u/Confident-Durian-881

So I have a question I have two kinds of vanilla the cheap vanilla essence for cake to remove the egg smell and the expensive vanilla paste for cream Meringue, Custard and all but once I was using the cheap on in the Custard when cooked over the stove and it was so bitter ever since I only used the expensive one and not over and when cooking I add it at the end , yesterday i was making a Custard based cream and cooked with the vanilla and I was bitter but not as bitter as the cheap one how do I fix this and what the issue here