How to read brewing control chart: locate the nearby of a good cup of coffee
Throughout history many people were lost on the ocean searching for all kinds of places, be it the Northwest Passage or El Dorado, the Golden City. The reason is quite straight forward: there is no frame of reference out on the open sea and if you take a look out of your window everything looks the same, an endless blue sea. The same thing happen when you brew coffee as a beginner, you know you have distance with a perfect cup, but you don’t know where it is and how to get. In order to successfully navigate the sea, we need two things: a map and instruments to determine our position.
The map: brewing control chart
Let’s talk about the map first: Not quite as enticing as the Golden City but much more real is the SCA golden cup. The golden cup is the Specialty Coffee Association of America’s (SCAA) gold standard for a cup of coffee. It is defined a Coffee-to-Water-Ratio of 55g/L and coffee preparation temperature of 93 °C. This is a tried, tested and much loved standard among coffee-experts around the world.
The map is called the brewing control chart. It was drawn by E. E. Lockhart about sixty years ago at MIT and is the result of years of hard work. Like every map, some knowledge is needed to read it properly.
The x-axis, i.e. the horizontal axis, denotes a quantity called extraction. It is measured in percent and describes the share of the grounds that has been dissolved in the water. The part that is left behind is the insoluble part and influences the body of your drink. For example: if you had ground 50 g of coffee and 10 g of it are dissolved, you reached an extraction of 20%.
The y-axis, i.e. the vertical axis, shows the strength of the coffee. It can be given as either percent or TDS. There is an easy conversion rule between the two: 1000 TDS is 1 percent. This number denotes the amount of total dissolved solids in the coffee. Coffee making is hence mainly determined by two different ratios - the ratio of soluble to ground (extraction) and the ratio of soluble to water (TDS). Given these two numbers, the extraction rate and the TDS, we can mark our position on the brewing control chart. This also tells us where we can find the golden cup on the brewing control chart: right in the middle, in the ideal zone.
For the golden cup we need an extraction of 18% to 22% and between 1150 TDS and 1350 TDS. Around the ideal zone we also find the reason for why a coffee might be too weak or too bitter. Bitterness is caused by too high extraction rates, weakness by a TDS that is too low. There are several ways of manipulating the final TDS of your beverage, for example the brewing time, the water temperature or the grind size.
The compass：TDS meter and scale
Now that we have spoken about the map towards the golden cup we are still missing an important part: our instruments for determining our position on the brewing control chart. In order to quickly determine the TDS of a cup of coffee you need a refractometer.
Previously, these devices were large and expensive. However, DiFluid has recently developed the DiFluid Refractometer, which is very affordable, small and easy in usage. With the DiFluid Refractometer you can determine the TDS of your beverage in four seconds. This already gives you the y-coordinate of your position on the brewing control chart. If you know the amount of water you have used and the total weight of coffee powder you have used, you can then also use the measurement of the DiFluid Refractometer to accurately determine your whereabouts on the brewing control chart. All you need is this simple formula:
TDS_Value*Water/Weight of Coffee Powder=Extraction.
Being able to precisely locate yourself on the map opens up a whole new world of options. In fact, recent findings point seem to hint that there might be two different zones of optimality hidden within this large zone of the golden cup. Armed with a DiFluid Refractometer you can start you own journey across the brewing control chart. DiFluid has also developed an app where you can record, compare and comment the different extractions and strengths you have experimented with and which you liked best.
With the DiFluid App you can plot out your own course and find out what makes the perfect cup of coffee for you.