Yes, another's written content, whether found in hardcopy or online, is copyrighted--you may not use it. That is not to say that  you cannot use older recipes that are no longer copyrighted but instead are in the public domain (as a rough rule of thumb, content 75 years old or older is usually public domain--i.e. not copyrighted), but if you include any elements which are from another's newer version of the same recipe, that is copyright infringement. Example--and bear in mind I'm a non-cook, so if this doesn't make practical, real world sense, I apologize--say that a  "classic" hamburger recipe, dating back more than 75 years, is to include diced onions in the ground beef--you can publish that. Say that famous chef Fobby Blay has a version in a cookbook or website in which he includes diced scallions...if you copy Blay's recipe, you'd be infringing on his copyright.