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Academic Talk: About Coffee Defects Why Coffee Beans Have Defects

Published: 2026-03-20 Author: World Gafei

Last Updated: 2026/03/20, Professional coffee knowledge exchange More coffee bean information Please pay attention to coffee workshop (Weixin Official Accounts cafe_style) In the 1990s, 20% of coffee produced in Brazil was considered to have Rio defects, that is, coffee had a strong odor, similar to drugs, phenols or iodine. In fact, this defect also occasionally exists in coffee produced in the country. At the time, there was a massive

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In the 1990s, 20 per cent of coffee made in Brazil was thought to have a "Rio" defect, meaning it had a strong odor, such as drugs, phenols or iodine. In fact, this flaw also occasionally exists in coffee produced in the country of origin. At that time, people carried out large-scale research and experiments in an attempt to find out the cause of this defect.

2-trichloroanisole (TCA) is considered to be the main cause of this defective smell. In all coffee with "Rio" defects, people found TCA in concentrations ranging from 1 to 100ppb. Less than 50% of the TCA originally found in raw beans disappears during baking. The precursor of TCA, TCP, is also present in most samples.

TCA is also the main culprit of wine cork contamination. Although the biochemical principle is still in the guessing stage, the most likely pathway for the formation of TCA is that TCP is affected by filamentous fungi to produce methoxy groups at a specific temperature and high humidity; another possible reaction is shikimic acid as a precursor, but this reaction has not been confirmed in the coffee field.

In a 1999 academic paper co-authored by Cantergiani and other authors, the author mentioned that TCA is also found in raw beans of Mexican coffee, giving coffee a "moldy or earthy smell". Smelly, methyl propofol and sec-butylmethoxypyrazine are also found in these contaminated raw beans. When a certain substance dominates, the defective taste of coffee changes from "Rio" to "moldy" or "earthy".

All the defects of raw beans are caused by the wrong production process, especially the storage of raw beans. Constant temperature and humidity control can effectively avoid the reproduction and breeding of microorganisms that cause "Rio" defects. If there were no fungi, TCP would not be converted into TCA.

TCP is a substance found in wood fungi. As for raw coffee beans, TCP may be present in wooden trays and may be absorbed by raw beans through gunny bags during transportation.

All in all, "Rio" is regarded as a defective taste by most European and American countries, but its unique flavor is loved by people in Greece, Turkey, Lebanon and some Eastern European countries. Perhaps some Brazilian coffee exporters deliberately give their coffee this taste to meet the needs of customers in some special countries!