Spec Check: Steam-Jacketed Kettles

Steam-jacketed kettles have been part of food preparation for more than a 100 years, with operators using this equipment to produce stocks, sauces, soups and fillings in large quantities. High-volume foodservice operations also use steam-jacketed kettles to efficiently rethermalize and hold food items until serving.

Governmental, institutional and commissary facilities often use large kettles along with pumps and vacuum bagging equipment in addition to a variety of different chilling methods, to produce thousands of prepackaged menu items at a central kitchen that staff can later ship to satellite facilities for use.

Along with faster cook times, steam-jacketed kettles offer a variety of other benefits during food preparation, such as a decreased chance of scorching and/or burning the food product due to lower temperature cooking. Steam-jacketed kettles can cook greater volumes of food with increased consistency. Using this equipment can reduce the need for labor since kettles require less monitoring during production compared with large pots on a range top.

The Cooking Process

Steam-jacketed kettles are stainless steel pressure vessels that utilize steam energy to transfer heat via conduction to the food product inside. The steam pressure determines the kettle's maximum temperature. The operating pressures of these kettles range from 45 psi to 50 psi, with the latter rating providing faster cooking at higher temperatures.

Cooking temperatures in these kettles range from a low of 150 degrees F up to 300 degrees F, and cooking times can vary from a few minutes to several hours, depending on the product.

Foodservice operators can choose from kettles constructed of either 304 or 316 stainless steel. While 304 stainless is suitable for general purpose use, such as boiling pasta or potatoes, 316 stainless offers increased durability so this type works best with more acidic foods, such as tomato sauce.

Operators can choose from one of three energy sources: electric, gas and direct steam. Direct-steam kettles work by plumbing in steam from a house boiler system. This method offers greater efficiency, cooking the fastest with the highest capacity in comparison to electric and gas models. The speed and design make direct-steam kettles a more common choice for use in larger hospitals and institutions. On the downside, direct-steam kettles require more maintenance, as the condensation in the supply line requires regular cleaning either manually or automatically.

Self-contained kettle systems tend to be more versatile, since this type better accommodates large or small kitchens with gas or electrical configurations. These units include a closed-steam system that runs from a gas or electric boiler in the kettle's stand. Although more expensive, these units' closed designs tend to make them easier for operators to maintain.

Although a less common option for foodservice operators, thermal fluid kettles offer higher cooking temperatures, up to 360 degrees F, for a wider range of cooking tasks.

When choosing a kettle, operators need to decide if a tilting or stationary type would work best in the operation. With tilting kettles, operators can choose from models with a handle, crank or motor that allow more efficient dispensing of the product by tipping the vessel. A pouring lip helps direct product neatly into its container. Some tilting models include a tangent draw-off valve to dispense product quickly. Operators often specify stationary kettles with a tangent draw-off valve to conveniently drain product from the vessel.

Not ordering a tangent draw-off valve on a stationary kettle when the application warrants it, represents one common mistake operators make when purchasing these units. If the order does not include a valve, some manufacturers will send a sign-off sheet to confirm this choice because it cannot be installed in the field. For operators cooking foods with larger food pieces, like stew, a 3-inch draw-off valve, which has a wider opening, is recommended.

The style and size of the kettle represent two other key specification considerations that relate directly to the unit's capacity. Stationary floor models typically offer capacities of 20 gallons and up, while tilting floor models accommodate 20 to 200 gallons.

Tabletop kettles, which come in gas, electric and direct steam variations, may be suitable for smaller volumes of between 1 quart and 12 gallons. These tend to be tilting type units.

If the foodservice operator plans to mount the kettle it is important to find a suitable location, such as a countertop, base, wall, cabinet or pedestal.

The majority of kettles are two-thirds jacketed, which means that the unit transfers its heat energy not only from the bottom of the kettle like in a stock pot on a range but also through the sides of the kettle. This increases the surface area for energy absorption into the product dramatically.

Selection Considerations

Operators need to verify whether the operation warrants a fully jacketed kettle, which provides more heat on the kettle's interior surface for faster cooking times. Fully insulated kettles also help keep the top rim temperature down, which prevents someone from burning their arms while stirring, and can be safer for inexperienced staff to operate.

Foodservice operators should also assess their future needs before selecting the size of their steam-jacketed kettle. This will allow the operation to better accommodate larger volumes if the business expands or the menu changes. Purchasing a kettle that does not leave the necessary space at the top to accommodate stirring, etc. is another common mistake. So most specifiers recommend erring on the side of caution and sizing up.

Here are several other key considerations:

  • Determine the products and batch sizes operators will cook in their steam-jacketed kettles. The applications will dictate whether a shallow or low height kettle is necessary. Occasionally, operators fail to take into account footprint limitations when specifying these units. Given the larger size of these units, it is important to allocate the proper space.
  • Confirm the floor drain and trough location, hood height and water availability for filling and cleaning when specifying these units. It's important to have available drains near the kettle, but this can be easy to overlook. Accessible drainage also is important for cleaning.
  • Understand the venting requirements. Considered light-duty equipment, kettles have the same hood requirements as typical steam equipment.
  • Measure the floor-to-hood height to verify that staff can completely raise the kettle for total access. If clearance is at a premium, shorter kettle models can save additional hood space. And shorter models' decreased height facilitates easier use and cleaning, since the kettle's interior is more accessible.

There are full and split lids available, and these should be chosen based on the kettle's application and menu.

While some kettle types utilize a power switch and pressure dial, others incorporate pressure sensors within the jacket or thermostats. Steam controls are typically a good idea to specify with direct-steam kettles to help control the heat intensity.

For operators with more inexperienced staff, heat deflector shields can be included to help avoid injury from hot steam.

Some of the common options operators should consider when specifying include spring assist and lift-off covers, gallon or liter markings, single- or double-pantry faucets, kettle fillers, pan carriers, draw-off valve hose kits, perforated strainers or solid discs for draw off, and mixing faucets.

A faucet option is a common afterthought that many operators neglect to consider when specifying. This addition, which mounts on the kettle, makes it easier for users to fill the vessel with water for boiling foods or to facilitate cleaning between uses.

Operators can choose from either etched gallon markings on the kettle's interior or a contour measuring stick that goes inside the unit to measure the amount of product.

When part of a cook-chill production line, kettles will include a cold water line connection option, which allows the unit to both cook and chill product, adding to its versatility.

Reinforced rolled rims add extra strength and damage resistance to the unit, while baskets for boiling can accommodate menus that include various types of pasta.

Foodservice operators can choose from a number of options specific to the size of the kettle. For example, larger kettles may offer a mixer arm option. This attachment allows easier stirring of the product during large batch cooking. Smaller countertop kettle options include floor stands with sliding drain pans or shelves.

New steam-jacketed kettle features include solid state temperature controls with self-diagnostic capabilities.

Most kettle advancements are in the area of ergonomic design, so operators should keep this in mind when choosing a model.


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