Unpleasant coffee tastes and aromas
Coffee that smells…Very earthy
“Aromatic Taints” – earthiness is an aromatic taint inflicted on the coffee beans whilst in their raw state, when chemical changes take place. Most aromatic taints (such as straw and rubber aromas) can be OK in small doses, but are not welcomed when they become over-powering. The smell is usually transmitted when the coffee is drying on the ground, and particularly when drying in the cherry, or when being stored in the warehouse.
“Dry Natural” processing – the coffee cherry picks up more of the geosmine in the soil, so Dry Natural coffees (Arabica and Robusta) are more likely to seem earthy in flavour.
Coffee that tastes… Sour
Wet damaged beans - the green coffee was not dried quickly enough after processing, or became wet again somehow.
The fermentation process taken too far so that the beans become overly fermented, lending a sour taste to the beans.
Water damaged beans can taint an entire batch of coffee at origin – if the wet mill’s processing system, including washing channels or fermentation tanks, are not cleaned out properly between batches, then parchment coffee may be left behind and essentially be re-fermented. This extra time in the water will lead to sour beans which could taint the entire batch being processed next.
These problems will also account for medicinal or vinegary tasting coffees, which turn up more frequently than you may imagine.
The situation could be salvaged by extra sorting and removing sour beans after drying, or through rigorous cupping to identify fermented batches – either at origin (preferably) or once in the consumer country. However, quality processing and careful sorting and cupping at all stages would avoid these problems in the first place.
Coffee that tastes… Green or wild
Under-ripe cherries – like any fruit, any under-ripe coffee cherry is green and lacking sweetness and the coffee bean is also undeveloped in this way and can certainly be tasted in the final cup as stalkiness or astringency.
Poor selection of cherries – the cherries ripen on the tree at different times, so picking ripe cherries at the same time as under-ripe cherries (and not sorting them before processing) will affect the overall batch of coffee.
Green coffee too fresh – coffee that hasn’t been rested long enough in its parchment, prior to export and roasting, can have a very wild, green taste. This is even worse if the coffee is roasted more or less straight from the tree.
Cherries over-ripe and left on the tree too long – cherries that are allowed to ripen to full maturity – becoming a deep purple – or even dried on the tree also have a bizarre, wild flavour to them.
Coffee that tastes… Bitter, “off” or like a potato
High levels of quinic acid – quinic acid has a bitter taste, and the compound forms in higher concentrations the longer a coffee is roasted, and if coffee is over-brewed or allowed to stand in a jug on a hot plate for too long. So coffees that are too dark roasted, or over-brewed coffee, taste unpleasantly bitter.
Bad brewing or serving – see above.
Defective coffee beans – not every coffee bean that grows on the tree is going to be perfect. Insects, disease, damage in processing can all lead to defective coffee beans. This adversely affects the taste when roasted and it might only take a few in the roasted batch to spoil the whole batch.
Bad sorting: the dreaded “potato cup” (which really does taste heavily of potato) is a frustrating problem often found in Rwandan coffee, even amongst the very best and is a result of the bad, potato tasting beans not being sorted correctly after drying. Only careful processing, sorting and preparation of the green coffee (which costs more) can get the coffee to “Speciality Grade” status – where only a few, minor defects are permitted.
Coffee that seems… Aged or old
Poorly executed drying – green coffee that is roasted fresh but still tastes tired and old, is likely to have fewer positive aromas and taste rather flat and dull. If the coffee beans are over-dried (past their optimum moisture content level) then this can become a problem.
Drying too quickly – if the coffee dries too quickly or at too high a temperature it can damage the cell structure of the bean, and in essence begin the “roasting” process prematurely. The coffee will never reach its optimum aroma and flavour profile after this. This is a particular danger with artificial, drum driers which must be carefully monitored.
Storage problems – if the coffee is stored at too high a temperature, or for prolonged periods, then it will lose moisture more rapidly and taste aged.
The green coffee is old – after around 6 months from harvesting, the green coffee will gradually decline or at least have gone beyond its optimum quality. The loss of moisture and the danger of picking up aromatic taints (such as a taste of the sack it has been stored in) exacerbate the problem as time goes on. Faded coffee beans (yellowy rather than fresh green) also point to an age issue.
Coffee that smells and tastes… Musty, mouldy, wooden or like sacks
Aromatic taints – musty coffee has become damp, or been stored in a damp smelling environment. Mouldy tasting coffee should be avoided – it may well have got wet and gone mouldy, then roasted (which doesn’t kill the toxins). Wooden or sack-smelling coffees are likely to have been stored in a dry, dusty environment and green coffee can pick up the smell of its own sack.
Coffee that smells and tastes… Like chlorine
Phenolic beans - there’s very little a farmer can do to detect the beans that are phenolic and taste like chlorine, and no-one has firmly decided what actually causes it. One of the theories is that some coffee cherries go into a sort of protective shut down whilst on the tree, possibly ones heavily exposed to UV sunlight and that the chemical reaction in the bean causes this case. It most commonly occurs in Colombia but is known in other Latin American countries such as Nicaragua.
Finding a phenolic sample when cupping can be heart-breaking, particularly when the coffee is otherwise spectacular. A coffee entered into a competition (such as the Cup of Excellence) would be automatically disqualified if a phenolic cup was found during the judging process.
Coffee that smells and tastes… Stale
Oxidised – oxygen is coffee’s major enemy. Once a coffee has finished roasting, then it’s on a slippery downward slope towards going stale. Stale coffee has an acrid, off-sweet smell that only seems as bad as it is when put alongside freshly ground coffee.
Unless the freshly roasted coffee is going to be ground and brewed almost immediately, then it must be packed as soon as possible into airtight packaging. Ground coffee ages and oxidises faster than whole beans do.