Steam jacketed kettles and boiling pans — double-walled vessels that heat a batch through the jacket instead of the base, so stock, sauce and soup cook at volume without catching, with tilting and agitator models for easy emptying.
Heat enters through the jacket rather than the base, so sauce and stock don't catch and scorch. It also frees a burner and heats a far larger batch evenly.
Tilting empties by pouring, which matters once a batch is heavy enough that ladling it out is a two-person job. Fixed kettles suit smaller volumes and cost less.
Constant stirring — worth it for thick sauces, custards and anything that would need a cook standing over it. Thin stocks rarely justify one.
