Stoves of that era commonly burned charcoal as well as wood. These stoves had flat tops and the heat was concentrated on one side of the stove top so that cooks could cook things at different temperatures based on where the pot or pan was located. This was called the "piano" system. After coal was replaced with gas, French chefs continued to prefer the smooth cooking surface and so the majority of French gas stoves had flat metal surfaces over the gas burners, which continues to be known as the "French style" today.