January 28, 2021

Exploring post-harvest practices & their relationship with coffee quality

The price of coffee is determined by the C market, which is based on supply and demand. For specialty coffee, however, a price premium is paid, which is determined by cup profile and overall quality. This is generally represented by a score on an 100-point scale, where specialty coffees score above 80.

To improve the quality of their coffee (and subsequently earn a higher price for their crop), producers may seek to change practices on their farm. Unfortunately, some do not know where to start. Quality is influenced by a nearly limitless number of factors throughout production, including genetics, climate, and soil health. 

However, one aspect of the production process that can be controlled is what is known as “post-harvest”. These comprise the practices that take place once the coffee has been picked. 

To learn more about post-harvest practices, we spoke to three coffee producers in Brazil, the largest coffee producing country in the world. They told us about some of the post-harvest practices they use to help them break the 80-point barrier and improve the price they are paid for their coffee.

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Post-harvest practices: A breakdown

Cedro Fornari is a specialty coffee producer at Sítio Refúgio do Cedro in Caparaó region of Espírito Santo, Brazil. One of his lots came third in the Brazilian Coffee of The Year competition in 2020. 

Cedro says: “Post-harvest practices are all the care and handling you have with your beans. It is a period that requires an extra focus to avoid mistakes and guarantee the quality of the [cup].”

Marcionilia “Nila” Venância Ramos has just started to produce specialty coffee. On her farm, Formigas do Café, she says she previously only grew commodity-grade coffee. However, in 2020, her first lot was graded specialty.

“Our post-harvest practices ensure that the beans are handled the right way at the right time,” Nila says. “This means managing local hygiene, drying time, temperature, and so on. [As a result], the beans don’t lose quality at any of the stages, from harvest to delivery to the customer.”

Cedro notes that as soon as the cherries are picked, the producer begins a “fight against the clock”. His first tip is starting processing as soon as possible.

“Don’t leave the harvested [cherries] in baskets or bags for too long,” he says. “If you do, then uncontrolled fermentation can occur.”

Wet milling

This is the first post-harvest practice, which is where coffees are washed, sorted, and prepared for drying.

For washed processing, cherries will be taken to the wet mill, where they will first be washed and sorted. After that, the skin and mucilage will be removed, before the coffee is subsequently dried.

However, for natural, honey, and pulped natural processed coffees, the process is slightly different. Naturals are sorted and washed clean of any dirt and debris. They are then dried with the skin and fruit still on the bean.

In contrast, honey processed coffees and pulped naturals are sorted, washed, and depulped. After this, they are dried with a varying amount of mucilage left on the bean.

“[Washing and wet milling] is very important for removing impurities and floaters,” Cedro tells me. Cherries that are either underdeveloped or overripe float in water, whereas ripe cherries will sink. 

Washing is sometimes carried out manually at washing stations, by putting the cherries in a tank or a bucket and separating the floaters. Some farms may use a dedicated machine that screens only ripe cherries.

Naturals & pulped naturals

The majority of smallholder coffee farmers in Brazil use natural (dry) or pulped natural processing.

Natural processing is the cheapest way to process coffee, and it is also more environmentally friendly; washed processing produces coffee wastewater, which can be a pollutant. Natural processed coffees typically have a “classic” flavour profile, with a strong body and high sweetness.

In comparison, pulped natural coffees are depulped before drying. Depulping removes the husk and some of the mucilage from the beans. Pulped naturals tend to have a more delicate cup profile, with higher acidity. They also tend to fetch a higher price than naturals.

Nilton Cezar Martins is a specialty coffee producer from Sítio Vô Nininho, also in the Caparaó region of Espírito Santo. He produces pulped naturals. 

“Immediately after harvesting, the beans must be pulped,” Nilton says. “To do this, we peel the ripe cherries and dispose of those that are not ideal for high-quality coffees.”

It is worth noting that not all smallholder producers have access to depulpers, mainly because the equipment is often costly.

Both naturals and pulped naturals can deliver an excellent, high-scoring cup profile, but the choice between the two will largely depend on climate conditions, the equipment available, and the farmer’s preference.

Drying

Whether drying with or without the pulp or mucilage attached, coffees need to be dried until they are ready for milling. According to the International Trade Centre’s Coffee Guide, target moisture levels for green coffee are between 11 and 12%. 

However, the Specialty Coffee Association (SCA) has recently adopted water activity as a primary indicator of moisture in green coffee. Water activity is a complex parameter that is defined by the Food & Drug Administration as the ratio between the vapour pressure of the substance in question (green coffee, in this case) and the vapour pressure of distilled water under identical conditions

According to the SCA’s new standards, water activity in green coffee should ideally be lower than 0.70aw. Water activity increases in line with temperature and humidity, effectively meaning that the principle behind drying remains the same, even if the measurement is different. Furthermore, as this parameter is reasonably new, most producers are still using moisture content as a standard measure at the time of writing.

There are a number of different ways to dry coffee. The most common method is spreading the beans out on drying patios or beds. They should be frequently turned to ensure the coffee dries evenly.

Nila recommends using a cement patio, although some producers use asphalt or other materials.

Nilton says: “It is necessary to dry the beans in a ventilated and heated place, or under sunlight, and to promote a constant heat exchange throughout the beans until all are homogeneous and have the same moisture levels.”

Cedro adds that it’s important to pay attention to cleanliness, too. “You should always dry coffee on clean patios,” he says. “This will help you avoid a cup profile with a ‘dirty finish’.”

Another way is to dry the coffee on raised beds. The method avoids contamination through contact with the soil, and improves ventilation for even drying. 

Aside from drying coffees on patios or beds, some producers also use coffee drying machines. There are two main types of machine that are used:

  • Rotary driers are equipped with a large spinning drum that is attached to a heat source. The coffee has to be pre-dried to some degree before being loaded into the drum.
  • Static driers, however, ventilate and heat cherries mechanically from below. They also rely on a separate heat source to dry the coffees, but unlike rotary driers, static driers can be used to pre-dry cherries.

Dry milling & preparation for sale

Once a coffee reaches the target moisture or water activity level, it must then be dry milled before being packaged and transported.

Dry milling is actually not one process, but rather a number of different processes which prepare the beans for transport and sale. First the beans are hulled to remove the husk (for natural processed coffees) and parchment (for washed, natural, and pulped natural coffees).

Destoners are then used to remove any small rocks, sticks, and any other debris that may have become mixed in during drying. They are then sorted by colour (to remove defective beans), density (using gravimetric tables), and screen size (using a screen to grade and sort the coffees by size).

This process is usually performed in large plants or dry mills, which are typically operated by co-operatives or exporters.

Best practices for dry milling include checking that the machinery is completely clean, and making sure that your coffee is not mixed with another lot, especially if it is a high-quality lot that has been more expensive to produce.

Storage & transportation

Once the coffee has been picked, processed, milled, and sorted, the final step is to package, store, and prepare it for transport. 

Nilton says: “The beans must be stored in suitable and healthy containers and kept in a ventilated area with low humidity.”

He says that for storage and transport, he prefers to use high-barrier bags supplied by GrainPro. “GrainPro high-barrier bags can preserve the chemical, physical, and sensory characteristics of a coffee. They [make things much simpler] for producers and also green coffee buyers,” Nilton tells me

Much like Nilton, both Cedro and Nila also use GrainPro bags. Cedro says that before using them, he had issues with humidity. “It was a game-changer,” he tells me. “Before using GrainPro bags, I had constant problems maintaining my coffee’s moisture content; I was even having issues with mold.”

Nila says that it was during her first specialty coffee harvest that she realised GrainPro bags were important. “The smell is [still] wonderful [during storage],” she tells me. 

“The aroma is [still] strong, very different from the beans kept in ordinary bags. The colour stays perfect, while the coffee beans we have stored in regular bags turn white and lose aroma… it would be impossible to sell them as specialty [coffee].”

Ultimately, improving quality takes time and patience. Diligence throughout your post-harvest practices will eventually lead to greater consistency and most likely improve your cup scores, but it won’t happen overnight. All three interviewees say the results come in the medium and long term.

“You need knowledge, understanding, appreciation of your product, and recognition of the potential of your work and [of] your crop,” Nilton explains. “It takes a lot of care, a lot of patience, standardisation, and constant repetition to reach results you can consider satisfactory.”

For producers, consistency, diligence, and focus are clearly important areas for post-harvest. However, it is important that they also ensure they are able to find a market for these coffees before they set out to maximise quality, as otherwise it could be a potentially risky decision. 

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Please note: GrainPro is a sponsor of Perfect Daily Grind.

Photo credits: GrainPro, Marcionilia “Nila” Venância Ramos, Cedro Fornari, Nilton Cezar Martins

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