A new filter coffee grinder landed in our office today, getting a new grinder is always exciting but can also be quite frustrating as the amount of calibration required until you reach a grind particle size that gives you the coffee you desire can spiral out of control pretty swiftly. As we had to go about this process ourselves I figured why not write about what we're doing and why not give all you lovely people an insight and maybe some ideas on how you can go about doing so yourselves; because regardless of grinder and preferred brewing techniques the general steps are pretty much the same.
So let's begin with what we consider an ideal coffee to be, in our mind there are two check boxes that need to get ticked before any more tweaking is required. In no particular order:
1 - The coffee needs to taste yummy!
2 - The coffee needs to fall in the SCAE ideal zone, in the the SCAE (2007) Coffee Brewing control chart (below)
NOTE: If you're calibrating for Espresso there is a similar chart which has a different ideal zone that you need to aim for, this can also be found on the SCAE website.
X Axis = TDS and Y Axis = Extraction Yield
The two points most times pretty much overlap, as the chances of liking coffee that falls outside the ideal zone are pretty slim, but hey if you like strong bitter coffee (or weak watery coffee), this chart will also show you how to get there! It pretty much acts as a map, showing you where you are and once you get an idea of what variables you can adjust, it also leads you to where you would like to go.
This post though will only focus on adjusting one of the variables, namely the Grinder (as that's what we're calibrating), however have no fear we will have separate posts on each of the other variables.
I am going to use a V60 as my filter method to brew my coffee, I'll stick another more detailed post on how to brew a V60 at a later date (so once again, keep your eyes pealed ;)
Normal V60 expectations:
- Grind Size: Medium to course, smaller particles than sea salt
- Time: It should take between 2 - 3 minutes to extract the coffee
- Coffee: 15 grams to 250 grams of water (which means we will need to use the 60g line in the graph)
- Water: Filtered (straight out of the tap can have a large amount of dissolved solids that can affect the taste of the coffee)
So hear we go...
1) Use the middle setting on the grinder which should get you in theory between its finest and coarsest setting.
2) Get all the prep work done (heat water, jugs, measure out coffee and add to filter, etc)
3) Start timer and begin pour over, once the last drop has been extracted stop time.
4) If you got a time greater than 3 minutes it means that the grind size is too fine and needs to be made coarser, it the time was less than 2 minutes then the grind size was too coarse and needs to made finer. Once you have made the required adjustments start from step 2 again.
5) Once you get the time between 2-3 minutes you know that you should be close to the zone if not inside it already.
6) Time to get the refractometer out, these vary widely, they go from the optical hand held (for less than £20) to the electronic (for greater than £600) and once cooled pour some coffee onto the lens and get a reading.
Note: If you don't have a refractometer that calculated TDS or converts BRIX to TDS, a general rule of thumb is that TDS = BRIX x 0.85.
7) Calculate the extraction yield using the formula below:
Extraction Yield = (Brewed Coffee x TDS) / Ground Coffee Used
Therefore we know that:
- Brewed Coffee = 250g
- Ground Coffee Used = 15g
8) You should now know your TDS and Extraction Yield, the ideal zone (based on the graph at the top is):
- TDS: 1.2% - 1.45%
- Extraction Yield: 18% - 22%
For 15g of coffee you are looking at the perfect spot of TDS that is ~1.37% and extraction yield of ~20%, however anything close to this works and when at home anything within the general zone should make for great tasting coffee.
9) So what should you do if you are not in the zone? If your TDS/Extraction Yield is too high, it probably means that your grind size should be marginally coarser and vice versa if it it too low. However at this point it will just be tweaks as the fact that your are within the right time bounds means that these measures can't be too far off!
So there we have it, the grinder is now calibrated for use, but that said it is always good practice to ensure that the setting doesn't drift, which it will over time and will need re-calibration as a result.
We will have future posts that delve deeper into each of the parts above, but for now if you have any questions please send us a message or comment!
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