A speciality coffee flavour note across London.
Potato defect presents as a distinctly savoury, raw-potato or earthy aroma and flavour in the cup, often described as reminiscent of uncooked starch or the skin of a waxy potato. It is considered an undesirable taint rather than a nuanced flavour note, and even a single affected bean can noticeably compromise an otherwise clean brew. The defect is caused by a bacterial infection, typically involving species of Erwinia or Pseudomonas, which produces isopropyl methoxypyrazine as a metabolic byproduct within the coffee cherry during or after harvest.
Potato defect is most typically associated with coffees from the African Great Lakes region, particularly those from Burundi, Rwanda, and the eastern Democratic Republic of Congo. It is thought to be linked to the antestia bug, an insect common to higher-altitude growing areas in this region, which creates wounds in the coffee cherry that allow bacterial entry. Washed coffees from these origins tend to surface the defect most clearly, though it can occasionally appear in natural-processed lots from the same areas.
Because potato defect is inconsistent by nature, it will not typically appear on a bag or menu as a listed flavour note, but coffees from Burundian or Rwandan origins may carry an honest producer note acknowledging its possibility. The defect tends to reveal itself most noticeably in filter and pour-over preparations, where the cleaner cup profile allows the savoury, starchy quality to come through without interference. If a cup from one of these origins carries an unexpectedly earthy or raw quality that does not align with the other listed flavour notes, potato defect is a reasonable explanation to consider.
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