The 4 types of Retort Steam-based processes are used for cooked and ready to eat packed food products sterilizing

Retorts utilize steam-based processes. 4 kinds of steam-based processes are used in sterilizing food, nutraceutical and pharmaceutical products. Steam goes in both formats as direct heating media (for example, saturated steam) or as indirect heating media (steam-heated water used in a water immersion process). The different types of retort processes are:

• Saturated Steam – direct heating through steam
• Water Immersion (rotary and static) – indirect heating through steam
• Water Spray (rotary and static) [Cascading water type is also included in this type] – indirect heating through steam
• Steam-Air (rotary and static) – direct heating through steam

As in all forms of design and engineering, each of the processes has advantages and shortcomings. Each has tradeoffs, and it is the objective of this blog to generally define the processes.

Picking the Optimum Retort Sterilization Process

Let’s be transparent about all the facts here: No retort sterilization process is the best! There is no such thing as one type (or size) fits all. It depends on the mere application. Retort sterilization processes should certainly be evaluated in the same way. Which is the best process for the application? And, which process is ideal for a particular container?

Let’s study each one of them in detail to figure that out:

1. Saturated Steam Retort Process

Trade-Offs Using the Saturated Steam Process

Pros

Low Capital investment required, particularly with carbon steel retorts

Convenient to operate manually

Can potentially process most canned products

Cons

Venting uses a lot of steam and is not an economically feasible step. Consumes a lot of energy.

Inflexible – typically rigid and limited to processing heavy sidewall containers, such as heavy cans.

Most fragile containers, such as pouches, plastic bottles, and plastic jars, cannot be processed.

With the overpressure process retorts gaining popularity due to the introduction of new types of containers requiring overpressure sterilization, the old steam retort is hard to beat for its low capital investment, along with the simplicity of design and operation. If one has a limited capital budget and the current and future product mix is limited to cans, then saturated steam retorts may be the ideal best decision.

2. The Water Immersion Retort (Static or Rotary)

The water immersion process is the most extensively preferred method of sterilizing products using an overpressure process. The water immersion process is quite similar to a saturated steam process in which the product is isolated from any influence of cooling air – the product is submerged in water. But, it is different from the saturated steam retort in which air is introduced into the vessel during sterilization.

Overpressure is provided by inducing air or steam on top of the water. In some instances, the air is added to the steam (which in turn heats the air). The heated air then agitates the water as it flows to the surface and in turn serves to pressurize the processing load.

The water immersion retort is versatile in its operation. Because it is an overpressure process, the machine can potentially handle most, if not all of the fragile containers.

The water immersion retort had, at one time, held a secondary position in popularity to the other types of overpressure retorts. However, in recent years, this machine has mounted a strong revival in popularity – particularly for all the products that needed a rotary process.

While the initial investment is much steeper(excessive) than the other retorts, it is the ideal machine for rotary processes.

3. The Water Spray Retort (Static or Rotary)

The saturated steam process is indeed one of the oldest methods of in-container sterilization. Since air is considered an insulating medium, saturating the retort vessel with steam is an essential requirement of the process. It is inherent in the process that the total amount of air would be evacuated from the retort by flooding the vessel with steam and allowing the air to escape through vent valves. There is no overpressure during the sterilization phases of this process since air is not allowed to enter the vessel at any time during any sterilization step.

However, there may be air-overpressure applied during the cooling procedures to prevent container deformation.

The water spray process is also an overpressure process, like water immersion, except that in this case the product is exposed to the influence of the overpressure air. It is quite similar to the saturated steam process in which; steam is the driving force for reaching the center of the packed load. But, the water spray process is different from saturated steam in which air is introduced into the vessel during sterilization.

Overpressure is then provided by inducing air (or steam) into the retort. To overcome the insulating effects of the air, the spray nozzles vaporize the steam and then mix the steam with the air. Some water spray retorts are also manufactured with a rotary option.

The water immersion retort is versatile in its operation. Because it is an overpressure process, the machine can potentially handle most, if not all of the fragile containers.

The water spray retort has become one of the most popular retort machines in the USA, primarily because it has the best ratio of flexibility to the investment enforced. The machines have a relatively simple design for an overpressure process and are an ideal buy for static processes. Low RPM rotary processes are also compatible with this machine, adding to its flexibility. (It should be noted that processes over 10 RPMs may experience increased “Come Up Times,” due to thermal distribution issues that may be inherent in the machine’s layout.

4. The Steam-Air Retort (Static or Rotary)

The Steam-Air process is also an overpressure process, like water immersion, except that in this case the product is exposed to the influence of the overpressure air. Because overpressure air enters the retort with steam, and steam is the only present heating medium, a large fan is used as a driving force to mix the steam with air, and to prevent cold spots in the machine. The fan is used in affiliation with a baffling arrangement inside of the retort to channel the heated steam-air mix to the center of the retort load.

Some Steam-Air retorts are also manufactured with a rotary option. The Steam-Air retort is versatile in its operation. Because it is an overpressure process, the machine can generally handle most, if not all of the fragile containers.

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