All of this seemingly theoretical content about extraction percentage and brew strength becomes clear when applied to the brewing control chart, which one can easily find online. Although ascertaining extraction percentage seems simple enough in theory, the reality of coffee quickly reveals a challenge. It’s impossible to weigh dry coffee in and then weigh it out after the brewing process to find out extraction percentage because the grounds have also gained water weight. The brewing control chart allows us to avoid this challenge and determine with relative accuracy what our extraction percentage is if we know two things: brewing ratio and the TDS of our beverage.
The brewing control chart is not unlike a tic-tac-toe board, consisting of 9 sectors, with the center sector representing the goal of ideal brewing. The Y axis plots the TDS or strength level and the X axis represents the extraction percentage. Then there are a number of fixed diagonal lines bisecting the chart that represent various levels of heavier or lighter dosing weight. The form reveals the approximate extraction percentage when you find the diagonal line that best represents the CBR which formed the basis of your brew recipe, then follow it upward and to the right until it intersects with the TDS reading on the Y axis that you received when testing your beverage. Scanning from this intersection directly down to the X axis will reveal the extraction percentage.
If you are not in the ideal sector, first confirm that that is where you want to be, then make sure that the diagonal line that represents your dose actually passes through the ideal window at some point. If the point you have plotted on the graph is prior to the range where your diagonal passes through the ideal window, then keeping all other variables the same, try a finer grind with the next attempt. If the point you have plotted is past the ideal window, coarsen your grind. Other variables, such as agitation, small changes to water temperature, and adjustments to the brew time can also be used to fine tune your recipe.
Competence in the use of the brewing control chart helps immensely. It can show you how consistent you are on your chosen brewing apparatus, and can help you achieve repeatable results, batch after batch. If you understand the chart and the variables involved in brewing, you can learn to hit your target time and time again, even if you choose a target that doesn’t fall within the SCAA’s ideal window.