How to tell which one you have

People mix these up constantly, and it is worth being sure before you start changing things.

Sour hits fast and hits the sides of your tongue. It makes you wince slightly, the way a lemon does. The cup feels thin and empty, and the taste disappears almost as soon as you swallow. If you find yourself wanting to add sugar to round it off, that is usually sourness.

Bitter arrives late and sits at the back of your throat. It dries your mouth out, a bit like over-steeped tea or burnt toast, and it hangs around long after the sip. If the first mouthful is fine but you do not want a second, that is usually bitterness.

If it is somehow both, you have an evenness problem rather than a timing one: water is finding a channel through the coffee bed and racing through part of it while barely touching the rest. Grind consistency and how you distribute the grounds before brewing are what fix that.

If it tastes sour, do these in order

You need to get more out of the coffee. Work down the list and stop when it tastes right.

• Grind finer. Smaller pieces mean more surface area and slower flow, so the water takes more with it. This is the biggest lever you have, by a long way.
• Brew longer. On espresso, aim for a longer shot time. On filter, a slower pour or a longer steep.
• Get the water hotter. Just off the boil, roughly 92 to 96 degrees. Water that is too cool is a very common cause of sourness and almost nobody checks it.
• Use more coffee. A bigger dose for the same amount of water gives you more to work with.

If it tastes bitter, do these in order

You need to take less out. Same list, opposite direction.

• Grind coarser. Bigger pieces, faster flow, less of the harsh end of the spectrum making it into the cup.
• Brew shorter. Cut the shot earlier, or stop the steep sooner.
• Drop the water temperature. Let the kettle sit 30 to 40 seconds off the boil. Boiling water scorches coffee and drags out bitterness on its own.
• Clean your gear. Old coffee oils go rancid and add a stale bitterness that no amount of dialling will fix. If it has been a while, this might be the whole problem.

What those numbers on a recipe card actually mean

Every bag of coffee we send out comes with a recipe on it, and it looks like this:

That is all a recipe is: how much coffee went in, how much drink came out, and how long it took. The ratio between the first two numbers is the useful part. 20 in and 44 out is roughly 1:2, which is a standard espresso. Push it to 1:3 and you get something longer and lighter. Pull it back to 1:1 and you get a short, syrupy ristretto.

Filter recipes work the same way with different numbers, because filter uses far more water per gram of coffee:

Here is the part worth understanding. The recipe does not include grind size, and that is not an oversight. Grind is the dial you turn to hit the recipe, because every grinder is different and no two are calibrated the same. If your 20 grams in gives you 44 grams out in 18 seconds, your grind is too coarse. If it takes 40 seconds, too fine. The numbers are the target and the grinder is the steering wheel.

So a recipe card is not a set of instructions to follow blindly. It is a description of what a good shot of that particular coffee looks like, so you know whether you have got there.

Change one thing at a time

The most common mistake once people start dialling in is changing three things at once, tasting something different, and having no idea which change did it. Then the next bag arrives and they are back to guessing.

Change one variable. Taste. Write it down if you are the sort of person who will actually do that. Two or three shots is usually enough to land a new coffee, and the note you make now saves you the same three shots next time.

Grind first, always. Temperature and dose are worth touching only once the grind is close, because until then they are rounding errors on a much bigger problem.

Espresso and filter pull different levers

The principle is identical but the practical controls are not.

On espresso, grind is doing almost all the work, because it controls how fast water forces its way through a compressed puck. Small grind changes produce large changes in the cup, which is why espresso feels fussy. It is not fussy so much as sensitive.

On filter, you have more room. Grind still matters, but so does how you pour, how many pours you do and how long the bed sits wet. Filter is more forgiving of a rough grind and less forgiving of a careless pour. If you are getting sour filter coffee, check that you are wetting all the grounds evenly before you blame the grinder.

The short version

Sour means stop-too-early: grind finer, go longer, go hotter. Bitter means went-too-far: grind coarser, go shorter, go cooler. Change one thing, change the grind first, and taste between each change.

Everything else is detail. If you want the rest of the detail, we wrote up the nine mistakes that wreck home coffee, and if your grinder is the thing holding you back, which grinder is actually worth buying. For keeping the machine honest, the espresso accessories you actually need.