@NP-3228. It depends on the chemicals used. This is herbal medicine, it is a lot more like cooking then modern medicine.
For example, this pie helps with the common cold and is a multivitamin. The bitter flavor in it is probably something to do with vitamin c (very sour in it's natural state), garlic (does help with the common cold but by itself can cause you to puke. Properly prepared garlic is smashed and cut up then left to sit 30 min before being comsumed. Eat it raw and on an empty stomach and you will puke), echinacea (kinda earthy/bitter? It is a little hard to describe homemade extract flavor of it. Best when put in tea to hide the flavor). Those 3 things can be cooked with and all will help boost your immunity.
I have noticed that people from Asia taste things a little different then western people. My fiancee says that pizza is sour? So the bitterness might tasted like something else like sour or pungent.
Source: I love to cook and have studied herbology and gardening and grow medicinal herbs (still a beginner tho)
Edit: the diet of city folk in ancient times was really poor. Scurvy was a thing because people would just live on stuff like bread. The fact he is making a fruit pie would save many people from an early death, even without the herbs. Few people understood the importance of food back then. The diet of a serf living outside of the city was much better and as such, they were fairly healthy. I think the average meal for a peasant was trout, black bread and some veggies with the occasional egg or foraged item. Deer were right out. The king owned all large animals on the land and to kill one was punishable by death