Burn taste in final spirit

[Adam78k]

So currently I have 7 spirit run's under my belt and I've noticed even after taking the heart cut from the run, which for me is usually between 75%-60% has a burn in the final taste, even after aging for 4-6 months plus. My current setup is a 15.5 gallon pot still in which I do 3, 10 gallon stripping runs for a final spirit run. From all the stripping run's I throw the foreshot's out and also take the first qt jar of all the stripping runs. Then comes the final spirit run which I run slow pencil led size stream.

I'm just currently trying to figure out why there is always a burn in my heart cut? Thanks guy's I appreciate the time.