In a lot of Asian households, an electric cooker keeps rice warm for hours, maybe even all day, chowsue notes on Chowhound. This makes it easy to scoop a bowl of steaming rice anytime somebody wants a snack, but is it safe? Is a rice cooker's keep-warm setting high enough to keep harmful bacteria from growing?
Anecdotal evidence suggests there's nothing to worry about. Many people (chowsue's husband included) grew up eating rice kept warm all day without being killed by bacterial poisoning. The danger zone for bacterial growth is between 40 and 140 degrees Fahrenheit (4 and 60 degrees Celsius), Chemicalkinetics says, so if a rice cooker is keeping the rice above the danger zone for 12 or even 20 hours at a time, it should be safe. Problem is, the keep-warm setting of many new rice cookers is lower than older ones. Chemicalkinetics suggests paying careful attention to your machine's specs to avoid bacterial danger.