Tolerance bands and QC gates
How to set tolerance bands and quality control (QC) gates for brewing recipes, ensuring consistency while allowing practical flexibility in production environments.
- Coffee Basics Nerds
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Article 10 of 12 in Brew Recipes, Math & Scaling/
Tolerance Bands
- Define the acceptable range for key brewing variables.
- Prevents unnecessary micromanagement while ensuring quality.
- Typical bands:
- Dose: ±0.1 g espresso, ±0.3 g filter.
- Water Temp: ±1°C.
- Beverage Yield: ±2–3 g espresso, ±10 g batch brew.
- Brew Time: ±3–5 sec espresso, ±15–20 sec pour-over.
QC Gates
- Checkpoints where brews are measured, tasted, or logged.
- Act as safeguards against drift or equipment issues.
- Examples:
- Refractometer Readings: Confirm TDS/EY within Golden Cup.
- Sensory Cupping: Daily calibration with staff.
- Batch Logs: Record dose, water in, beverage yield, brew time.
Why They Matter
- Tolerance bands prevent over-correction from small, non-sensory deviations.
- QC gates catch systematic errors before they reach customers.
- Together, they ensure consistent coffee quality without paralyzing baristas.
Example: Espresso Recipe
- Target: 18 g dose → 36 g yield in 28 sec.
- Tolerances: 17.9–18.1 g dose, 34–38 g yield, 26–30 sec shot time.
- QC Gate: Pull 3 shots at start of shift, measure TDS/EY, taste and record.
Example: Batch Brew
- Target: 3 L batch at 1.35% TDS.
- Tolerances: 1.30–1.40% TDS, ±10 g beverage yield.
- QC Gate: First batch each day checked, subsequent batches logged for variance.
Summary
Tolerance bands provide acceptable ranges for recipe execution, while QC gates act as checkpoints to verify alignment with targets. Together, they create a structured but flexible system for consistent quality control in coffee brewing.