High Pressure, Great Performance

Industrial Cooking Kettles are among the fundamental equipment in food processing [1]. These enable heat treatment of a broad array of food products at elevated temperatures and pressures. Food, beverage and dairy sectors utilize them for cooking and mixing [2]. Available in multiple sizes, large food factories find them as useful as small restaurants [3].

High pressure inside cooking kettles delivers distinct advantages. It boosts the safety and shelf life of food products while retaining nutrients and minimizing energy costs [4]. That apart, high pressure shortens cooking times, imparts better odor and taste to the food product, and maintains its catchy appearance [5]. 

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Applications

Cooking kettles are utilized to:

• Cook, Stew, or Mix Foods.
• Lower Liquid Content in Foods.
• Pasteurize or Sterilize Foods.

Pressure cooking via kettles makes delicious sauces by dissolving caramelized and mallaird-ized products back into the main stock [2]. Baby foods, ketchups, marmalades, chutneys, confectionaries, custards, jams, gravies, syrups, pet food, aseptic fruits, mayonnaise, preserves, and fruit jellies can all be produced by cooking kettles [2].

These are best suited for preparing and stewing meat, legumes, vegetables, and cereals [5]. Rice, pasta, beans, stew, sauces, gravy, soup, desserts, and stocks – all are cooked [6]. Cooking kettles also simmer or slow boil beans, stocks, and soups to lower their liquid content [6].

Types and Operation

Most cooking kettles include one vessel inside another vessel. The vacant space between the two vessels is the steam jacket, into which steam is directed. Steam condenses and releases heat to the walls of the inner vessel. The inner vessel houses the food products which receive this heat from condensing steam via conduction [7].   

Cooking kettles also operate the other way round. When ice water or cold water is circulated through the steam jacket, they cool down warm or hot foods. In this reverse mode, they work to mix cold salads [7].

Types of cooking kettles based on the energy source are:

• Direct Steam Kettles: use steam directly from a boiler and pass it through the jacket [8]. Steam condenses into water and is drained out as more steam is introduced [7].

• Self Contained Kettles: have a closed jacket containing distilled water. An electric or gas boiler mounted on the kettle stand converts jacket water into steam [8]. The condensed steam is not drained but re-heated into steam for continued heating [7]. Gas steam kettles are larger than electric steam ones [8].

Both types are available in the tilting or stationary type. The former can rotate about a horizontal axis allowing the pouring out of the finished food product. Stationary types have a sanitary drain valve to remove the prepared foodstuffs.

Here are general design and operational guidelines for steam kettles:

• Direct Steam Kettles:
  • Flow control valve and pressure lowering valve are important devices on the boiler-to-kettle piping [7].
  • Steam loses pressure while flowing through the pipe as also at every fitting and bend in the pipe. Insulated pipes minimize pressure drop [7].
  • Perform boiler size calculations at the kettle side to factor in all these pressure drops [7].
  • These kettles need a steam trap, which prevents steam from escaping with drain water [7].
• Self Contained Kettles:
  • Come with temperature control, pressure gauge, and distilled water mixed with corrosion inhibitor and anti-freeze solution [7].
  • Safety valve prevents excessive jacket pressure and enables distilled water replenishment [7].
• Steam Traps must be 2-3 times larger than the condensate flow rate warrants [9]. Recommended types for [9]:
  • Fixed/Stationary Kettles: inverted bucket type, thermostatic, and float-and-thermostatic.
  • Tilting Kettles: inverted bucket trap and differential condensate controller.
• One trap per kettle avoids short circuit [9].
• Returning condensate to boiler improves efficiency [9].
• Install one pressure relief valve each at the boiler and kettle end with pressure settings respectively below the rated ones for boiler and kettle [9].
• Before operating the kettle, check [6]:
  • Latches which are often clogged with sticky foods.
  • Compound Gauge must read “green zone,” not “vent air zone.”
• Remove air from jacket before turning steam on. Air lowers steam condensation rate. Position air vents at maximum distance from steam entry points. Choose steam traps that can vent out air [9].

Merits

Direct steam kettles cook faster, are more efficient, and possess greater capacity than self contained kettles [6]. Plus, they are cheaper and simpler [8]. However, self contained kettles are easier to maintain and more flexible for they can integrate with gas or electric supply [8]. Large food processing plants with boilers prefer direct steam kettles while small food factories go for self contained kettles [3].

Uniform heating of food is a very useful feature of all cooking kettles, direct steam or self contained. This is because the jacket surrounds a large part of the kettle. Steam jackets of most kettles engulf 2/3^rd of their surface area [6]. Fully jacketed kettles are also available [6].

Large jacketed area exposes greater surface area for heat transfer, thereby delivering uniform cooking with lesser energy and higher efficiency. Again, precise temperature control via the steam control valve avoids overcooking [2]. Temperature range differs and can be between 267 and 338⁰F [6]. Some operate from 212 to 300⁰F [10].

Mixer/agitator is another component that ensures uniform heating. Many mixers move the food vertically and horizontally for thorough blending. The mixer arms have scrappers at their ends to prevent food from sticking to the sides and burning [2]. Such burned food may obstruct heat conduction. Smooth internal surfaces also deter sticking.

Steam temperature rises with increasing steam jacket pressure [3]. Applying equal pressure from all directions (isostatic pressing) denatures proteins while eliminating microorganisms [4]. Denatured proteins are easily digested [11]. In short, isostatic pressing improves the safety, quality, and shelf life of food products. Maximum pressure rating of most cooking kettles runs from 35 to 50 psi [3], although 150psi is not unknown [12].

Load cells available with cooking kettles guarantee consistent quality production by providing an accurate weighing system [2]. Heat deflector shields safeguard personnel from heat-related burns [6].

Maintenance

Tell tale signs that a kettle needs replacement include:

• Longer cooking times
• Escalating repair costs
• Fissures and pitted surface on kettle walls

Here are a few maintenance tips that improve the service life and safety of the cooking kettle [6]:

• Regularly check and replace / top-up (if necessary) pressure relief valves, steam seals, water seals, screws, and distilled water (for self contained kettles).
• Lubricate bearings periodically.
• When cleaning:
  • Utilize non-caustic detergents, not chlorine-containing detergents.
  • Avoid abrasive cleaning tools such as steel brushes and scrapers.
  • Ensure the sprayed water does not touch gas or electrical parts.

Finally

In a way, cooking kettles are sophisticated versions of the humble pressure cooker. But their merits transcend the mere saving of cooking time and energy. It is precisely these advantages that explain their immense popularity.  

Cybernetik has been manufacturing equipment and delivering automation solutions for the Food, Pharma, and Agriculture sectors since decades. Contact us at +91 20 6790 9600 or [email protected] to experience the power of seasoned experience.

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References

1. Steam Jacketed Kettle, Gee Gee Foods & Packaging Co. Pvt. Ltd.
2. Product Batch Cooking Equipment, INOX Australia Pty Ltd.
3. Cornell Food Venture Center, Cornell University’s College of Agriculture and Life Sciences
4. High Pressure Equipment Designs for Food Processing Applications, Robert W. van den Berg, H. Hoogland, H. L. M. Lelieveld, Ludo Van Schepdael
5. Industrial Pressure Kettle VKP, Food Tech Process
6. When to replace Steam Jacketed Kettles, Foodservice Equipment & Supplies
7. North American Association of Food Equipment Manufacturers
8. The Best Soups, Broths, and Sauces: Your Ultimate Guide to Buying the Right Steam Kettle, GoFoodservice
9. Steam Kettle Hookup, Tim Bowser, Oklahoma State University.
10. Steam Jacketed Kettle FAQs, Zhucheng Honest Industry & Trade Co.,Ltd
11. Protein Denaturation, Archana Madpathi.
12. Steam Jacketed Cooking Kettles, DC Norris – North America