Recipes are most effectively protected by the law of trade secrets, rather than copyright or patents.
Well known secret recipes were KFC's Kentucky-Fried Chicken and McDonald's Big Mac Special Sauce.
However, the law of trade secrets will only protect a recipe if it remains secret. It will not protect the recipe if it is reverse-engineered.
If the recipe can be easily reverse-engineered, it may not constitute a real trade secret. In the US case of Vraiment Hospitality, LLC v. Binkowski, a recipe for a brownie contained one alleged secret ingredient, but that secret ingredient was relatively easy to recognise on tasting the brownie. According, the court held that the brownie recipe was not a trade secret.
Copyright will only protect the written form of a recipe, but not the substance of the recipe.
The Patents Act states that an application for a patent may be refused where it the alleged invention is: "a substance that is capable of being used as food, and is a mere mixture of known ingredients" or "a process producing a substance that is capable of being used as food by mere admixture" (see section 50(1)(b)).