How long past the expiration date can I use flavoured coffee syrup?

I just found a bottle of hazelnut flavoured coffee syrup in the back of the pantry. I can’t find the expiry date, but I’m pretty sure it’s been there a while (ie. possibly years). It smells and looks fine, and I want to put it in a cake so it will be cooked before it gets to anyone’s stomach. Also, it says that it is a pasteurised product. Do you think that it is safe?