial sterilization (±250°F/121°C) can also affect other ingredients in an undesirable manner. Agitation, also referred to as forced convection, is essentially stirring the product in the container. This reduces the time that a product needs to be subjected to high heat and offers two benefits – better product quality and higher throughput due to faster rates of heating and cooling. Conversely, some products benefit from a static process and long cook times to optimize product quality (i.e.: baked beans in heavy sauce). Other products, such as loafs, pâtés, and other high viscosity foods as well as products that are filled into the container with no headspace, do not benefit from agitation. These products undergo a different type of heating known as conductive heating (and cooling). Furthermore, the type of container can also play a role in determining what type of agitation is most appropriate to protect or enhance the quality of the product inside. The above product qualities will help determine if the optimum solution will need to be a static or agitating type retort.
- Characteristics of containers currently being used or planned to be processed in the retort in the future determine the type of process or processes the retort will need to perform. Steel cans, for example, also referred to as rigid containers, are structurally strong and can be processed with a saturated steam process without overpressure (also referred to as counterpressure). Overpressure is the additional pressure above the saturated steam table pressure (i.e.: 15 psig/1 bar = 250°F/121°C) that is required to appropriately protect the integrity of the container and its hermetic seal during the retort process. Glass jars and bottles, while also considered rigid containers, typically require an overpressure water immersion process for two reasons. Without overpressure, the closure or lid/cap may not maintain a hermetic seal as pressure builds up inside the container during the heating process. Secondly, if the glass containers are being agitated via end-over-end rotation, common in shelf stable low-acid ready-to-drink (RTD) beverage applications, the buoyancy created by the water inside the retort (known as the Archimedes’ Principle) helps to protect the fragile glass containers and reduces the clamping force needed to secure the load in the basket. This reduces the stress on the lid (i.e.: to minimize seal compound cut-thru) that could damage the hermetic seal. Semi- or non-rigid (i.e.: flexible) containers, such as pouches, and other polymeric containers such as plastic bowls, cups, trays, and bottles, require an overpressure type process. This prevents expansion of the container during heating, which can deform the container or damage the delicate seals and seams, thus impacting the integrity of the container. The above will help determine what type of retort process delivery solution is best for the application or variety of containers that may need to be processed in the retort. Overpressure retort processes include steam-air, water cascade, water spray, and water immersion.
What Size? Retort size or capacity is primarily determined by:
- Mandate time. This is the elapsed time allowed from when a container is hermetically sealed and when the retort process must commence. Mandate time is important for two primary reasons, the first being to prevent food spoilage before retort processing begins. Certain products, most wet pet foods for example, have high bacterial loads and can begin spoiling as quickly as 30 minutes after the container has been sealed. Mandate time also addresses another critical process factor, initial product temperature (IT). Product IT is a process parameter within the process filing, which is submitted to the FDA or USDA per federal regulations. Surpassing the mandate time may allow the product to cool below the IT, thus causing a process deviation. It is best to calculate the retort capacity, based on the upstream line speed, so that the retort can be completely loaded and the process started well within the required mandate time. If not, partially loading the retort will be necessary, which is not an efficient way to run a retort.
- Manual versus fully automated batch retort systems can also play a role in determining the size the of the retort that is best suited. For example, if baskets or tray stacks of containers will be manually delivered to and from the retorts, it is advisable to go with smaller diameter retorts, so the loads are more manageable and safe to move around by operators. It may require more retorts in such cases to meet the operational speeds that are expected. Automated batch retort systems (ABRS) can handle much heavier loads because all material handling is mechanized. Large diameter retorts can be used in these applications.
How Many? Determining how many retorts that are required in a batch retort system is primarily based on several factors as well.
- The above size determining factors of mandate time and the level of automation.
- The desired throughput or line speed is most commonly stated in containers per minute (CPM). In order to avoid the retort(s) being a throughput bottleneck, sufficient retort capacity is needed.
- Overall process duration. Batch retorts operate a series of steps during a process, including: loading, come-up to temperature, cook/hold, pressure and atmospheric cooling, and unloading. Typically, you want to maximize the size (i.e.: capacity = diameter x length) of the retorts to minimize the number of retorts needed, thus reducing the upfront capital expense for retorts and ancillaries, the installation costs, the future maintenance costs, and the floor space requirements.
We hope this short paper has been useful in helping you determine your batch retort equipment needs. For information on our retorts and retort room equipment, please visit our website www.allpax.com or contact us at email@example.com or via phone at (888) 893-9277 or (985) 893-9277.