What Are the Three Major Variables Affecting Coffee Processing: The Connection Between Coffee Fermentation and Coffee Processing Methods

In coffee, the terms we hear most often are the processing methods themselves: washed, natural and honey. These three traditional methods are familiar territory for most drinkers. What gets discussed far less often is what actually decides whether they succeed.

FrontStreet Coffee wants to look at the three variables that sit behind every processing method, because no method works on its own.

1. Cherry Quality

Good coffee cherries are the foundation of good coffee. If the cherries are poor, whether unripe or overripe, even the most meticulous processing will be wasted. The cup will show off-notes, astringency and outright faults such as grassy, cardboard or rotten-fruit flavours. The trouble is that most pickers worldwide are paid by the quantity of cherries they bring in each day, not by quality, so there is little incentive to take only the ripe fruit. Harvesting the fruit properly, the very first step in quality control, therefore matters more than almost anything that follows.

2. Fermentation Control

Traditional washed processing demands large volumes of water, which is why it is also called wet processing. Water is used at four points:

First stage: harvesting the coffee cherries

Second stage: removing the skin and using water flow for an initial grading

Third stage: moving the depulped fruit into fermentation tanks

Fourth stage: completing fermentation and the subsequent washing stages

The purpose of the washed method is to ferment away the mucilage still clinging to the parchment before the beans are dried in the sun or by machine.

How long fermentation runs depends on the region, the ambient temperature and the condition of the tanks. A short fermentation may finish in a single night, while a long one can stretch to 36 hours. Natural processing, Brazilian pulped natural and honey processing all require the same kind of control.

Natural processing dries the whole fruit, and honey processing keeps the mucilage layer, but both still have to manage the fruit, and fermentation continues through processing and drying. The sugars and moisture in coffee cherries are unstable during this period. Typical failures in traditional natural processing are pungent, low-grade alcoholic notes and rotten, overripe fruit flavours.

Setting aside defects that were already present in the cherry, many negative flavours come from poor fermentation management during drying. Honey processing can also ferment badly, or even spoil, when humidity is uncontrolled, when the beds are mishandled overnight, or when rain catches the crop. Managing fermentation well, and understanding how the degree of fermentation shapes flavour, is central to controlling green bean quality.

3. Drying

Four things matter when managing the dry:

"How long drying lasts"

"Whether drying is even"

"Temperature control in artificial drying"

"Airflow and ventilation"

Under-drying leaves too much moisture activity in the bean, while over-drying bleaches the beans pale white and strips away flavour. Both directions hurt the cup, which is why the moisture content of the beans is so important.

These three processing methods have spawned countless variations. Whatever the method, the aim is the same: to draw out the character of that style. Understanding how coffee is processed is what lets us appreciate each cup, and glimpse what people call "the God in the cup."

FrontStreet Coffee Recommendation

FrontStreet Coffee's Cerrado is a clean illustration of a pulped natural, the ancestor of the honey family. The skin is removed and the beans are dried with some mucilage still attached, which shortens drying time while avoiding the off-flavours that sloppy fermentation can create. The classic Brazilian profile comes through clearly: cream, peanut, nuts and chocolate.

FrontStreet Coffee's Costa Rica Black Berry takes the idea further with a black-honey process that removes almost none of the mucilage. Drying runs longer, at least two weeks, with covers used to slow the sun so the sugars convert fully, and the beds are turned at intervals so no pocket ferments too far. Given a medium-light roast, the ground coffee releases an intense floral aroma, and the cup shows grape, berries and ripe blackberry.

FrontStreet Coffee's Costa Rica Mozart uses a raisin-honey variant, a modern take on the traditional yellow, red and black honey styles. The whole fruit is pre-dried on raised beds for at least three days before the skin and pulp are removed and the honey steps continue. Keeping 100% of the mucilage makes this harder to control than black honey, and the payoff is a richer, riper fruit sweetness: osmanthus, pineapple and raisin, whether brewed as pour-over, cold brew or in a moka pot.