Keeper Niels Melchiorsen told the magazine Oekologisk Jordbrug (Ecological Agriculture): "For one reason or another, the tapirs and chimpanzees are choosing organically grown bananas over the others.
"Maybe they are able to instinctively tell the difference and their choice is not at all random," Mr Melchiorsen suggested.
"The chimpanzees are able to tell the difference between the organic and the regular fruit.
"If we give them organic and traditional bananas, they systematically choose the organic bananas, which they eat with the skin on.
"But they peel the traditional bananas before eating them," he added.
Copenhagen Zoo, which hopes to be awarded a "green label" as an environmental zoo, began feeding its animals at least 10 per cent organic products last year.
It hopes to raise the level to 15 per cent this year and reach 33 per cent in 2005.