The absolute best plain, bold, non bitter black coffee you will get is 1% Inawera Kawa (coffee) mixed in unflavored liquid (you can buy unflavored liquid in your nic ratio with your preferred pg/vg super cheap from most vendors). Closest premix to black coffee....925 by goodlifevapor....not even close in comparison.
I was extracting my own coffee prior to getting the Inawera flavor, tastes great - but it gunks
coils like nobody's business. The Inawera flavor is super clear and its just black coffee. Easy to mix if you buy premade unflavored liquid.
Good luck on the coffee quest - its not an easy flavor.