Coffee beans have a moisture content of roughly 60% when picked, and they should be dried to around 11–12% to avoid rotting while waiting to be sold and exported. A wet mill can range in size from a small collection of equipment on a single farm to a massive industrialized operation capable of processing massive quantities of coffee.
The wet mill is used to process coffee from the cherry stage to the parchment stage when the bean is dry but still has its parchment or pergamino layer on it. Most people believe that the outer layer protects the coffee and that it doesn’t start to degrade until the coffee is hulled to remove the parchment at the last possible moment before shipping.
Because some companies use very little, if any, water in their processing procedures, the phrase “wet-milling” is a little deceptive. It does, however, distinguish between this early step of processing and the later stage of hulling and grading, called ‘dry milling.’
There is little doubt that processing significantly impacts the cup quality of the coffee, and expert producers are increasingly manipulating the process to achieve specific quality. On a worldwide basis, however, these producers are pretty rare.
For most producers, the purpose of processing is to make the coffee as profitable as possible, and this is taken into consideration when deciding which processing method to utilize. Some techniques necessitate more time, money, or natural resources than others. Thus, it’s a crucial decision for any coffee grower.
Natural Processing: The Process Of Nature
This is the oldest way of coffee processing, sometimes known as the dry process. The coffee cherries are spread out in a thin layer to dry in the sun after harvest. Some growers place them on brick patios, while others utilize raised drying tables that allow for better airflow around the cherry, leading in more equal drying.
To avoid mold, fermentation, or rotting, the cherries must be turned regularly. After the coffee has dried completely, the outer husk of skin and dried fruit are mechanically removed, and the raw coffee is kept before being exported.
The natural process imparts distinct flavors to the coffee, which can be beneficial but sometimes unpleasant. However, if a producer does not have access to water, this may be the only option available to them, as it is in Ethiopia and parts of Brazil.
The dry method is generally only suited for low-quality or unripe coffee worldwide. The vast majority of coffee produced this way is processed as inexpensively as possible because it typically ends up in the domestic market and has very little value. A producer’s decision to invest in the drying tables required for the low return on investment appears contradictory.
However, some people prefer this method for producing high-quality coffee. They typically find it more expensive due to the additional labor involved in drying the cherries with care and attention. This method is still used in some regions, and there is a strong demand for the cup attributes that a well-processed lot may provide.
Regardless of the variety of geography, the procedure generally adds fruit flavors to the coffee. These are typically described as having notes of blueberry, strawberry, or tropical fruit, but they can also be described as barnyard, wild, fermented, or manure.
Those who work in the coffee industry are divided on high-quality natural. Many people think that coffees that taste incredibly fruity have a lot of value and are great for presenting the variety of flavors that coffee offers. Others dislike the wild flavors or are concerned about customers encouraging growers to use the natural process to process more of their coffee. With such an unpredictably variable process, a high-quality lot could be irrevocably destroyed, reducing the producer’s profits greatly.
Fully Washed: Processing That Has Been Washed
Before the coffee seed is dried, the washing process removes all of the sticky flesh. As a result, the chances of something going wrong while drying are substantially reduced, and the coffee is likely to be worth more. However, this method is significantly more expensive than the others.
A machine called a depulper is used to remove the outer skin and most of the fruit flesh from the coffee cherry after it has been picked. The coffee is then transferred to a clean tank or trough of water, where the remaining flesh is fermented away.
The pectin in the fruit flesh keeps it securely attached to the seed, but fermentation breaks down the remaining flesh sufficiently for it to be washed away. During the fermentation stage, different producers use varying amounts of water. This approach has some environmental issues, mainly due to the eventual fate of the wastewater, which can be hazardous.
The time fermentation takes is determined by several factors, including altitude and ambient temperature. The sooner this process occurs, the hotter it is. Negative flavors might develop if the coffee is left to ferment for too long. There are numerous approaches for determining whether a procedure is complete.
Some farmers rub the coffee until it squeaks, indicating that the fruit flesh has broken down and the seed is entirely smooth. Others place a stick in the tank and see if it stands up, supported by the slightly gelatinous water rich in pectin. If it does, the process is complete.
Following fermentation, the coffee is washed to remove any remaining particles before drying. This is typically done in the sun, with the coffee spread on brick patios or high-drying tables. The coffee must be turned repeatedly using large rakes, just as the natural process mentioned above, to guarantee slow and even drying.
When there isn’t enough sunlight or there’s too much humidity, some growers utilize mechanical dryers to dry the beans down to 11–12% moisture content. Mechanical drying is typically thought to be inferior to sun drying in terms of cup quality, and it appears that even drying on a patio in the sun may be too rapid to reach the greatest potential quality (see Drying Speed and Storage Potential).
While many high-quality coffee growers prefer the wet process to prevent flaws, it can hurt cup quality. Wet-processed coffees have a higher acidity, more complexity, and what is considered a cleaner cup compared to other methods. Cleanliness is used in the coffee industry to describe the lack of unpleasant flavors, such as off-flavors or extreme harshness and astringency.
Hybrid Processes (create)
The Pulped Natural Process
This procedure, primarily employed in Brazil, is the outcome of trials conducted by Pinhalense, a coffee-processing equipment manufacturer. The goal was to make high-quality coffees using less water than in the washing procedure.
The coffee is mechanically depulped after it is picked, removing the peel and most fruit flesh from the beans. It’s then taken outside to dry on patios or drying beds. There is a lower danger of flaws with less flesh surrounding the beans, but there is still enough sugar in the surrounding fruit to see a considerable increase in sweetness and body in the coffee. After de-pulping, this technique still necessitates careful drying.
The Honey (MIEL) Process
This method is similar to the pulped natural method but is employed in several Central American countries, notably Costa Rica and El Salvador. The coffee is de-pulped mechanically, although it consumes even less water than the pulped natural procedure. Depulping machines may usually be programmed to leave a certain percentage of the bean flesh intact.
The resulting coffee is then labeled with terms like “100% honey” or “20% honey,” for example. The word mail comes from the Spanish word mucilage, which means “honey.”
When more flesh is left on the beans, there is a greater danger of fermentation and flaw throughout the drying process.
The Wet-Hulled/Semi-Washed Process
Giling Basah is a term used in Indonesia to describe this technique.
After being picked, the coffee is de-pulped and dried for a short time. Instead of drying the coffee to 11–12% moisture content like the other processes, the semi-washed process only dries it to 30–35%.
It is next hulled, which removes the paper and reveals the green coffee beans underneath. The beans are then dried once more until they are dry enough to be stored without decaying. The beans take on a characteristic deep swamp-green color during the second drying process.
The semi-washed method is the only one that does not keep the parchment on the beans until just before delivery. Many consider it to be a sort of fault, but the market has come to connect the flavors with Indonesian coffees and hence does not demand that the practice be stopped.
Semi-washed coffees have less acidity and greater body than other coffees, and the procedure produces a variety of flavors, including wood, earthy, mustiness, spice, tobacco, and leather. Whether or whether this is desirable is a point of contention within the industry.
Many people believe that these flavors dominate the flavor of the coffee (much like the natural process does), and we rarely get to sample Indonesian coffees. Some Indonesian coffees, however, are produced using the wet method and worth seeking out. It should be stated clearly on the packaging, with the words ‘washed’ or ‘completely washed’.
Case processing times
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Hulling And Shipping(code)
The beans are still contained in their layer of parchment when they leave the wet mill (unless they were processed using the semi-washed method). The moisture content of the coffee is now low enough that it can be stored without spoiling. Traditionally, coffee is kept in repose (at rest) for thirty to sixty days.
Although anecdotal evidence shows that if this stage is skipped, the coffee will taste green and unpleasant until it has aged more, the traditional practice of holding the coffee in reposo has not been thoroughly examined. There’s also evidence that this stage affects how well the coffee ages once it’s transported, which is most likely due to the moisture content.
The coffee is sold after this period and then hulled to remove the parchment. The parchment has served as a protective barrier up to this point, but it also adds weight and bulk to the coffee, so it is removed to reduce shipping costs.
In a dry mill (as opposed to a wet mill, when the coffee was treated to remove the flesh and dry the beans), the hulling is done automatically. In addition to grading and sorting the coffee, dry mills frequently feature grading and sorting machinery.
The green coffee beans can next be hulled and fed through a machine that checks the color and eliminates any coffee with visible flaws. The coffee is next graded by hand after being sorted by bean size using huge shaking sieves with varied hole sizes.
This time-consuming technique is usually carried out by women rather than men around a huge table with a central conveyor or on large patios. They sort through their coffee and remove as many flaws as possible, sometimes within a set time limit by an automated conveyor.
This is a time-consuming process that adds significant cost to the coffee while also vastly improving its quality. It is definitely a difficult and monotonous job, and it is only fair that higher-quality coffees pay more so that those who perform this laborious task are well compensated.
Depending on the nation of origin, the coffee is now ready to be bagged in either 60kg (132lb) or 69kg (152lb) jute bags. In certain circumstances, the coffee is vacuum-packed and delivered in cardboard boxes, or the bags are lined with a protective material, such as a multilayer polyethylene, to make them moisture resistant.
Jute has long been the preferred material since it is inexpensive, easy to work with, and has a low environmental impact. New materials are being investigated as the specialty coffee market becomes increasingly worried about the condition of coffee during shipping and continuous storage.
Coffee is usually carried in shipping containers from the country of origin. Although low-quality coffees are sometimes just tipped into a huge liner covering the container’s walls, the waiting roaster will prepare the entire container on the day it arrives, these containers can carry up to 300 bags of coffee. The containers are dumped into a receiving station at the roasting factory-like dump trucks.
Transporting coffee aboard container ships has a low environmental impact (especially compared to other areas of the coffee industry) and is relatively inexpensive. The disadvantage is that the coffee may be exposed to heat and moisture, both of which can degrade its quality.
Shipping is also a difficult procedure, with bureaucracy in many countries causing roasters a great deal of stress as containers of coffee lie in hot, humid ports for weeks or even months awaiting paperwork. Many in the specialty coffee industry are dissatisfied with this part of the business because air freight is both environmentally unfriendly and financially unsustainable.
Sizing And Grading
Coffee has been classed by size in several nations for longer than rated by quality. Despite the fact that they are technically unrelated, the two are nevertheless regarded as connected. Different countries will have their own vocabulary for grading (see Common Size Grades).
Sieves, which are numbered to show the size of the holes, are commonly used for grading. Arabica was traditionally designated by even numbers (such as 14, 16, and 18), while odd ones designated Robusta.
After being hulled, the coffee is mechanically shaken through layers of sieves to separate the various grades.
Peaberry coffee (PB) is a classification based on the tiniest intact beans (not fragmented parts). When a coffee berry has only one seed instead of two, it’s called a peaberry. Although this may not be uniformly true, they are said to have a more intense flavor. Comparing the flavor of a coffee’s peaberry selection to that of the larger beans is always a fascinating experience.
While larger beans aren’t always better, having a small size range makes roasting the coffee easier, and the resulting roast is more consistent. This is due to the fact that different sizes of coffee beans have different densities. The smaller, less dense coffee beans will roast considerably faster than the larger, denser beans during roasting. This means that at least a fraction of a mixed batch of coffee will not have attained the appropriate roast level.