Coffee Quality Control at Assembly Coffee

by Michael Cleland

A Guide To Quality Control In Speciality Coffee Roasting 

Quality control is a complex practice spanning all aspects of green coffee and roasting operations. This introduction will outline our specific objectives and procedures implemented for maintaining consistent production quality.

Consistent production quality is achieved via the interdependent relationship between:

  • Sensory analysis
  • Objective roasting data
  • Objective brewing analysis

Upcoming articles will expand on the specific interplay of these three aspects, explore the challenges of interpreting data and discuss the need for evolving parameters.

Quality Control requires constant testing parameters at the cupping table. We conduct QC analysis with:

  • Cupping ratio of 11g/ 230ml
  • Consistent grind size using EK43T
  • 93 degree water
  • Bespoke mineral dosing water supply with controlled hardness of 250ppm and pH tolerated between 6.8 and 7.2 (more on water to come in future articles)
  • Samples isolated for solubility testing at 15 minutes brew time
Charlie McKay


From a sensory perspective we are committed to consistency in achieving the most complex cup character, while working with a green bean’s inherent flavour capacity. 

Sensory analysis is conducted with standard cupping protocol. As filter and espresso roasts fulfil separate functions, the later is also evaluated in the context of an espresso brew. At this point any inconsistencies are immediately ‘flagged.’

As an example, any coffee which scores inconsistently or presents an uncharacteristic flavour profile will be isolated for cross referencing analysis.

Roast Data

After generating a roast curve which produces optimal sensory and brewing analysis data , the defined profile is then used as the measure for consistent production quality. 

Cropster software is then used to log all roast data to measure against. The real benefit of this, is to cross reference sensory and brewing data with reference to variables in the roasting process.

We monitor re-heat times and overheat protocols, independent of Cropster.

For example.inconsistent system temperature stability will both, be revealed by, and explain, fluctuations in sensory evaluation and solubility. 

Brewing Analysis

This stage of analysis is primarily concerned with maintaining consistency by evaluating the solubility of roasted coffee. It is also used as an indication of inherent solubility of a bean when developing optimum sensory and roast parameters. ‘Positive and negative solubility,’ and its effect on cupping analysis, warrants further exploration/ definition. This will be outlined in forthcoming articles.

Solubility is measured using a refractometer and used to calculate extraction which, although specific to the respective bean, will fit within the following parameters: in a cupping context.

  • Espresso - Extraction in cupping bowl which sits between 19% and 22%

  • Filter - Extraction in cupping bowl which sits between 21% and 24%

  • Blend - TDS% readings which do not exceed .05% between blend components

As an example, a blend roast pairing which does not meet the QC standards may be:

  • Component 1 - 1.03%

  • Component 2 - 0.99%

  • Component 3 - 0.89%

Maintaining consistent production quality, and quality control in a broader sense, is a perpetually evolving activity. It requires an open mind and commitment to improving means of generating, quantifying and interpreting data. There is no doubt that, as new approaches are created and resources become available, it will continue to progress.

Originally published: 19 Aug 2015