How do we know if the espresso extraction was good?

Using a refractometer to measure extraction yield in espresso can provide valuable insight into the quality and consistency of your espresso shots. Here's a step-by-step guide:

1. Calibrate the Refractometer: Ensure your refractometer is properly calibrated according to the manufacturer's instructions. For instance to calibrate the DiFluid R2 refractometer you have to take a sample of the water you are using for extracting espresso and pour on the lens and press the button 2 times shortly.
2. Prepare Espresso Shot: Pull an espresso shot using your preferred method and equipment. Keep all variables consistent for accurate measurements, such as grind size, dose, tamping pressure, and brew time.
3. Collect Espresso Sample: Use a syringe to collect a small sample of the espresso. The sample should be large enough to cover the lens (prism) of the refractometer. Then add the espresso filter on the syringe and push the espresso to go through the filter and drop on the refractometer.
4. Place Sample on Prism: Place a few drops of the espresso sample onto the prism. Be careful not to introduce air bubbles and make sure the temperature is not over 50 celsius degrees, as they can affect the reading.
5. Take Reading: Press the button to let the device start testing. The refractometer will provide a measurement of the Total Dissolved Solids (TDS) percentage.
6. Calculate Extraction Yield: If you got a smart refractometer like the DiFluid R2, you can easily pair the device to the software on your smart phone and see the result on the standard SCA chart or other standard charts. Also you can calculate the result manually. Once you have the TDS reading, you can use it to calculate the extraction yield using the formula:
   Extraction Yield (%) = (TDS %) x (Brewed Coffee Weight / Ground Coffee Weight) x 100
   • TDS %: Total Dissolved Solids percentage obtained from the refractometer.
   • Brewed Coffee Weight: The weight of the extracted espresso shot.
   • Ground Coffee Weight: The weight of the coffee grounds used to prepare the shot.
7. Interpret the Results: Typically, extraction yields in espresso range from 18% to 22%. Adjusting variables such as grind size, dose, and brew time can help you achieve your desired extraction yield.
8. Repeat for Consistency: For accurate results, repeat the process multiple times and take an average of the extraction yield measurements. This helps ensure consistency and reliability in your espresso brewing process.

By using a refractometer to measure extraction yield, you can optimize your espresso brewing technique to achieve better flavor and consistency in your shots.