My quick findings about sorting coffee


1. What are defective coffee beans?

2. Reason for defective coffee beans

3. Solutions for defective coffee beans

1. What are defective coffee beans?

The coffee beans that are blotchy, bleach, does not have color, broken beans, sour beans, etc are defect coffee beans and are not selected as a fine quality Coffee but; they can have a place in the market at a lower price. The reason that these beans are may not be fine quality beans are as follows:

  • Moisture and drying problem
  • Due to oxidization
  • Contact with soil, metal, dirty water and many more

The coffee beans that are not good quality effects the appearance and they show up in the roasting process as soft, pale and molted beans which will definitely affect your good coffee time.

According to the study of Fe N. Dimero, Marvin V. Vicedo, Christina B. Hernan and Jeanette A. Saenz, sorting of coffee beans:

  • Can significantly improve the green bean quality as well as the cup quality of the green coffee.
  • Complete removal of all types of defects increased the cup quality of coffee from “good” to “very good.”
    What can Coffee beans can be categorized as defected?

2. Reason for defective coffee beans

The following are the reason that Coffee beans are categorized as defected one:

  1. Dried coffee cheery
  2. Black beans, Sour beans
  3. Stinker beans
  4. Insect damaged beans
  5. Broken Beans
  6. Shells and stick and Stones

3. Solutions for defective coffee beans

These problems could be solved, the most effective way is to sort either by two ways: manual sorting or electronic sorting.

3.1. Manual sorting

The process of removing defected coffee beans by a person is manual sorting. In manual sorting, the person has to sit in one place sorting them one by one with their hand.

Photo by Max Panamá

3.2. Electronic sorting

The process of removing defected coffee beans by machine is electronic sorting. In electronic sorting, the machine does the all the hard work. These machines have the laser to detect.

Following table shows difference between Manual Sorting and Machine Sorting with respect to efficiency, reliability, cost and time:

Base Manual Sorting Machine Sorting
Efficiency Good or Fair Good
Reliability Good or Fair Good
Cost Cheaper Expensive
Time Time Consuming Less Time Consuming




Good research work. :slight_smile:

You might be interested: there are a couple of reflections on the social-economic model on the coffee sorter on the wiki. We introduced them after a discussion on the things you mention above, but also others, such as “sorting is in practice done by hand by people who are not even formally paid, like women of the house. A machine can free up their time, even if it does not directly save money”.


Thank you for that work Anu, and I think you gave a good overview of the various aspects of coffee sorting. For proceeding with the design of our open source optical coffee sorter, we are looking for additional details about the manual sorting process:

  1. How much can one worker sort per hour (under bad, average and good working conditions)?
  2. What is the typical error rate of humans when sorting coffee? (Look up “double picked” and “triple picked” coffee, which means the coffee goes through human sorting twice or thrice. There have to be statistics how much it improves through these added steps, and ways to calculate the error rate of the previous steps based on that. Can you try to make these calculations please.)
  3. What do workers in manual coffee sorting earn? 10-20 wage examples covering different countries and different employers (family farm, coop, large business) will give us a good impression already. Converting the wages in PPP (purchasing power parity) in addition to showing the in the local currencies will help us comparing them.
  4. How many hours can a person work per day for sorting coffee, and how does it affect the speed and error rate of the sorting if people work more or less than this?
  5. What are health issues experienced by people sorting coffee manually as their job? (I assume posture problems like neck tension, back pain etc.)
  6. What about work satisfaction? (Anecdotal evidence / stories are ok. We know that this is influenced by many factors which are hard to quantify for us via Internet, but you can also try to find a study about this very topic …)

When you find these, could you add them to your post above please? Much appreciated!


Thank- you @alberto. The content will be updated with more informations. It is very true that people can save their time if machine can sort the beans. I have not seen any coffee sorting machine in Nepal till now ( At least on few of coffee production houses where i had been :smiley: )

Sure matt , I am on it :slight_smile:

How much does an optical coffee sorter cost if you were to buy one? I looked on a search and saw many models (all optical) but could not find prices.

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The cheapest ones are ca. 12,000 USD on Alibaba for Chinese models. Or 50,000 USD for a small machine from U.S. based market leader Satake in used condition (!).

And thus the incentive to make an open source version.

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I had a talk with a commercial for a small sorter from an Italian company.

The sorter was interesting, because it was a laboratory model, so much smaller than the ones usually found on Internet. Even like this, the weight was more than 100 kg. The sorter was able to sort something like one ton of beans a day. The technology was based on a black and white camera. The guy told me that when ejecting one bean, the sorter would probably eject more than one bean, due to the speed and flow of the beans.

All these characteristics where far away of the needs of a small farmer with a few hundreds of kilograms of production a year. And also, the price was 35,000 €, which, even for a group of farmer is out of reach …


###Small Update :

  1. Worker Under:
  • bad condition: 4 kg/hour,
  • average condition: 5 kg/hour,
  • good conditions: 6 kg/hour
  1. Typical Error rate: 1%-2% which is accepted as per Specialty Coffee Association of America
  2. Worker earns $20-$30 per day
  3. Workers works 8 hrs per day
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Huh that’s all much faster than my own 1-2 kg/hour :smile: Interesting! Could you add the links where you found this information? A kind of “literature list” at the end will do, no need to link every bit of information separately.

Also I assume that the “error rate” means that the sorted coffee still contains 1-2% of bad beans (1-2 bad beans per each 100 beans). That’s quite a low error margin. It means that our machine has to have 98-99% accuracy. (Right now it has 84% accuracy, but that will improve with better and esp. more pictures of beans to train it.)