Coffee Analysis – Objective
Subjective analysis is a personal opinion derived from a personal experience. Subjective analysis is whether you like the cake or not whereas the objective analysis is the fact that it’s a cake. Objective analysis is definitive and fact based.
In a black cup of coffee there are 2 things we can measure definitively;
We will define strength as “how much coffee is in the cup” and we will define extraction as “how much coffee came out of the beans”.
A (black) cup of coffee is just water and coffee. But how much of it is water and how much is coffee? By using a device called a refractometer we can measure precisely the amount of coffee solids (dissolved coffee) and the amount of water. If the liquid has more coffee solids it will have a higher strength and it will have a lower strength if it has less coffee solids in it.
If the strength is different between two brews they are less likely to taste the same, so the strength helps us determine if our brews are consistent. But we can also use it to determine if we changed the brew effectively for any given situation (customer request).
Espresso coffee has a much higher concentration than filter coffee, so the strength is very different for each of those brewing methods. Espresso strength typically ranges from 6 to 12. Less than 6 would likely not be considered as espresso in the traditional sense, whereas more than 12 would likely be classified as a ristretto.
Higher strength means there is more coffee in the cup. But, the confusing thing is it doesn’t necessarily mean that much coffee dissolved from the beans. Extraction and strength are interrelated but can also be manipulated independently.
Coffee beans are about 30% water soluble. We say “about” because there is no conclusive evidence that there is an exact amount that cannot be dissolved (perhaps we haven’t discovered how yet?). So with water we can dissolve up to roughly 30% of the coffee beans, the remaining 70% does not dissolve.
But dissolving 30% of the coffee isn’t necessarily the goal. All roasted coffee has acidity and bitterness. The compounds that create those sensory experiences are not dissolved / extracted the same way. The acidic compounds dissolve easier, so the sourness of a coffee tends to be from lower extractions whereas the bitter compounds are a little harder to dissolve, they tend to come from higher extractions.
The same applies to the extraction for consistency, if the extraction is different between two brews they are less likely to taste the same. And we can also use the extraction % to determine if we changed the brew effectively for any given situation (customer request).
In the real business of coffee, when we brew a coffee we aim to get a suitable level of extraction and strength. Typically, the extraction range will be somewhere between 15-24%. If it’s less than 15% it will likely be too sour to drink whereas if it’s over 24% it will likely be too bitter to drink (without a sweetener).
This chart (or similar versions) are a great companion to your subjective analysis. They will give you a deeper understanding of how the brewing process effects what ends up in the cup. But. The chart will never be able to tell you if you made a good coffee. And the target range is only a guide, the ultimate goal is always someone enjoying the coffee so don’t feel bothered if you or one of your customers is very pleased with the taste and it’s not in the target range!