In several stages of the post-harvest of coffee such as fermentation, washing, drying, storage, and roasting, irreversible changes occur that affect the quality of the product. For this reason, they are considered as critical points in the coffee process, in other words, if the coffee bean deteriorates in one of these stages, the defects caused cannot be reverted to good quality beans in the following stages. Through the application of good agricultural and manufacturing practices and systematic controls in the production stages, defects can be prevented and the consistency and quality of the coffee can be improved.
Coffee defects occur when the beans or the beverage lack the expected qualities of the product. In the language of food quality, the term "defect" refers to deviations and non-conforming products. Coffee defects damage the physical aspect of the beans, give bad and unpleasant aromas and flavors in the beverage or cause a loss of its innocuousness.
Coffee beans with defects such as broccolored, black, moldy, contaminated, vinegar, discolored, and bitten deteriorate the quality of the beverage because they produce strange, rough, acrid, dirty, contaminated, phenolic, chemical, earthy, moldy, sour, fermented, stinker, nauseous or rested flavors, and also risk the innocuousness of the coffee. Therefore, they should be avoided, controlled, and removed before processing and final preparation of the product.
A visual inspection of green coffee serves only as a reference for the buyer but does not form part of the specifications for determining the quality of a coffee. The color range of unroasted coffee goes from green-blue to a more brownish tone depending on the origin or age of the coffee.
Defective beans can originate from the crop, mainly due to pests such as the coffee berry borer. However, the majority of coffee defects result from inadequate processing.
Defective beans can originate from the crop, mainly due to pests such as the coffee berry borer. However, the majority of coffee defects result from inadequate processing.
1. Defects of the first group: full, partial, or dry black beans, whole or partial vinegars, yellow or carmelite resting, and amber or butter.
2. Defects of the second group: loose, bruised, discolored (streaked and bleached), bitten or cut, bitten by insects, over-dried or burned, split, misshaped or deformed, immature, flattened, floated or rafted, damaged or faded.
Frequencies of defects in coffee: In the results of investigations carried out with coffee from several farms and in quality analysis of coffee in the winery, the most frequently detected defects have been brocaded, fermented, rested, contaminated, and moldy (1, 2, 14, 15).
When two defects are found simultaneously in a coffee bean, the defect that has the greatest impact on cup quality will prevail over the others. Each type of defect is counted individually; the assessor will not combine counts of defects of different types to calculate a combined equivalent defect. Malformed or misshapen beans are not defects, only defects that fall into category 1 and category 2 are considered in this guide.
Black Kernel - Partially black.
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Physical description: Black kernels are distinguished by their opaque color.
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Effects that occur in the cup: fermented flavor, acetic cup acid, rancid/earthy, musty/wet, sour, or phenolic. In addition, another problem that is generated is the risk of ochratoxin.
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These are due to agricultural causes. Blackening is the result of over-fermented pigment associated with microorganisms.
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Corrections
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For the agricultural segment, black beans can be avoided by harvesting only ripe fruits from coffee trees, thus avoiding conditions for over-fermentation during processing at the plantation.
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For processing, black beans become evident when the parchment is removed. They are generally slightly smaller and less dense, and some of them can be removed by sieving and sorting according to density. The most effective way to remove them is manually (hand sorting) or mechanically, using a sorting machine.
Sour kernel - Partial sour
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Physical description: Sour kernels can be recognized by their yellowish or yellowish-brown to reddish-brown color. Normally, the embryo within the kernel is dark or black in appearance. If the bean is cut or scraped, it releases a sour vinegar-like odor. Once roasted and ground, a single sour bean can contaminate an entire pot of coffee.
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Effects that occur in the cup: sour, fermented, acetic acid, depending on the degree of fermentation of the bean. Other problems: Affects the appearance of the green bean.
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Agricultural and processing causes of sour beans are a consequence of fermentation, thanks to microbial contamination at multiple points during harvesting and processing. Some specific causes are: picking overripe cherries, picking fallen cherries, water contamination during processing, or over-fermentation in the fruit while still attached to the tree in wet conditions.
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Corrections for this case could be:
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For the agricultural part harvest exclusively ripe cherries (avoiding overripe cherries), do not pick fallen cherries, and do not grow coffee in low-altitude areas close to lakes, rivers, or dams to avoid fermented sour beans.
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Processors can avoid sour beans by a) Ensuring that the pulping process is carried out at the right time (pulping cherries immediately after picking, avoiding storage of cherries for long periods). b) In fully washed coffees, the fermentation time in the tanks should be controlled. c) The use of contaminated or recirculated water during the washing process should be avoided. d) It should be ensured that the drying process is carried out at the right time, avoiding interruptions. e) Sour beans are revealed when the parchment is removed, and color sorters or manual sorters can be used to eliminate most sour beans.
Fungal damage:
- Physical description: Fungus-damaged kernels, as they are commonly called, are recognized by their yellow to reddish-brown powder-like spots (spores) in the early stages of attack, and grow in size until they cover the entire kernel. Grains damaged by fungi release spores that contaminate other grains.
- Effects that occur in the cup: It can produce fermented, rancid/dusty, moldy/moist, and phenolic flavors in the cup and the risk of ochratoxin are also likely.
- Its causes are agricultural and processing. Fungal-damaged beans are generally caused by fungi of the genus Aspergillus, Penicillium, and Fusarium, which can infect beans at any time between harvesting and storage as long as temperature and humidity are at levels that favor the growth of these fungi. Fungal growth will only occur under these conditions if spores are present.
"Broca" or insect damage :
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Physical description: Kernels attacked by the borer, as they are often called, are distinguished by tiny dark perforations (between 0.01 and 0.06 inches - between 0.3 and 1.5 millimeters in diameter). The path can form any angle, including longitudinal. Some grains may suffer substantial damage, with 3 or more perforations being common. These severely insect-damaged kernels count as 5 affected kernels = 1 complete defect. Slightly damaged kernels with 4 or more perforations are also frequent. These severely insect-damaged kernels count as 10 affected kernels = 1 complete defect.
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Effects that occur in the cup: It impacts the appearance of roasted coffee beans, and can generate rancid/earthy, sour, or musty/wet flavors, especially if present in large quantities. Among its risks is ochratoxin, which affects the appearance of green and roasted beans.
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The origin of the problem is agricultural. CBB is one of the most important pests in coffee agriculture. The CBB (Hypothenemus hampei) burrows into the cherry while it is still on the tree, tunneling into the soft part of the seed to reproduce. Newborns usually emerge from the other side, creating a kernel with two holes in it. It is not uncommon to find a kernel with several different paths. The incidence of CBB tends to decrease with increasing altitude.
Among the corrections that exist are:
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Agricultural: The best way to avoid coffee damaged by CBB is, after detailed inspection, to eradicate the conditions that favor its spread. Chemical spraying is one option, but its limited effect has led to a focus on integrated pest management techniques (such as certain specially designed fungi: Beauveria bassiana) and the use of African wasps (C. stephanoderis); since these beetles reproduce inside the seed, it is necessary to collect all the cherries that fall to the ground to eliminate their proliferation conditions. In addition, the ripe cherry pulp can carry the insect, so they should be kept at a reasonable distance from the coffee trees until composting has been completed. It is unreasonable to expect pickers to distinguish between healthy cherries and cherries damaged by insects since the damage caused is usually visible on the inside without close examination.
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Processing: Once sent to dry milling, insect-damaged coffee will become apparent when the parchment is removed. At this stage, density graders can remove most of the brocaded coffee. In case of severe infestation, coffees should be hand sorted. A massive CBB infestation can be catastrophic for farmers, rendering much of the crop unfit for export.
