To an expert, green coffee is a text. It can be read bean by bean, telling the entire story of the coffee from the tree, through the processing, sorting and screening.
||One of the most complex botanical forms is a flowering tree or shrub , such as coffee. As the tree goes through its many cycles of growth and dormancy, flowering and fruiting, many critical needs must be met to ensure a plant that is happy, healthy and wants to make a lot of fruit. A coffee tree produces about one pound of roasted coffee per year! The seeds are an encapsulation of all the complexities of the trees, and with over 800 organic constituents that contribute to the cup quality of the beverage, it is 2.5 times more chemically complex than wine.
I am not an expert on defects (you have to work in the industrial/commercial end of the trade to see lots of bad coffee!), but I cup and roast coffee everyday. I prepared this image (below) from coffee samples in my "green coffee files" at the request of my customers. The image is not all-inclusive, and is not composed entirely of defects. There are charts of coffee defects available through the Specialty Coffee Association of America (scaa.org)
Do not misinterpret the presence of irregular beans in a coffee as the sole indication of its quality - what I call "eye-cupping". Dry-processed coffees will always have more irregularities. Uneven preparation can even be considered part of the character of the coffee - with the off beans providing maybe some of characteristic earthiness as with some Indonesians or dry processed coffees. The preparation is part of the "coffee culture" of a specific place, part of the common practice of the people who produce a specific cofffee. An inexperienced roasted can easily interpret the presence of more silverskin (chaff) that gives the coffee a very yellow appearance as a defect. You will see more silverskin on late harvested coffees no matter what the varietal.
Ultimately, the quality of a coffee is found in the cup.
- If a coffee has irregular beans it doesn't necessarily mean it is bad. The cup is ALWAYS the ultimate proving ground for the quality of a coffee. Some coffee by nature have a higher percentage of irregular beans and are considered top quality. It can be part of the character of the coffee - with the off beans providing a characteristic earthiness to the cup as in the case of many Indonesians or dry processed coffees. Even in coffees of top quality you can get a bad bean - as happened in a Cup of Excellence competition in Rwanda a few years ago, when a few top coffees had potato defect show up in the very late rounds.
- New crop wet-processed coffees are usually a deeper shade of green, but not necessarily.
- A black bean (which is also called a "stinker" in an old text I have) is a seed that fully rotted in the fruit
- A "sour" bean is also called an underdeveloped bean. These are detected visually by an off color and a very wrinkled surface
- Overripe beans are also called "floaters" because in wet-processing they float and are skimmed off the water's surface.
- Coffee is often sold at a particular screen size, such as 16 or 17/18. The presence of small and large beans compared to the norm is not a defect, but indicates some ineffectiveness in preparation.
- Peaberries are not defects and are often considered higher quality, for no great intrinsic reason. They will roast differently because of their size. They occur when one of the two ovules (or seeds/beans) aborts and the other can develop unrestricted into a round shape, filling out the space provided in the fruit.
- Not pictured are beans afflicted by a boring insect and foreign matter that counts as defects such as sticks, stones, seeds in their parchment, pods, fingers ....
- The Green Coffee Association has a page of defects and grading.
Two Important Questions:
What does good "new crop/ current crop" green coffee look like?
Firstly, good green coffee from many origins has a different look based on preparation standards, processing (wet, dry, semi, pulped, etc). The SCAA distributes a poster of the green coffee grades, but it is based upon wet-processed coffee, and is quite useless for judging other processess and odd-looking cultivars.
What does old green coffee look like?
Past crop green coffee may look different, dried out perhaps, but it may not; you have to taste it to be sure. An older crop coffee will generally roast more quickly, which the moisture content of the beans has most likely changed due to prolonged storage. What happens most often is that the bright coffees will fade, and start to taste flat. The coffee may also absorb the flavor of what it is stored in - and become "baggy".
- Some of the worst defects are impossible to see, phenolic coffee in particular. Phenol defect is found in many origins, but is most identifiable in Colombia and Brazil (I have encountered it in Mexico, Honduras, and Nicaragua to a greater extent than in El Salvador and Guatemala ... not sure what implications can be drawn from that.) No conclusive research has proven the cause of phenol in the cup, but it is one of the most obvious defects to taste. It is a dirty, sulpherous flavor, very potent both in the aromatics and cup flavors. And you cannot see it: the green and roasted seed appear as a wholesome coffee bean.
- Some have posited that the cause is on the tree, in particular that it comes from trees with a consistently sunny side and a consistently shaded side. Others say it is from bad processing, that it is microbial. Others say it is the tree's defence from the Broca (the coffee berry boring insect). Based on my experience, I side with the microbial explanation. Phenol shares sensorial attributes with volatile sulpher compounds, such as hydrogen sulfide. Whether this occurs on the tree or in the processing is unclear. Phenol defect can be present in some of the best coffees, produced at the finest mills.
Also of interest: Single Bean Macro Photos of Green Coffee and Weird Stuff We Find in Coffee