I would certainly agree with procedural generated effects for ingredients, so the player experiments with different combinations doing "science", instead of following an online guide.
As for making it interesting, as stated before, it depends on the type of game. Now supposing alchemy has a large role in it i would suggest a system where ingredients have a combination of effects, some good, some bad, depending on what you want to get. So the player has to find what those effects are through experimentation, then find a way of isolating them through combinations.
i.e. you have a tree sap that can heal wounds, but also makes you slower, so you mix it with a bird bone powder that makes you faster to nullify that effect, however it also makes you weaker, then you add sulfur powder which makes you stronger but more vulnerable to fire. You can leave it there if you're not fighting fire using enemies.
Also you could make it so you dont get pure substances from nature, like a plant extract that is a combination of multiple pure substances, and then you would have to separate them with different methods depending on their properties, like filtration, decantation, distillation, etc.