WHAT TO AIM
For clean and sweet coffee with a certain strength, all you have to aim first is evenness.
We believe "The evener you extract, the higher the TDS"; therefore, we recommend you to try getting higher extraction as possible on a fixed ratio to find your starting point.
Avoid creating channels
Though it’s hard to define “entire over extraction” in the coffee brewing, there should be local over/under extraction that caused by channeling. To minimize local over/under extraction, we recommend you to agitate the slurry properly to give appropriate turbulence that is intense enough to reduce the amount of channels and not too aggressive to cause choking.
Avoid creating bypass
It's almost impossible to completely avoid bypass when you brew with "regular" pour over coffee brewers except for Tricolate or Aeropress. To minimize bypass, your pour height/rate should be high enough to disturb the ground bed deeply. We also recommend you to pulse pour to keep the water level not too high to avoid excessive amount of bypass.
Consistent drainage flow rate
When the drainage flow is too fast in the former half of the brew, you are more likely to create channels or there are significant amount of bypass. On the other hand, slow drainage flow in the latter half indicates that there is clogging/choking in your brew. As a result, the drainage flow rate gets closer when you poured well, hence you don't worry too much about total brew time. Please don't misunderstand that consistent flow rate always guarantees the quality of your brewing. The most important thing is what cause the flow rate.
The higher the pour height, the more turbulence in the slurry.
When choking occurs, there is excessive turbulence or significant amount of fines migration; your pour height is too high or your grind setting is too fine.
We usually recommend:
Higher pour height for soft beans or larger dose(deep bed depth)
Lower pour height for hard beans or smaller dose
*how to tell the bean hardness: high grown beans tend to be harder and low grown beans tend to be softer.
The optimal pour rate depends on your pour height. Select your pour height, then adjust your pour rate just high enough to avoid letting droplets appear in the stream.
*Inappropriate stream with droplets: you can’t get the ground bed disturbed with this stream.
*Ideal vertical pouring without droplets in the stream.
Keep your pour height and pour rate stable
For even extraction, keep your pour height and pour rate as stable as possible.
Keep your stream vertical as possible
To maintain a vertical stream, move your kettle relatively slowly in a circular motion to leave your stream undisturbed.
Spin the slurry after each pulse
Do “the Rao spin” after each pulse to avoid channeling and uneven extraction. The spin break up the channels, in particular, laminar flow. Flat coffee ground bed after your brew is a good sign of even extraction.
*Flat coffee ground bed after drawdown.
Do NOT let the coffee bed appear(main pour)
When you pulse, resume pouring before the bed appears for consistent slurry temperature and better turbulence.
*The water level to resume pouring.
When the water level is too high, you are more likely to create bypass. Stop pouring before you fill up the brewer.
*Water level right after stop pouring.
The number of times your pulse affects water level directly. Pulse pour to avoid creating excessive bypass.
Rinse your filter with appropriate amount of boiling water
We recommend rinsing your filter and preheating your brewer beforehand with appropriate amount (200g-) of boiling water.
Grind fine enough that there are no boulders in your grounds
Boulders (especially coffee ground particles larger than 800microns) are one of the biggest causes of under extraction. Grind fine enough or sieve the grounds to make sure that there are no visible boulders in your grounds.
If you are using a refractometer, grind finer and finer until TDS and EY stop increasing on your recipe, then go back one notch. Basically, coarser grinding creates less amount of fines. Coarser grind setting is better unless it yields less TDS/EY.
*Flat ground bed without visible boulders.
Consider your beans hardness and size
Bean hardness affects your grinding and brewing quality especially when grinding with a hand grinder or home grade grinder. Hard beans can sometimes be ground as boulders, create more amount of fines or less efficiently extracted. Usually, smaller beans tend to be denser and harder than larger beans. If you are using a home grade grinder, we recommend picking some smaller beans before grinding.
Do NOT compress the dry grounds
If you compress the grounds, you’ll likely create clumps which can be a significant cause of under extraction and channeling. Do NOT level the grounds by your fingers or spoon, shake the brewer to make the bed flatten.
*exception: when you use cone brewer like V60, you can enhance extraction by digging the ground bed and creating a swirl in the middle of the ground bed with your finger or plastic/metal stick though it's not very repeatable.
RATIO and DOSE
We usually brew on a 1:17 ratio with a great commercial grinder and a Brewista Artisan kettle combination. We recommend a 1:16 ratio for some home grade grinders(except for high end hand grinders such as Comandante and Kinu).
To pre-wet the grounds evenly, we recommend a 1:3 ratio for pre-wetting.
Pour ratio for each pulse
We recommend a 1:3-1:7 ratio for each pulse to make sure that all the grounds are saturated and evenly agitated.
We recommend 18g for Hario V60/01, 22g for Hario V60/02, 20g for Kalita Wave 185 and 15-20g for Fellow StaggX. Dose up with the same brew ratio if there is channeling or choking in the brew, especially when it’s weak or lacking in flavors. Dosing also affects your pour height significantly. We recommend higher pour height for larger dose and vice versa to dig the ground bed appropriately, hence your total pouring time is usually almost same for every dose. Your main variables for different doses are not pour time but pour rate/height.
It is said that appropriate water hardness for coffee brewing is 60-130 ppm(it depends on your preference and balance of each mineral as well). If your tap water is out of the optimal range, we recommend Volvic for brewing water. Try softer water when your coffee is too heavy, lacking in flavors or bitter. On the other hand, brewing with harder water when your coffee is sour, lacking in sweetness, or weak.
Magnesium and Calcium
Roughly speaking, when the amount of the magnesium is not enough, your coffee will be hollow or lacks sweetness. On the other hand, the mouthfeel will be too hard/dry or not smooth when there is too much amount of calcium.
We recommend 96-98 celsius for your brew water temperature as a starting point(or just off the boil if you don't have electric kettle). Note that boiling water offer vapors that disturb the kettle stream.
The relationship between brew water temperature and extraction is quite simple. The hotter your brew water, the more you extract and vice versa.
Another factor is viscosity. Water become less viscous as it's getting closer to boiling (100Celsius).
OPTIMIZE YOUR BREW
Try variable brew water temperature
Since you have read our brew guides up to this point, now that you are very well at brewing coffee evenly. Lowering the brew water temperature is the only way we know to lower your extraction yield without interfering evenness of extraction.
We recommend you to try lowering brew water temperature until you hit the under extraction point that your coffee is sour, lacking sweetness or weak for you or the point that sweetness start decreasing.
We would say the best brew water temperature is the lowest one to hit your optimal tds/ey balance since water of low temperature is less likely to over extract each particle in the slurry(even a small particle).
When your coffee lacks sweetness or body or not viscous enough for you, your coffee is under extracted for your palate. When you over extract your coffee, it will be hard for you to detect flavors or sweetness due to excessive amount of plant fibers or dry distillation product. We usually aim for 1.25-1.30 TDS with 1:16-1:17 ratio.
* Note that plant fibers and dry distillation products are less likely extracted compared with other compounds. The "good compounds" almost stop diluting and dry distillation products start diluting at a certain EY if you extract the grounds evenly.
Kettle Stream Theory: Coffee Ad Astra
The Rao Spin: Mr. Scott Rao
See the collection below to try our brew methods!!