What is the difference between Steam Infusion and direct steam injection?


One question we are always asked by food processors is how does steam infusion differ from direct steam injection. If you’re already using steam injection then the good news is steam infusion is a straight swap for your current system. We’ve broken the differences down into three sections:

  1. The introduction of Steam into the Product

  2. Heating Speed/Efficiency Compromise

  3. Processing Conditions

Introduction of Steam

The key difference between steam injection and steam infusion is the speed at which steam is introduced into the product and the resulting operating conditions.

Direct steam injection

Direct steam injection takes various forms either adding steam through apertures around the skin of the vessel or through a lance positioned inside the vessel. It involves discharging a series of steam bubbles into the product. Steam injectors are engineered to create a turbulent zone within the steam injector body to help mix the steam and product. This allows for slightly higher operating steam pressures than a rudimentary sparge pipe. One of the key challenges around efficiency is that steam bubbles can easily reach and break the surface, escaping to atmosphere.

Steam Infusion

In contrast, the Steam Infusion Vaction unit accelerates steam into the product at speeds reaching 1,000 m/s (3,280 ft/s) disrupting the product in the process. Special profiling within the Vaction unit steam chamber accelerates the velocity of the steam to above the speed of sound. As the steam passes into the mixing chamber through an annular nozzle, the steam disrupts the fluid flow and breaks it into small droplets, referred to as the vapour phase.

The small droplets within the low pressure vapour phase offer a significantly increased product surface area for the steam to condense into, resulting in a temperature gradient in the order of 12°C (54°F). This provides for no hot surface contact / hot spots preserving the quality of the product and eliminating Maillard reactions and caramelisation of certain sugars.

Cross Section showing the pressure drop and temperature increase across the Steam Infusion Vaction unit

As the steam condenses into the fluid droplets, the pressure rises. This is referred to as the condensation shock-wave and generates a pumping effect. The Steam Infusion Vaction unit pumps at a rate of up to 50,000 litres (13,208 US gal) per hour on water.

Heating speed/efficiency compromise 

Traditionally, when heating with direct steam injection there is a compromise between heating speed and efficiency. With Steam Infusion, food manufacturers can overcome this compromise as the disruptive processing environment decouples steam addition rate from inefficiency.

Steam injection

Steam injection relies on contact time between the steam and the product to condense into it. If the pressure were to be increased the contact time would be reduced as flow rates increase and steam could fail to fully condense remaining in a gaseous state and exiting the system as steam. This inefficiency will increase as the product temperature and temperature difference between the product and steam reduces. Steam injection, therefore, leads to an inversely proportional relationship between efficiency and heat up times as steam pressure is changed leading to compromises.

Steam Infusion

With the annular design of the Vaction™ Unit allowing steam to condense within the unit itself the heating process does not rely on contact time between the steam and the product and it has the ability to run at comparatively higher steam pressures without compromising on efficiency.

This makes the Steam Injection process very slow, uncontrollable and potentially varied. Whereas Steam Infusion’s complete retention of the steam means not only is it faster and more efficient, it is also easier to control.  


Processing conditions

The partial vacuum generated within the Steam Infusion Vaction unit described above offers food manufacturers different processing conditions to explore and develop products with.

No burn-on contamination

Cooking with Steam Infusion prevents exposure to excess temperature preventing Maillard and caramelising reactions.

High-speed cooking

Shortened cooking times preserve flavours and can increase the capacity of your cooking systems.

Flavour enhancement

The low-pressure vapour area within the Vaction unit assists in the transfer of flavours providing the opportunity to potentially reduce ingredient additions whilst still maintaining similar taste and mouth-feel for the products produced.

Particulate processing

The Vaction unit has a 47mm (1.85 in) uninhibited bore allowing particulates such as meat and vegetables to pass through undamaged.

Product matching aka act like a steam injector

By reducing the steam pressure to 2.0barg (28 psig), Steam Infusion acts like a steam injector making it easy to match products.