Coffee can be bitter if you grind the wrong size for your machine. Sometimes it takes some tinkering. Overextraction will cause bitterness, which would be, if you ground too fine. Underextraction, it would be flavorless (too coarse). Getting it just right takes some time but a lot of times you alter this with your grind size and the roast is not actually to blame. If you think it's too bitter go coarser.
I use a pour over that actually prefers "sea salt size" coarse, and it really makes a difference. It was wayyy too fine before. Now I have the blend (local roasted) and grind down to perfection (you have to consider the combo, one size does not fit all).