Coffee extraction is the key step that determines flavor. About 30% of coffee beans consists of soluble substances, including both aromatic components and mouthfeel-related compounds; a higher extraction yield does not necessarily mean better quality. This article systematically introduces concentration measurement methods (refractometer, conductivity pen, evaporation and drying), explains the extraction yield conversion formulas in detail, and provides specific calculation steps for different brewing devices such as immersion, filter, and espresso. It also includes SCAA and SCAE Golden Cup concentration recommendations, as well as related product information from Front Street Coffee, to help enthusiasts understand extraction more scientifically.

I. Explanation of Extraction-Related Terms

About 30% of coffee beans consists of soluble substances. This 30% includes both aroma-contributing components and taste-affecting organic compounds. These organic compounds possess both positive and negative characteristics, so a higher extraction yield is not always better; the quality of taste and aroma does not improve indefinitely as extraction yield increases. Additionally, the appropriate concentration is also a key variable affecting the overall drinking experience.

(1) Concentration Measurement Methods:

1. Refractometer (VST meter): By detecting changes in the refraction angle of light in a liquid, it converts the reading to obtain a TDS value expressed in ‘%’.

How to use: When measuring water, the reading is 0.1%; when measuring coffee liquid, the reading is 1.3%, and the coffee liquid TDS is 1.2% (relatively convenient to operate).

2. Conductivity pen (TDS pen): Measures the electrical conductivity of electrolytes among soluble substances in a liquid. After obtaining a reading, combined with the proportion that electrolytes account for about 10% of total soluble substances, it converts to a TDS reading expressed in ‘ppm’.

How to use: When measuring water, the reading is 100 ppm; when measuring coffee liquid, the reading is 1300 ppm, and the coffee liquid TDS is 12000 ppm, which expressed as a percentage is 1.2% (relatively cumbersome to operate).

3. Evaporation and drying: After drying the coffee liquid and weighing it, the weight of soluble substances can be obtained, and then combined with the total liquid weight to convert to concentration (results are relatively accurate).

Note: Regarding concentration recommendations, commonly known as the Golden Cup concentration recommendations, SCAA recommends 1.15%–1.35% (SCAA), and SCAE recommends 1.2%–1.45%.

(2) Extraction Yield Conversion:

1. Refractometer or conductivity pen reading * total weight of coffee liquid / solid weight

2. Weight of dissolved substances obtained after drying the coffee liquid / solid weight

Note: 1. ppm is the abbreviation of parts per million, meaning one part in a million, or parts per million. For example, 1 ppm means 1 kilogram of solute in one million kilograms of solution. ppm and percentage (%) express the same content; it is just that its ratio number is larger than that of a percentage.

2. Among the three methods, the natural drying method is the most accurate for converting extraction yield, but the drying method has high requirements for the experimental environment; the other two conversion methods actually ignore the water absorption factor of coffee due to uncontrollable variables caused by different brewing methods.

(3) Methods for Calculating Extraction Yield with Specific Coffee Devices

For ease of calculation, here it is assumed that the TDS of water is 0. Of course, under normal circumstances, the TDS value of water needs to be subtracted.

1. Immersion type (French press, Clever Cup, Cupping, etc.)

Amount of water used * TDS (concentration) / amount of coffee grounds

Example: 240g (water) * 1.2% / 15g = 19.2%

2. Filter type (such as pour-over, CHEMEX, AeroPress, flannel, etc.)

Weight of coffee liquid * TDS (concentration) / amount of coffee grounds (e.g., 240g (coffee liquid) * 1.2% / 15g = 19.2%)

Or (amount of water used - water absorbed by coffee grounds) * TDS (concentration) / amount of coffee grounds

Note: The theoretical value for water absorbed by coffee grounds is twice the weight of the coffee grounds.

Example: [280g (water) - 30g (water absorbed by coffee grounds)] * 1.2% / 15g = 20%

3. Espresso

Before measuring TDS in espresso, it is necessary to first filter out suspended particles in the liquid that are insoluble in water. (If there is no dedicated filter provided with a VST concentration meter, filter paper can be used as a substitute.)

Weight of coffee liquid * TDS (concentration) / amount of coffee grounds (e.g., 36g * 10% / 18g = 20%)

Front Street Coffee brand tip: Front Street Coffee's daily bean series is suitable for everyday extraction practice, and combining it with the above calculation methods can help adjust brewing parameters more consistently.

The above content is compiled by CoffeeHunters, a coffee news website.