Defects in green coffee

Learn about:

  • fungal diseases of grains,
  • immature grains,
  • crystallising grains,
  • thevariety of faded grains,
  • sour,
  • insect damage to coffee cherries,
  • flattened,
  • black,
  • or bruised coffee beans.

Ideal green coffee beans before roasting are characterised by a uniform, olive green colour, but some abrasions, stains and other defects may be found.
Not only do they not look aesthetically acceptable, the taste may be even worse than it appears.

1. Fungal disease of the bean ('moldy coffee bean')

These arise from damp or poorly dried coffee beans. These are then very susceptible to mould formation or fermentation, which is seen as a defect. They are characterised by a musty smell or visible mould on the surface.

2. Immature coffee beans

These are still undeveloped before harvesting. They tend to be smaller in size and slightly lighter than fully ripe beans. They taste rather earthy and sour and so produce a weaker cup of coffee.

3. Faded coffee beans

- Old beans (old-looking) - have a lack of vibrancy in colour, indicating that they may be old or over-dried. These beans tend to lose their flavour and aroma over time, resulting in a flat and bland flavour characteristic.

- Shrunken coffee beans - smaller than normal beans, often due to excessive moisture loss during drying or processing. These beans are denser and may be unevenly roasted, resulting in inconsistent development and bland flavour.

- 'Quakers' (a well-known term in the coffee industry) - beans with a buttery appearance are fragile and often lack the required moisture content necessary for proper roasting. Such beans are harder to spot, but once roasted they are clearly visible - they will not turn the colour they are thought to be and will always be lighter than the surrounding beans. They will affect the flavour profile of the drink by their astringency and lack of sweetness.

- Streaked beans - have inconsistent colouring and spots on their surface, which may indicate inconsistent drying. This problem does not have a spectacular effect on the flavour, but it may affect the overall profile to some extent.

Also, find out how coffee beans are sorted at a selective roastery.

4. Insect damage to the beans

Pests feeding on coffee cherries create this type of defect. They create small holes or miniature tunnels on the surface of the bean. The defects are already noticeable when picked and taste earthy when roasted.

5. Full or partly black be ans

This is the most common defect in green coffee. It can occur when the bean is exposed to moisture for a long time. This defect leads to the formation of black spots or areas on the surface of the beans, indicating the growth of mould or microbial activity. The taste of these defects is characterised by a greyish brown colour after roasting, together with a bitter taste.

7. Sour beans

Such a serious defect in the bean may acquire a vinegary-sour taste as a result of improper drying, inadequate fermentation or bacterial contamination. Acidity can obscure the natural flavours of the coffee - rapidly reducing the correct taste of the resulting beverage.

Try coffee processed using the traditional washed method

8. Pressed/flattened beans

Can occur during transport or even storage. Such a problem leads to uneven density and damage to the bean structure. Flattened beans may roast unevenly and produce a bland flavour profile in the final cup.

9. Cut or nipped beans

They have visible scratches on their surface, often caused by careless handling during processing or transport. The scratches cause moisture retention. When roasted, the broken parts burn easily and quickly turn bitter.

Preventing defects in green grains certainly involves following good production practices, careful care of the soil and harvesting at the right time.
It is therefore important to find out about suppliers in advance.

Whether you're just popping in out of curiosity or roasting coffee at home for pleasure, be sure to keep an eye out for these defects.
Keep your storage systems clean and dry to maintain the quality of the beans. ☺

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