19 Dec 2014

On Cupping Protocols and Coffee Extraction

In November I posted a photo on Instagram. In it were cupping bowls, a scale and coffee beans. It showed I weighed out 13 grams for my cupping. The first reply I got was why I dosed 13 grams, and why the dosage sometimes differed between companies.
At the time I was looking through our company's cupping protocol, checking and measuring each variable; roast degree and roast profile, grind size, ground coffee weight to water ratio, water temperature, extraction times. When cupping you want to make sure you taste the coffee at it's best. You do not want to approve or reject a coffee on the basis of a bad roast or incorrect extraction. 

When starting at a new company, you might want to run through the protocol. Every location has a different grinder, different water and thus may have a need for a slightly different cupping protocol. I read an old James Hoffmann's blog on cupping protocols and extraction, which was insightful but surprising all the same. Paraphrasing Hoffmann's conclusions were that:

  1. Most of the extraction happens in the beginning of the brew and then slows down, making the window of then to break the coffee very wide. (And maybe even irrelevant?)
  2. When breaking the coffee crust you basically stop the entire extraction process. (So let's stop having that discussion.)
  3. When breaking the coffee crust there is a bump in extraction, probably because of the agitation.
  4. When you use more water, the cup will cool down more slowly and will extract more from the ground coffee.

This last point is what caught my interest. not because of the conclusion and what that means, but because Hoffmann seemed so surprised by this. When reading the article all of a sudden he switches to all capitol letters to express his shock. But why is he so surprised at the time?

When one understands what extraction is, one cannot be surprised that more water equals more extraction. And so again the question arises, what is extraction?

What is extraction
Very plainly put, this is extraction of infused coffee* measured in percentages:

(% total dissolved solids) x (brewing water weight)
ground coffee weight

TDS gives you a percentage of strength of the coffee. Extraction is what flavours you yielded from the coffee grounds. For the total dissolved solids (TDS) you need a special measuring device. But other than that, you can calculate your extraction percentage. 

For example, you measure that your TDS is 1.2%. Your brewing water weight is 200ml (which is 200 grams). Your ground coffee weight is 12 grams.

You get:

1.2 x 200

Which is 20. So you have an extraction rate of 20%. 

Ideally you want your extraction rate to be between 18 and 22%. Under 18% you have not extracted all the flavours you might want in your cup, leaving it watery and often sour. Over 22% you have extracted too much flavour, leaving the coffee quite bitter with a dry aftertaste. 

So what happens when you throw up the brewing water weight? Exactly, the extraction rate goes up. It is how the formula, and thus coffee extraction, works.

It is for the same reason all baristas will say the coffee to water ratio is so important. You wouldn't dose the same when making a litre of coffee or just half a litre, would you?

What does this mean for cupping?
So why could you not just measure out your cupping protocol and never look back? Alas, extraction is still a bit more complicated than that. There are a few variables you could take over from the SCAA cupping protocol, like roast profile, water temperature and coffee to water ratio. However all equipment is not created equal. So 93C on one boiler can be 95C on an other. Also the SCAA writes:
Samples should be weighed out as WHOLE BEANS to the predetermined ratio (see above for ratio) for the appropriate cup fluid volume.
But grinders always 'swallow' a bit of the coffee you grind through it. Meaning, if you throw in 12 grams of beans, you get less than that in ground coffee. Each grinder 'swallows' differently in degree and consistency. So you might want to either know how much of ground coffee you lose on average, or work with weighing out ground coffee instead of whole beans. Do make sure that, when weighing out ground coffee, you do grind per cup. This way you keep potential defects limited to one cup only.

An other very important, for some the most important, variable is the composition of the water. According to the SCAA the water needs to be clean and odour free, not distilled or softened, with a TDS between 125-175 ppm. But still the extraction level could be different between locations with the same ppm measurements. This is due the fact that TDS is a sum of ions in the water. What kind of ions and how much of particular ions is not measured. But all ions, in relationship with other ions, can deliver a different extraction. 

And so you need to do your own measurements. Regularly, as your water and also grinder burrs change. And you need to use and trust your tongue to compensate for all those things you cannot (yet?) measure. And so the Dutch saying 'measuring is knowledge', becomes 'measuring is some knowledge'. 

Back to Hoffmann
Now although Hoffmann's conclusion did not shock me as much as it shocked him, it does raise a valid point. We need to be more careful about dosing our water. Should we just eye what we pour into our cup, or should we put our cupping bowl on a scale when adding water?

It would be better to put your bowl on a scale, however one also needs to be practical. And when cupping 20 coffees a day, with 3 to 5 cups per coffee, one simply really cannot put every single cup on a scale, unless surrounded by a massive team. But it is good to remember the importance of being precise and understanding why certain cups might taste a little irregular. It is not always the coffee, it could be you.


* = This formula is only for infusion methods. For percolation methods, including espresso the formula becomes:

(%TDS) x (brewed coffee weight)
ground coffee weight

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