Measuring Espresso: Using a Refractometer Properly
A reliable reading starts with the sample. Separate preparation, TDS measurement and extraction-yield calculation.
A refractometer can reveal differences that shot time alone cannot explain. Readings are comparable only when the sample and instrument are prepared carefully. The measured TDS value describes concentration, not quality by itself.
Before taking a reading
- Record the recipe: Weigh the dry coffee dose and the complete espresso yield. Note time, coffee and settings.
- Make the sample representative: Gently mix the espresso rather than examining a single layer.
- Allow it to cool: Let the sample reach room temperature before measuring. Also follow your instrument’s permitted measuring range.
- Prepare it as instructed: Espresso may require filtration to remove interfering insoluble material. Use the specified method rather than an arbitrary substitute.
- Check the instrument: A clean measuring surface, calibration according to instructions and sufficient battery power belong in the routine.
Measure and calculate consistently
Use the same preparation for comparative readings. If results vary widely, first check temperature, calibration, cleanliness and handling before changing the espresso recipe.
Extraction yield in % = beverage mass × TDS in % ÷ coffee dose. Enter TDS as a percentage number, for example 9.2 rather than the decimal fraction 0.092.
Our example: 21 g of coffee produces 42 g of espresso at 9.2% TDS. This gives 42 × 9.2 ÷ 21 = 18.4% extraction yield. The brew ratio is 1 : 2; EBF is 21 ÷ 42 × 100 = 50%. These figures describe different things.
What the reading cannot tell you
An average can conceal uneven extraction. The preferred concentration also depends on whether the espresso is served alone or with milk. Measure several repeats and taste them. Measurements should support sensory judgement rather than replace it.
A useful record
Record dose, beverage mass, time, sample temperature, preparation, TDS, calculated extraction yield and a brief flavour note. This helps distinguish changes in coffee or recipe from changes in the measuring procedure.
Technical editorial: Stefan Anzinger, SCA AST
Photo: victor muñoz · Unsplash License.
Image: weighing the dose; a scale does not replace a refractometer.
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