If you've been following along in our detecting defects series, you may remember that we are moving forward in the coffee production chain to investigate defects occurring in Processing. Phase Two. (You may also be a little annoyed with me if you've been following along, since I've recommended that you taste some pretty awful cups.) Nonetheless, if you appreciate the end goal is to understand defects better and are still reading along, as a reminder, "Processing, Phase Two" (admittedly arbitrarily defined) includes the following activities which generally occur at a dry mill
- Drying of pulped (possibly fermented) coffee beans still in parchment or drying of coffee cherries with seeds still inside.
- Storage of coffee parchment
- Cleaning/sorting of coffee parchment prior to hulling
- Hulling (removal of parchment or removal of dried cherry husks depending upon method)
- Grading sorting
- Bagging for export
Looking at the long list above, you may think that I've made a mistake in including all of the above in one phase and, frankly, you're probably right. After undertaking my research and talking with millers in Colombia. El Salvador and Brazil. I've realized that I Should have broken processing into about 20 phases - or at least one or two more. Certainly, I could.
Many activities take place at the dry mill and these activities, if not carefully managed, can cause serious defects - even though of as Steven Diaz quality director for Expocafe. S.A. Colombia states, "The mill is designed for the sole purpose of removing physical defects by different means, "By means, Diaz is referring to various activities that take place in the dry mill, which, in theory, improve coffee quality by eliminating defects.
Categories of Dry Mill Defects
Indeed, Diaz is correct in stating that the milling process is, at least in part, designed for the purpose of removing detects that have occurred prior to reaching the dry mill. For example, equipment such as density, size and color sorters, and hand sorting are utilized specifically to remove defects. Nonetheless, activities in a dry mill also include drying of parchment coffee or cherries (the latter in natural processing) and dc-hulling coffee seeds from within parchment or from within the dried cherry husks. It is during these drying and hulling activities in particular that a dry mill may induce, rather than reduce, defects.
Defects Created at the Dry Mill
According to Jeff Holman, president, E1 Volcan S.A. de C.V., San Salvador, E1 Salvador, "Among the defects caused during the milling process arc the following : stained beans, smashed beans, black and semi-black beans". To this list, we can add sour, stinker, overfermented, and fungusdamaged beans, dried cherries / pods, and parchment, (See why I wanted to turn this into a 20- part series)
Causes / Identification
With such a long list of potential defects within a long list of activities at the dry mill, it's not very practical to focus on a specific defect. Instead, it makes sense to review a number of defects that have a lot in common despite having distinctly different visual and taste identification points. As we'll see, even though a variety of defects can occur in poor dry milling conditions, many of them share root causes.
In fact in general, according to Luis Pascoal, director of Daterra Coffee, Brazil, all defects that occur at the dry mill can be attributed to "lack of education / proper training a mindset for productivity and not for quality, lack of infrastructure, and, in times of high production, too much coffee". Ultimately, it seems true that these general
| DRY N ILL DEFECT CHART |
| Defect Name |
Causes |
Visual Identification |
Taste Identification |
SCAA Classification |
| Smashed, broken, Chipped. Cut beans |
Poorly calibrated hulling machine ; excessive friction |
Green and roasted beans That are broken, chipped and / or cut. Green beat, may have dark red or blackish marks |
Potential of Dirty, fermented and other off flavors created by the oxidation of broken beans and the resulting bacterial activity |
5 broken beans = I full defect |
| Stained / discolored beans |
Over drying moisture below 9% |
Off-color, dull, yellowish |
Diminished attributes ; greenish flavor ; possible grassy and goody flavors |
Unknown |
| Black / Partial black |
Inconsistencies or delays in drying that result in over fermentation |
Full or partial black opaque coloring |
Fermented / rotten fruit, dirt, mold, sour flavors |
Full black=primary defect; I full black = I full defect Partial black = secondary defect;
3 black beans = I full defect |
| Sour |
Inconsistencies or delays in
drying |
Light brown,
brownish or grayish
coloring and dull
appearance |
Fermented / rotted fruit foul, rotten fish flavor |
Unknown |
| Stinker |
Inconsistencies or delays in
drying |
Full or partial yellow or yellow-brown to red-brown |
Sour and vinegar flavors |
Full sour = primary defect;
1 full s= I full defect Partial Son, = secondary defect sour beaus - I full defect |
| Fungus damaged |
Cut and chipped beans during
pulping that allow fungus
growth, inconsistencies or delays
n drying; improper storage of
parchment in high temperatures/
humidity |
Yellow, reddish
brown spots / spores |
Ferment, mold, earth, dirt,
and phenolie flavors |
I fungus damaged beans=
I full defect |
| Cherry pods |
CAt the dry mill, dried
cherries / pods (natural
coffees) show up in green
coffee when hulling machines
are not properly calibrated
and maintained |
Dried cherry pods |
potential for ferment, mold, loss of acidity and aroma |
I cherry or Pod +
I Full defect |
| Parchment |
Poorly calibrated hulling
machine ; lack of density sorting |
Coffee in parchment |
Diminished positive attributes and potential woody characteristics |
5 parchment bean I full defect |
Notes
- Some defects in the chart above can also be developed on farm o in the wet mill, but we are including only causes associated with problems at the dry mill here.
Although discussed in processing phase one as potential defects from ovcrfermontation, sour, black and stinker beans are included a-in here with causes associated with mistakes at the dry mill.
|
conditions are the root cause of all defects occurring in the dry mill, which, on the plus side, makes prevention methods more focused. Nonetheless, in spite of common general causes for dry mill induced defects, we can still separate out a number of distinct defects, isolate their particular causes, and give you some tips on how to identify them visually and in the cup. Please see the defect chart on page 14.
Before moving on to look at some prevention methods, I think it is worth noting that a surprising number of defects are caused by inconsistent and improper drying. Many of us probably understand that the moisture content of the exported green bean is critical, but have we realized how important the process of drying coffee is to the ultimate quality of green coffee ? As Jorge Pacas, agronomist in E1 Borbollon, El Salvador reveals, "the worst problem we have ever had was fermentation or overheating of the bean in the patios or mechanical dryers." Pacas works with his uncle Eduardo Alvarez at a quality driven mill in El Salvador known for processing award-winning coffees. Even with their experience and understanding of the critical nature of drying, they can experience challenges. For example, when coffee is not moved correctly on the patio or in when in excessive heat builds up either on the patio or in mechanical dryers, then inconsistencies in drying yield defects like blacks, sours, stinkers and others.
Pacas emphasizes, "The most common problem is the stinkers, where wet coffees are trapped in the machine layers." Stinkers, as we see in the chart on page 14 and, perhaps remember from our previous discussion on overfermentation defects, have severe ramifications in the cup. Clearly, it is not enough for a mill to simply deliver a green coffee with the proper final end moisture content; a dry mill must pay close attention to how parchment reaches the appropriate moisture level.
Prevention
The good news for defects caused at the dry mill is that, unlike other categories of defects we've discussed in this series, these are almost always preventable. Pascoal broadly identifies prevention methods, such as training, discipline and infrastructure. By examining each one of these a bit further, we uncover some specific prevention methodologies.
Training
The benefits of proper training at the dry mill are fairly obvious. We all know that in every area of specialty coffee production - from growing all the way to the final shot pulled by a barista at a retail storeproper training is the key to quality. When talking about training at the mill level, Pascoal and others are referring to the knowledge of mill managers and employees in drying coffee on patios (and / or in dryers) and in calibrating, monitoring and maintaining equipment. When coffee is carefully dried and hulling and sorting equipment is properly maintained by knowledgeable operators, the dry mill doesn't create new defects and, better yet, defects caused by activities or circumstances on the farm and in the wet mill process are removed.
Discipline
Discipline comes into play by paying careful attention during the drying and milling process. As Diaz report, "usually mill operators take periodic samples in order to make adjustments on the go before it is too late." More than just knowing how to implement proper drying procedures and how to calibrate and maintain equipment, mill managers must take responsibility for monitoring the process and making adjustments regularly. "If they do not perform this activity," states Diaz, "they will end up with a finished lot which will probably be rejected by the QC person who buys the coffee."
Infrastructures
At the mill, infrastructure refers to the patios used for drying, mechanical dryers (if used), equipment used for hulling, grading and sorting, and the overall facilities. When the infrastructure is clean, calibrated, and well maintained, a dry mill serves its purpose to remove pre-existing defects while avoiding the creation of any new ones. To give a couple of specific examples around drying patios (since as we discussed improper drying is significant issue), Pascal mentions need for, "very good concrete patio / terrace with water drains for mold control and proper equipment to turn-over the cherries without walking over them because it breaks the outer skin and increases the risk of mold or fermentation." In addition, the size of the patio is important as producers with patios that are " too small tend to increase the layers and damage the coffee cherries."
Fixes
Ironically, many defects occurring at the dry mill can be fixed or, perhaps, more accurately stated, removed by other activities at the dry mill. For example, equipment utilized in the final stages of dry mill processing-the size sorters - density sorters, color sorters arc precisely designed to remove many of the defects mentioned above, assuming, of course, the machines are calibrated correctly. In addition, hand sorting, which occurs in most mills producing specialty coffee, serves to remove defects that have passed through earlier sorting stages.
Parting Comments
In the first couple of articles in this series, we honed in on one or at least a fewer number of total defects, which have had some very specific manifestations in the cup. Nicely, this has let! me with an easy job of recommending some, uh, interesting cupping assignments. This time, however, a longer list of defects prevents me from pushing a specific tasting task. Instead, I recommend that roasters revisit the role of green coffee grading and sorting as an important aspect of green coffee buying. This is not to say that defects caused in the milt don't have negative impact in cup quality (we can see in the chart that they certainly do), however, solid grading at the mill level and the demand of specialty coffee buyers in insisting that they receive properly graded coffees will likely prevent many of these defects from ever showing up in your roasting plant.
If you really want another cupping project, though, here you go : source out some fungus damaged beans and let me know how you find the flavors of ferment, mold, earth, dirt and phenol in the cup. If you're really lucky, maybe they will all show up at one time.
Andi C. Trindle began working as a barista in 1989, and, to her surprise, remains in the specialty coffee industry 18 years later. She currently works exactly where she belongs as a green coffee trader with VOLCAFE Specialty Coffee. Andi also consults lectures and volunteers extensively within the coffee industry both nationally and internationally. She is currently serving as President of the International Women's Coffee Alliance and as co-chair of the Cupping Subcommittee for the SCAA Training Committee.
Foot Notes
A dry mill (No. not that type of dry: you can still get a cerveza if you're touring a mill late enough in the day) is so named in contrast to a wet mill where washed processing activities take place. A dry mill incorporates the stages of coffee processing after pulping and washing in wet processing or incorporates the full processing of dry processed coffees. See the activities outlined above.
Really : not really
Too much coffee moving through a dry mill taxes the equipment, potentially causing equipment to shift out of calibration and potentially causing excessive heat and friction, which may damage beans. Further more, if a mill is overloaded, the chance for inconsistent or improper drying increases.
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Source: Roast, May-June, 2008
