Food warmers come in many shapes and sizes and are used for many different situations. The one thing they all have in common is that they hold food at safe temperatures for human consumption.
Heat lamps, hot boxes, steam tables, soup kettles and display warmers are just some types of food warmers that currently exist. Heat lamps, steam tables and soup kettles often leave food exposed in some way while they keep it warm. Hot boxes and display warmers fully enclose foods.
Electric- and Fire-Warmed
Of the types of food warmers listed above, most are electric. However, steam tables are usually warmed via small containers of gelled denatured alcohol (commonly referred to as Sterno). These are lit on fire and placed strategically in certain areas underneath the food chambers, and will keep them hot for hours.
According to the USDA's rules regarding food-safe temperatures, all cooked foods should be held at a minimum of 135 degrees Fahrenheit after cooking. Temperatures at or above this level have been scientifically proven to eliminate the growth of bacteria that cause foodborne illnesses.
Operator and Customer Safety
For operator and customer safety, the National Science Foundation (NSF) and the Underwriters Laboratories (UL) have established standards that govern commercial kitchen equipment. These should be adhered to when purchasing food warmers.
Advances in Technology
Standard food warmer technology has relied on heating the air surrounding food for years. When food warmers are enclosed, this can lead to heat loss when their doors are opened. Newer technologies as of January 2010 concentrate on heating the elements that hold the food (such as shelves) rather than the air surrounding it. This helps to avoid heat loss.