The calibration and precision adjustment of coffee grinders are key steps to ensure the quality of coffee extraction. It requires a comprehensive operation combining observation methods, data methods, tool assistance, and equipment characteristics. The following are the specific adjustment methods and analyses:
First, adjust the grinding degree by the observation method
Pressure gauge status: During extraction, the pressure rises slowly from 0 to 9-12 Pascals, indicating that the grinding degree is appropriate. If the pressure is too high (such as reaching 120,000 units) or the coffee liquid flows out in drops, it indicates that the grinding degree is too fine. If the pressure is insufficient or the coffee liquid pours down, the grinding degree is too coarse.
The ideal state of the coffee liquid is that it is long and slender, with the color gradually changing from dark to light, and the flow rate gradually increasing from slow to fast, eventually presenting a slightly light yellow color.
Second, adjust the grinding degree by the data method
Powder-to-liquid ratio and time: It is recommended to use the standard parameters of extracting 36 grams of coffee liquid from 18 grams of coffee grounds in 24 to 26 seconds. If the liquid weight has reached 36 grams within 20 seconds of extraction, it indicates that the flow rate is too fast and the grinding degree needs to be adjusted. If the extraction time exceeds 30 seconds and the liquid weight reaches 36 grams, it indicates that the flow rate is too slow and the degree of coarser grinding needs to be adjusted.
Adjustment of powder filling amount: First, adjust the powder filling amount. If the flow rate is still too fast, then adjust the grinding degree. If the flow rate is too slow, first reduce the amount of powder filled, then adjust the grinding degree to avoid filling errors caused by static electricity problems.
Third, tools assist in adjusting the grinding degree
Screen mesh test
Cupping standard: Use an 800-micron aperture sieve. After grinding 10 grams of coffee powder, the pass rate should be 70%-75%.
Hand-rinsing standard: The grinding degree is between the size of white granulated sugar, and the pass rate is approximately 65%-70%.
Standard for French press: The grinding degree can be slightly coarser, with a pass rate of approximately 60%.
Consistency of grinding degree: The distribution of grinding particle size can be visually judged through the screen test, ensuring the consistency of coffee grounds in different batches.
Fourth, adjust the grinding degree according to the characteristics of the beans
Influence of baking degree:
Light-roasted beans: The beans are hard in texture and have a low carbon dioxide content. The grinding degree needs to be adjusted to increase the extraction rate.
Deep-roasted beans: The beans are soft and prone to swelling, so the grinding degree needs to be adjusted to avoid excessive extraction.
Freshness influence: Fresh beans can be appropriately coarser in grinding, while old beans need to be finely ground to compensate for flavor loss.
Fifth, equipment characteristics and calibration
Grinding disc concentricity: Grind coffee powder with the finest scale. If fingerprints can be clearly left on the powder, it indicates that the grinding disc is well installed. If the fingerprints are blurred or cannot be left, the grinding disc needs to be recalibrated.
Rotational speed adjustment: Rotational speed affects particle size distribution. The faster the rotational speed, the smaller the particle size. However, it is necessary to adjust it in combination with the design of the grinding disc to avoid uneven particle size distribution due to inconsistent rotational speeds.
Engineering mode calibration: For some models (such as Doctor Coffee), the grinding volume calibration can be carried out through the engineering mode. It is necessary to record the weight of the slag box according to the operation steps and input it into the system to ensure consistent powder volume.