Only NEW printers that have not been used with regular ink should be considered for edible ink printing.
The edible ink cartridges should be food contact safe, so buy from a reputable supplier. And the edible ink of course has to also be food grade. Here is a link to the ingredients for the InkEdibles brand of edible inks (
http://support.inkedibles.com/?qa=332/what-are-the-ingredients-for-inkedibles-edible-ink). These edible ink contain ethanol. Ethanol and other alcohols can resist the growth of microbes.
Whatever printer that you use for edible ink printing should be dedicated for edible ink use only (do not use regular ink). DO NOT MIX regular inks with edible inks. Never use edible ink with a cartridge or printer that has had regular ink running through it because contamination can occur.