found this on the food standards website.
"What do I need to know about storing and reheating cooked rice and grains?
There are a few things to remember when reheating cooked rice and grains.
The spores of some food poisoning bugs like Bacillus cereus can survive cooking. If the cooked rice or grains are left standing at room temperature, the spores can germinate. The bacteria will multiply and produce toxins that can cause vomiting and diarrhoea. Reheating food will not get rid of the toxins.
It's best to serve rice and grains when they've just been cooked. If this is not possible, cool them within an hour after cooking and keep them refrigerated until reheating or using in a cold dish.
Rice and grains left at room temperature overnight should be thrown away.
Do not keep cooked rice and grains for longer than two days and do not reheat them more than once. Follow the manufacturers' 'use by' date for cold rice or grain salads."