In coffee teaching, the operation demonstration of the grinding machine should take into account the explanation of principles, practical operation demonstration, error correction and interaction with trainees to ensure that trainees master the core skills of different grinding equipment. The following is an expansion from five dimensions: equipment classification, operation process, key parameters, common problems and teaching skills, combined with cases and data to enhance teaching effectiveness.
First, classification of grinding machines and key teaching points
According to the driving mode and grinding principle, grinding machines can be classified into the following three types. When teaching, the characteristics of each type should be highlighted:
Manual grinding machine (suitable for teaching basic theories)
Core components: Ceramic/stainless steel cutter head, adjustable bearings, folding handle.
Teaching Focus:
Grinding uniformity: Demonstrate the influence of “unidirectional uniform rotation” on the fine powder rate (e.g., the fine powder rate of HARIO MSS-1B is <10%).
Torque control: Simulate the incorrect operation of “excessive force causing bean jamming” and explain the reverse jamming techniques.
Applicable scenario: Hand-brewed coffee teaching, emphasizing the relationship between “grinding degree and flavor” (such as coarse powder → prominent acidity, fine powder → enhanced bitterness).
2. Entry-level Electric Grinding machine (Suitable for home and small-scale teaching)
Core components: 40mm conical cutter head, 40-speed adjustment knob, 227g bean hopper.
Teaching Focus:
Scale calibration: Demonstrate the difference in grinding degree between “Italian Concentration #5” and “Hand Rinse #10” (particle size can be compared through a powder sieving instrument).
Residual powder cleaning: Simulate the error of “flavor cross-contamination caused by failure to clean residual powder” and demonstrate the brush cleaning process.
Applicable scenario: Comparative teaching of espresso and hand-brewed coffee, emphasizing the “correlation between grinding degree and extraction efficiency”.
3. High-end Electric grinding machine (Suitable for professional teaching and commercial scenarios)
Core components: 55-80mm cutter head, single-dose grinding chamber, Internet of Things monitoring system.
Teaching Focus:
Dynamic grinding compensation: Demonstrate the function of “automatically adjusting the grinding degree when the humidity changes” (such as Eureka Mignon Specialita).
Data monitoring: Real-time parameters such as “grinding speed, fine powder rate, and motor temperature” are displayed through the APP.
Applicable scenarios: SCA certification courses or commercial barista training, emphasizing “the impact of grinding consistency on product stability”.
Second, demonstration and standardization of operation procedures (SOP)
The following takes Baratza Encore as an example to demonstrate the standardized operation process:
Preparation before grinding
Step 1: Check the capacity of the bean bin (≤227g) to prevent motor overload due to overloading.
Step 2: Select the grinding degree based on the type of drink (e.g., hand brew →#10, Espresso →#5).
Step 3: Place the coffee receiving cup under the coffee outlet to ensure there is no residual coffee grounds.
2. Grinding operation
Step 1: Start the motor (press the power button), and slowly pour in the coffee beans (≤15g each time).
Step 2: Observe the grinding speed (15-18 seconds for hand-brewed coffee to produce 15g of grinding, and 8-10 seconds for espresso to produce 18g of grinding).
Step 3: After grinding is completed, turn off the motor and clean the gaps of the cutter head with a brush.
3. Inspection after grinding
Step 1: Use a 20-mesh sieve to sift the coffee grounds, ensuring that the fine powder rate is ≤12% (the standard for hand-brewed coffee).
Step 2: Weigh the powder output. The error should be controlled within ±0.5g.
Step 3: Record the grinding parameters (scale, time, fine powder rate) for reference in subsequent optimization.
Third, key parameters and teaching cases
The following parameters directly affect the quality of coffee and need to be strengthened through cases to enhance the trainees’ understanding:
Grinding degree and extraction efficiency
Case: The same coffee bean is ground respectively with #5 (extremely fine powder) and #10 (medium-fine powder) :
#5 Grinding degree: Extraction time 22 seconds, TDS 14%, prominent bitterness, rough texture.
#10 Grinding degree: Extraction time 28 seconds, TDS 12%, balanced sweet and sour taste, smooth texture.
Conclusion: The degree of grinding needs to be matched with the extraction method (Italian concentration → fine powder, hand rinse → medium-fine powder).
2. Grinding speed and heat control
Data: Professional models (such as Eureka Mignon) take 8 seconds to grind 18g of beans, and the motor temperature is ≤45℃. The entry-level models (such as Baratza Encore) take 15 seconds and the motor temperature is ≥55℃.
Impact: High temperatures cause the loss of coffee grounds’ flavor (such as a 15%-20% reduction in floral aroma). During teaching, it is necessary to emphasize “intermittent grinding” or “pre-cooling equipment”.
3. Residual powder rate and flavor consistency
Test: Grind continuously for 3 times and record the amount of residual powder:
Single-dose grinder (Niche Zero) : Residual powder rate <0.5g.
Traditional bean mill (Baratza Encore) : Residual powder rate 2-3g.
Application: During teaching, it is necessary to demonstrate the improvement of flavor consistency by “single-dose grinding” (such as reducing bitterness fluctuations by 20%).
Fourth, Common Problems and Teaching corrections
The following questions are frequent mistakes made by trainees and need to be strengthened in memory through comparative demonstrations:
1. The problem of stuck beans
Reasons: The beans are damp, the grinding is too fine, and the force applied is uneven.
Correction method:
Demonstrate the “Reverse handle to remove the card” technique (manual grinder).
Adjust the grinding degree to a coarser gear (for example, from #5 to #6).
Ensure that the moisture content of the coffee beans is ≤12% (which can be detected with a hygrometer).
2. The fine powder content is too high
Reasons: Worn cutter head, excessive grinding time, uneven crushing of beans.
Correction method:
Demonstrate the operation of “sieving fine powder” (separated by a 20-mesh sieve).
Replace the new cutter head (check it after grinding every 500 pounds of beans).
Avoid incorrect operations of “secondary grinding” (such as re-pouring coarse powder into the grinding machine).
3. Cross-contamination of flavors
Reason: The residual powder was not cleaned up and different types of beans were ground.
Correction method:
Demonstrate the “deep cleaning” process (using cleaning particles + brushes).
Emphasize the principle of “one bean, one grind” (for example, grind the light-roasted beans first, and then thoroughly clean the dark-roasted beans).
Fifth, teaching skills and interaction with students
The following methods can enhance teaching effectiveness and student participation:
Group practical operation and competition
Format: Divide the trainees into groups of three, and each group will use a different grinding machine (manual/entry-level electric/high-end electric).
Task: Complete the entire process of “grinding – sieving – brewing – tasting” within 15 minutes and submit the flavor report.
Reward: The best group will receive a coffee bean or grinder cleaning set.
2. Fault Simulation and Resolution
Scene: Manually set faults such as “stuck beans”, “excessively high fine powder rate”, and “flavor contamination”.
Trainees are required to diagnose the problem and propose a solution (such as adjusting the grinding degree or replacing the cutter head) within 5 minutes.
Evaluation: Score based on the correctness and efficiency of the solution.
3. Flavor comparison experiment
Experiment: The same coffee bean was ground with #5 (fine powder) and #10 (medium-fine powder) respectively, and then brewed for blind testing.
Objective: Trainees are required to describe flavor differences (such as acidity, bitterness, and smoothness), and summarize the impact of grinding degree on flavor.
Sixth, summary and recommendation of teaching tools
Core knowledge points:
The compatibility between grinding degree and extraction method.
The influence of grinding speed on flavor retention.
The association between residual powder rate and flavor consistency.
Recommended teaching tools:
Powder sieving instrument: Visually display the fine powder rate (such as 20-mesh screen).
Hygrometer/thermometer: Monitors environmental and motor temperatures.
Electronic scale: Accurately weigh the powder output and the amount of coffee beans used.
Guide to Avoiding Pitfalls:
Don’t easily believe the wrong notion that “the finer the grinding, the better”.
Avoid operations that cause the motor to overheat due to continuous grinding.
Do not confuse the cleaning process of “manual grinding machine” with that of “electric grinding machine”.
Through the above structured teaching, trainees can master the core operation skills of the grinder within 3 to 5 hours and understand the influence of grinding parameters on coffee quality.