By Jake Norman *
Steam is often an important ingredient in the food processing industry. It can be the most effective and efficient cooking method in terms of transferring heat to your process when used correctly. Yet there are a number of decisions to be made in order to get the very best results. First up, it’s necessary to have culinary grade or clean steam on site to ensure your steam is free of contaminants and therefore safe to use in food products: will this be possible in your existing site? Then a choice needs to be made: what method of delivery is to be used? Steam injection or Steam Infusion?
Here, we take you through the pros and cons of both cooking methods and help to explain why more food companies are switching to Steam Infusion cooking.
What is Steam Injection?
Typical steam injection units are compact, inexpensive and simple to use. The process works by passing steam through the liquid to be cooked in a direct contact process. Steam injection relies on contact time between the steam and the product to condense into it.
Steam is injected into the fluid through a mesh or with a multiple nozzle arrangement, which creates a dispersal mechanism so the steam can pass through the fluid more effectively. This may also include a variable shutter to vary the number of orifices that the steam may pass through, allowing food manufacturers to regulate for changes in steam pressure and maintain entry velocity throughout the cooking process to standardise batch quality. In some cases, the design also incorporates spiral vanes, which effectively mix the fluid as the steam is injected, accelerating the entire production process by heating and mixing simultaneously.
What is Steam Infusion?
Steam Infusion is also a direct contact heating process, however in this method, steam condenses on the surface of a pumpable food product, gently yet rapidly heating a variety of food ingredients and products including milk, cream, soups and sauces.
The core operating principle of Steam Infusion is that of disruption, which is controllable, enabling standardised batch cooking time and time again. The disruption process creates a negative pressure condition to aid thermal and kinetic energy transfer to the fluid being processed. Special profiling in the form of an annular nozzle within the steam chamber accelerates the velocity of the steam to above the speed of sound to cause maximum disruption when it hits the liquid. As the steam passes into the mixing chamber, the steam disrupts the fluid flow and breaks it into small droplets, referred to as the vapour phase.
The diagram shows how the process creates an environment of vapourised product surrounded by high energy steam. This vapour provides a significant surface area for the steam to condense into as the pressure rises, heating the fluid extremely rapidly yet very gently as it is a uniform process, which is referred to as the condensation shock-wave. It generates a pumping effect, which can reach a rate of up to 50,000 liters per hour on water. In this way, Steam Infusion can heat, mix and pump products all with just one unit. What are the differences in terms of results?
There are a number of differences in the results achieved by the two cooking methods.
The key areas include: Speed of cook
The primary difference between steam injection and Steam Infusion is the speed at which steam is introduced into the product and the resulting operating conditions. One of the main reasons food manufacturers add direct steam injection to their cooking vessels is to speed up heating times. However, traditionally when heating with direct steam injection there is a compromise between heating speed and efficiency because of an inversely proportional relationship as steam pressure is changed. If the pressure is increased, the contact time is reduced as flow rates increase and steam fails to fully condense. In this scenario, it remains in a gaseous state and exits the system as steam; wasting energy and water, as well as slowing down the process. This inefficiency will increase as the temperature difference between the product and steam reduces and can also lead to increased variability within each batch as it’s hard to create consistency within the cooking process.
With Steam Infusion, food manufacturers can overcome this compromise as the disruptive processing environment decouples steam addition rate from efficiency due to the fact that Steam Infusion allows efficient heating at a higher steam flow rate. The disruptive way the steam is introduced means that all the steam is condensed into the product prior to leaving the pump, causing a rapid heat transfer and minimising energy wastage. In an experiment conducted at the University of Lincoln’s National Center for Food Manufacturing (NCFM), heating 1,000 liters of water from 20°C to 70°C took 26 minutes with steam injectors, while a single Steam Infusion Vaction™ unit heated the water in less than eight minutes.* The graph shows the difference in heating times with various steam heating methods.
With Steam Infusion, steam can reach the product at speeds reaching 1,000 m/s, which disrupts the product in the process. In this way, food products can be cooked, mixed and pumped within a single unit, often removing the need for multiple stages of processing to save time, a key advantage in the food processing industry where every second counts. These shortened cooking times also preserve flavours and can increase the capacity of your cooking systems, as well as ensuring consistency for every batch.
One of the key challenges with direct steam injection is the exposure of your product to high-temperature steam. This can result in fouling and discolouration of delicate sauces such as béchamel sauce. Also, when processing tomato based recipes, the product often turns orange as the tomatoes become over-processed.
Steam Infusion prevents exposure to excessive temperatures and the resulting Maillard reaction because of the partial vacuum generated by the unit as it heats, mixes and pumps products within the vessel. In this way, it’s possible to avoid this discolouration and create a product that’s much more attractive to consumers.
The supersonic steam flow entrains and vapourises the product flow to form a multiphase flow, which heats the suspended particles by surface conduction and condensation. This causes rapid and uniform heating over the unit in a temperature gradient in the order of 12°C, ensuring there are no hot surface contact or hot spots so manufacturers can preserve the quality of the product and eliminate Maillard reactions and caramelisation of certain sugars. This can be extremely useful, particularly from a development perspective, as products appear cleaner and are a better match to the concept sauce cooked in a traditional kitchen set-up. It also allow manufacturers to tap into the trend for ‘home-made’ style products as it’s easier to achieve this result with Steam Infusion.
Cleaning and downtime
Steam injection relies on complex mechanical assembly with multiple voids and surfaces, which leads to inherent cleaning challenges. Unfortunately, this means more downtime as there will need to be a clean after each batch. However, because the Steam Infusion Vaction pump has no moving parts, manufacturers benefit from near maintenance-free operation. The simplicity of the unit, just a single annular nozzle, means that it is an inherently clean design. This facilitates cleaning in place (CIP) when it’s necessary and because there is no risk of burn-on, the automated CIP or manual clean process is much quicker as burnt on product no longer needs to be removed. In addition, the lack of burn-on means it’s possible to perform more back to back cooks with a Steam Infusion system without the possibility of burnt contaminates appearing as flecks within the product.
Minimising plant downtime is priority for food manufacturers, many of whom are operating at full capacity. Steam injectors are normally installed in the vessel jacket leading to complex installation on retrofits and can mean significant downtime while the project is completed. The Steam Infusion lance is simpler as it can be mounted onto the vessel lid in vessels with inclined agitation, resulting in minimal downtime. There is virtually no maintenance involved in the operation of Steam Infusion units so you can keep running your operations without factoring in costly downtime.
Direct steam injection is a relatively simple process whereby you’re bubbling steam through a sauce. Naturally, it’s going to heat up your product quicker but there’s not much else going on. As Steam Infusion allows more control over the steam flow rate, it’s possible to change the operating characteristics of the Steam Infusion Vaction pump from a gentle introduction of steam to a disruptive high shearing process environment, which enables the improvement of the performance of certain ingredients. For example, with Steam Infusion, it’s possible to create a creamier mouthfeel under certain operating conditions, as a fat mimetic is created, which also allows fat to be reduced by 20 percent.
The low pressure vapour area within the Steam Infusion pump also assists in the transfer of flavours providing the opportunity to potentially reduce ingredient additions whilst still maintaining similar taste and mouthfeel for the products produced – spices in particular can be greatly enhanced so smaller quantities are required.
In addition, by reducing the steam pressure to two Bar, Steam Infusion acts like a steam injector making it easy to match products and allowing you to use both methods with one piece of equipment.
Full steam ahead with OAL
Steam Infusion technology has been around for over 15 years, and its potential in food production was catalysed by OAL with a £1 million UK government funded Innovate UK project, together with the University of Lincoln and a leading UK food manufacturer. The team investigated the operating parameters of Steam Infusion and perfected the use in a number of applications, including soups, sauces and dairy products. Food manufacturers can eliminate burn-on and Maillard reactions, reduce fat in dairy products by up to 20 percent and create a creamier mouthfeel while at the same time achieving reduced cleaning and cooking times and lowering energy consumption.
With a number of system integrators across the globe, and a test facility at the National Centre for Food Manufacturing (part of the University of Lincoln), food manufacturers can get on-the-ground support from experts in the field, and work with development chefs to tailor their products to achieve the unique benefits of processing with Steam Infusion.
Based on data from University of Lincoln, National Centre for Food Manufacturing “Steam Heating of Water” White paper 2015.
*The Author: Jake Norman is Head of Sales & Innovation at OAL, Peterborough, UK