There are two parts to making great brewed coffee: getting the flavour right and getting the strength right. You need to start with flavour, and then move onto strength.
With regard to flavour: extraction is what we’re interested in controlling here. Only about 30% of the coffee bean is soluble in water – the rest is cellulose. Of that 30%, we want to extract about 20% – this is the best tasting stuff. When we’re talking about coffees, we often will say that it’s ‘over extracted’ or ‘under extracted’. Generally we’re talking about how close to that golden 20% we are or not.
When you nail it, your coffee should be balanced and super sweet, with complex, defined acidity and an incredible mouth-filling richness. The finish should linger in your mouth for a long time, but it should be a delicious clean and sweet character – Matt Perger describes it “as though someone has left dark brown sugar on your tongue, or as though you’ve just finished a toffee.”. Properly extracted coffee is sparkling. That’s what you want, and once you’ve had it you’ll never go back.
Coffee that is underextracted (below 20%) can be described as:
- no aftertaste
Coffee that is overextracted can be described as:
This all sounds very serious, but do bear in mind things are on a slider – it’s not binary. See the diagram:
There are lots of things that affect extraction when we’re talking about brewed coffee, but here are the primary ones:
Grind size (i.e. how big or small the pieces of coffee are)
This is our independent variable – the one that we adjust. Smaller coffee grinds have a greater surface area, allowing water to wash more of the solubles off. Bigger coffee pieces leads to the opposite. You can increase or decrease the extraction by changing the grind size.
A general rule of thumb: If it’s bitter, astringent or dry, grind a bit coarser. If it’s empty, thin and sour, grind finer.
Steep/brew time (i.e. how long the brew takes)
This varies according to the brewing device, but usually you are looking for a brew time between 3 – 6 minutes. Interestingly enough, the brewing time you want doesn’t really change very much as your batch size increases or decreases.
Agitation (i.e. how much you stir it during brewing.)
To achieve a good extraction, agitation is almost always necessary as it promotes even and thorough wetting of the coffee. In the brewing guides I have written, I have specified when and tried to give a feeling for how hard you should agitate. With some brewing methods, generally, this is a control variable too.
Water temperature (i.e. how hot the water is)
This affects both the extraction and the quality of the extraction. It’s hard to accurately control water temperature with most manual brewing methods, although some are better than others. When we make coffee, the water acts as a solvent to strip the bean of the solubles we like (good tasting things). The temperature affects how efficient of a solvent it is.
- More temperature = more extraction.
- Lower temperature = lower extraction.
Use water that is around 95 degrees C for most brewing devices. We actually want to brew at about 93 degrees C, but we lose a few degrees to the atmosphere. Boiling a kettle and leaving it to cool for a minute or so is usually good enough, or you can geek out with a temperature probe or a programmable kettle like the BonaVITA.
It’s key to preheat your brewing vessel too – otherwise, it may suck heat out of the brewing water, lowering your slurry temperature and therefore, your extraction. Professionals use a refractometer to dial in extraction %, but at home there is no need to go that far. We just want to make a great tasting cup.
Do this test over the course of some days or weeks:
Every time you make a brew, use the same coffee bean, method and ratio. With each brew, make the grind slightly finer. This will increase the extraction ever so slightly. Probably, the coffee will get better and better each brew. Taste it objectively and record the results. Be honest with yourself and make sure you make note of any different things that happened in the brew. I have made some brewing record sheets to help people with this. The idea is that we increase the extraction until the coffee becomes bitter (over extraction). Then, you turn back the grind size to the size bigger and there you are! The coffee should sparkle. If it doesn’t….why not? Perhaps your coffee just tastes bad…
Now you can adjust the strength.
This is personal preference. Personally, I prefer weaker filter coffee because I find I get more clarity in the cup and it’s easier to taste. If you were to put milk in coffee, though, you might like it slightly stronger to compensate for the dilution that occurs when milk is added. We adjust the strength by changing the brewing ratio. This is the ratio of coffee:water used in a brew. Espresso coffee usually uses a ratio between 1:1.5 and 1:3, which is why it’s so strong. Brewed coffee, on the other hand, uses a ratio between 1:15 and 1:20, which is why it’s much weaker. Once you have your grind size nailed, you can work on the ratio. At home, I have a ratio sheet stuck to the wall beside my coffee makers.