Welcome to the Cake Decorators Q&A

I have seen a lot of cakes covered with ganache, and I always heard that if ingredients are make with Dairy it has to be kept cool and in the fridge. But I heard from another cake decorater that you should keep it in the fridge and you can leave it out. So what can I do , and how long can it stay out for

Hello Kimmerbearable

The type of ganache which is made in the tutorials is stable enough to be left out at a room temperature for several days under sugarpaste. The chemistry which occurs between chocolate and the high content of fat in the cream stablises the product. Use cream with a long use by date and keep ganache and ganache covered cakes wrapped in cling film to lessen risks from airborn bacteria.
To understand a little about the shelf life of ganache have a peek at my blog here: http://www.cakeflix.com/blog/the-shelf-life-of-ganache-by-madeitwithlove
Hope it helps.