Typical liquids for the bottling application are tar, varnish, resin, grease, chocolate or galantine.
There is no additional insulation so heat is lost by radiation into the surrounding air and the surface temperatures can be hot enough to burn unprotected hands.
Many viscous liquids and solids stored in steel drums require considerable energy input prior to removing from the container for processing.
These are available in various constructions using, induction heating, steam, or silicone heater mats inside a body with sufficient mechanical strength to support the weight of a full drum.
The magnetic field generated by the induction heater produces eddy currents in the drum wall, causing the steel to heat the contents.