Invented and patented by Surdry in 1983, the SWS retort process technology combines heating by direct steam injection with superheated water spray. With steam from the bottom and spray from top and sides, the result is uniform heat distribution in a short time.

A water-water plate heat exchanger cools the retort spray water, thus allowing the reuse of the cooling water via a cooling tower or a dry-cooler.

Compressed air is injected at any time to compensate for container thermal expansion.

When it comes to combining small cans in a large retort basket, saturated steam is the best way to achieve short come-up time in the slowest heating spot between cans. Higher steam consumption than SWS is the price to pay.

The counterpressure is limited to the saturated steam pressure, which limits the use to small rigid metal cans which can resist high internal pressure without deformation.

Cooling may be by spray or water immersion, with the backup of an optional heat exchanger for water recovery.

During cooling, compressed air is injected in a controlled way to keep up the pressure when steam condenses and so ensure container integrity.

This retort concept combines both SWS and SST technologies to provide the user the choice of both, especially when the basket is big and the use is intended for small cans as well as for glass or flexible containers which require counterpressure during heating.

The result is the retort with the highest flexibility for any container combined with the highest heating and cooling efficiency for each type of packaging.

The choice of the process technology is associated to each product recipe and the retort automatically sets itself for the selected process mode.

Surdry recommends the use of direct steam injection into the retort for process repeatability reasons with minimum maintenance, since a perforated tube is self-cleaning by the action of the steam, while a steam-water heat exchanger will often require cleaning to keep the critical heating time the same.

However, when steam is not available with the required quality, Surdry offers the choice of heating the spray water in an external heat exchanger.

WSH technology is offered with single or double heat exchanger, one for steam and a separate one for cooling, so that steam and water do not mix in the same unit.