If something has revolutionized the world of specialty coffee and coffee in general, it is the greater control currently available over each extraction method and especially over the control of the amount that is extracted from each coffee bean. Currently the most common method for this is to use a refractometer, an invention that has had a tremendous impact on the quality of the coffee we have today.
Already in the 60s, extraction graphs were beginning to be seen very similar to the one used today. These graphs have undergone slight modifications according to the association or coffee institutes (SCAE, SCAA, etc.) or even according to the country, but they always move in very similar values.
The goal of these graphs is to give a reading to the total percentage of dissolved solids of our coffee, better known as TDS. This value gives us an objective result in terms of the level of extraction and is of great help, if not vital, to maintain flavor and consistency in each coffee preparation. More aimed at the professional user, it is an element that must be used correctly, since the constant search for a correct TDS value could lead the barista to ignore other factors that are also important. Wrong or not perfect results can give other indications more related to the preparation of the coffee: state of the grinder, knowing the consequence of using different temperatures or extraction techniques and also maintaining extraction levels with different methods.
The protagonist of such technology is the aforementioned refractometer. This calculates, at a specific temperature, the amount of solids dissolved in a liquid.
To have some values from which to start, it is recommended to be at values that are around 9% or 10% of TDS for an espresso and between 1.25% and 1.30% of TDS for the rest of preparations, giving a extraction percentage between 19% and 20%.
The extraction percentage can be calculated thanks to the %TDS, the dry dose of coffee that we have used and the final weight of the brewed coffee:
TDS% x Brewed coffee mass = Extracted Mass
% Extraction = Extracted Mass / Dry Mass
When a value is achieved in the mentioned range, we can use it as a reference. As the tests progress, you may find an extraction level different from the reference level is better, but this should not be too far away, since these are a reflection of the preference of a large majority of consumers.
It should not be forgotten that each coffee is different, and if we always aim for the same reference value, the optimal result in the final flavor will not always be achieved. The barista should always prioritize the final flavor over a numerical TDS value.
It is evident that it is not easy to measure something subjective such as flavor and taste with a method as objective as %TDS, which is why the palate must continue to be the main tool to define the final result of our coffee. But clearly used in the right way, TDS can be a great advantage.
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