I'm trying to train my tongue to recognize the 'bitter' taste of coffee, so I can improve my methods.
How can I achieve a bitter flavor with a French press?
This is a real question as I am not sure if it is heat, steep time, or the coffee grounds that produce the bitterness.
Bitterness comes from over-extracting the coffee. The factors affecting extraction are: water temperature, time, size of the grind, and to a lesser extent, agitation.
Using hotter water (above the usual 198F-202F), longer steep time, or a finer grind--or any combination of the three--will result in over-extraction, which will make the coffee more bitter. A darker roast will over-extract more easily as well, since an ideal extraction is typically 30-45 seconds shorter than a light roast.
I would recommend using the darkest/burntest roast you can find. Something along the lines of an Italian or Spanish roast if you can find it. Then, over extract the coffee as much as you possibly can by letting it steep much longer than normal. You should end up with a significantly bitter brew.
As Keith and Chris note - a darker (as in the darkest you can get) roast and boiling water is going to lead to a (in time, with experimentation, pleasant) over-extraction. Something else you can do is add a pinch of sea / kosher salt to the grinds prior to pouring in the water.
This will not make your coffee salty, it will simply bring out the natural bitterness of the extra compounds the over-extraction will produce. You can use a pinch of salt if you want to back off the temperature of the water, or how dark the roast is, in order to achieve basically the same effect as you would with either.
You have to experiment a bit, I use this method to get a more bitter / robust medium-roast Arabica quite frequently.
Also works wonders in drip coffee filters.
