Although guinea pigs always appear ravenous, they do not eat to the point of gluttony; they feast only until they are full. Any uneaten food should be removed from the cage each day.
To avoid waste, feed a small handfull of fresh vegetables and fruit two or three times daily, preferably at regular once, rather than a large amount at once.
This will keep food fresh and clean, as well as prevent it from molding. Always wash foods before feeding them to your pet