Thermal Processing

In-Container Sterilization & Pasteurizing

In all food manufacturing, the safety of the product is non-negotiable. Long shelf-life products in cans, pouches, jars, bottles, cups, trays, and cartons are thermally processed to ensure safety. The amount of heat required to achieve commercial sterility is dependent on many of the product features.

To achieve the high temperatures required for sterilization these products are processed in retorts. Retorts (also referred to as autoclaves) are pressure vessels that use the temperature pressure thermodynamic relationship to process food at temperatures above 100°C. The way that bacteria and their spores die, is a

Thermal Processing

logarithmic function of the amount of heat that they are exposed to; the higher the temperature, the faster they will die. It is therefore desirable to carry out the thermal process at the highest temperature the quality of the product can allow. Processing in modern well-designed retorts allows strict temperature and time control for exceptional product quality and confidence of safety.

There are two main temperature categories used in thermal processing: sterilization and pasteurization.

Products that are sterilized require critical heat treatment and are processed between 110°C and 135°C. These products have a pH of > 4.6 and are referred to as low acid. This low acid group has to undergo a more severe heat treatment as the process must be able to kill the spores of heat-resistant groups of pathogenic and spoilage bacteria such as Clostridium and Bacillus.

Products that are pasteurized need a milder heat treatment and are processed between 80°C and 105°C. They have a pH of 4.6 or below and are either naturally acid or acidified. This group can be pasteurized as the thermal process only needs to kill viable microorganisms, as the low pH restricts the germination of spores.


Retorts for batch sterilization

H.G. Molenaar has three different models of retorts namely static (steam/air), full water immersion with cage rotation and super heated water spray. The static retorts are manufactured in either vertical or horizontal configuration. Carbon steel or stainless steel construction is possible. Trolleys are used to load the baskets into horizontal retorts. Gantry systems are usually employed for loading baskets in vertical retorts.

View Brochure
View Video

Tunnels for In-Container Pasteurization

Tunnels can be only used for Heating or Cooling, or in combination with Heating & Cooling.

It may be necessary to warm a carbonated beverage after (cold) filling, to Cool a product after hot filling, or to follow a carefully designed heating & cooling curve to achieve specific Pasteurization Units (PU’s).

Our Pasteurization tunnels are designed for each container to follow a precisely calculated Time & Temperature Curve. Separate sections shower the containers with high volumes of cascading water at pre-determined temperatures, enabling us to reliably and accurately achieve the desired PU’s.

The continuous nature of tunnels enables us to save energy by swapping the heat recovered from outgoing products with colder incoming containers, thus saving energy requirements for both heating & cooling.

For temperature sensitive products, we offer either our very effective PU-Limiting option, or alternatively a more sophisticated PU-Control system.

View Brochure