Sour or bitter cup? How to adjust grind and brew time for 100% Kona

You made a cup of 100% Kona and something is off. Before you blame the bag, taste it again and ask one question: is it sour, or is it bitter? Those are opposite problems, and they have opposite fixes.

Sour and bitter are two different problems

Sour is sharp, thin and a little pinched at the sides of the tongue. It usually means the water did not pull enough out of the coffee. That is under-extraction.

Bitter is harsh, dry and lingers at the back. It usually means the water pulled too much out. That is over-extraction.

Kona is a mild coffee, so it shows both faults clearly. A heavy dark roast can hide a little bitterness. A mild Kona usually cannot.

Start from the same card every time

You cannot fix a cup if every cup is made differently. Start from the house card:

About 1:16 coffee to water by weight.
Water at about 200°F.
Fresh beans ground on a burr grinder right before you brew.

Make a cup that way, taste it, and only then adjust.

If the cup is sour

You want more extraction. Try these, in this order:

Grind a little finer. Smaller pieces give up flavor faster.
Brew a little longer. On a French press, that is a longer steep. On a pour-over, a finer grind will slow the pour on its own.
Check the water is hot enough. Water well under about 200°F pulls less out. A cool auto drip machine is a common cause.

Light roasts are the most likely to come out sour. See what roast levels mean. If you are brewing a light roast, start with a finer grind first.

If the cup is bitter

You want less extraction. Try these, in this order:

Grind a little coarser. Bigger pieces give up flavor more slowly.
Brew a little shorter. Shorten the steep, or pour off the press soon after you plunge so the coffee is not sitting on the grounds.
Do not squeeze the grounds. Pressing hard on a French press plunger or squeezing a cold brew filter pushes harsh flavors through.

If it is sour and bitter at once

That combination usually points to the grinder, not the recipe. A blade grinder makes dust and boulders. The dust over-extracts and goes bitter. The boulders under-extract and go sour. In the cup, you get both.

Changing the brew time will not fix that. A burr grinder will. See grinder and gear.

Change one thing at a time

Move the grind one small step, or change the time a little, and taste again. If you change grind, time and ratio all at once, you will not know which one fixed it.

Example (made-up cups, for illustration):

Cup A, medium roast, French press: tastes sour. Grind one step finer, same everything else. Next cup tastes rounder. Keep that setting.
Cup B, same bag, pour-over: tastes bitter and dry. Grind one step coarser. Next cup is softer. Keep that setting.

Write down the setting that worked for each brewer. They will not be the same.

When it is not the brew

Some flat or off cups are not an extraction problem at all:

Stale coffee tastes flat and papery, not sour or bitter. See how to store opened Kona and roast date vs best by.
A blend will not taste like 100% Kona, however you brew it. Check the bag says "100% Kona Coffee." See Kona vs blend.
A dirty brewer adds stale, bitter flavors. Clean it before you change your grind.

The short version

Sour: grind finer or brew longer. Bitter: grind coarser or brew shorter. Both at once: fix the grinder. Start from 1:16 at about 200°F and change one thing at a time.

FAQ

Is sour Kona a sign of a bad bag?: Not usually. Most of the time it is under-extraction. Try a finer grind before you give up on the bag.
Should I use more coffee if the cup is weak?: Weak and sour are different. Weak is watery: try a little more coffee at the same grind. Sour is sharp: grind finer first.
Does a darker roast fix sourness?: It can hide it, but it changes the coffee. Try a finer grind on the roast you bought first.
Do these fixes work for cold brew?: The direction is the same: coarser or shorter for harsh, finer or longer for thin. Cold brew has its own recipe. See how to make Kona cold brew.