Steam-jacketed kettles are very large, deep kettles mounted on a pedestal or legs to stand on the floor. They are used in institutional and industrial kitchens.
The bottom two-thirds of the kettle are covered by a metal jacket; shallow ones may be fully-jacketed.
There is a sealed air space left between the outside of the kettle, and its jacket, into which steam is pumped. The steam allows even heating and cooking of the food in the kettle from all sides. The steam pumped into the space never touches the food directly.
They will have safety valves to let off excess steam pressure.
On top, there is a hinged lid.
There is a faucet at the bottom to allow liquid to come out. Some steam-jacketed kettles can also be tilted, and have a spout on them for this. These are called “tilt kettles.”
Tilt ones can hold up to 80 gallons (300 litres), stationary ones from 10 to 150 gallons (4 to 570 litres). Small ones, 12 gallons (45 litres) or less, can be mounted on tables or counters.
Deeper ones are used for dishes such as beans, gravies, lentils, sauces, soups, pasta, puddings, and pie fillings, and can be used to make very large quantities of scrambled eggs.
Shallow ones are used for moist cooking of meat, and stews.
Full-training in their use for safety and maximum effectiveness is required. They require special cleaning procedures as well.
It is best to use distilled water as the water for the steam source, as tap water can cause mineral deposits on the heating coils, lowering their effectiveness.