Experiments in Coffee Drying and Quality


At Aldea Development's coffee processing and training center (the beneficio), we are always trying to learn more so we can share that knowledge with coffee farmers. During this past harvest, we conducted a coffee drying experiment with the support of Michigan's Spring Lake Rotary. Below is a report on the experiment:

Goal

To give advice to farmers on the best method for drying their coffee, to get a higher quality coffee and therefore a higher price from selling to Aldea Development.

Introduction

Before the drying experiment can begin, picked coffee is processed to remove pulp, and then it is fermented and washed. These steps remain important for obtaining a high quality coffee, but the next step of drying can particularly affect quality and how long the coffee stays good. By experimenting with how drying affects quality and longevity of coffee, we can better advise the farmers in our programs.

Preparation

There are two main ways small-scale farmers dry their coffee: on patios and in solar dryers. We built a small patio so that we can replicate patio drying, and we built a shaded area to cool coffees once they had finished drying. We also purchased humidity meters to get exact readings of the coffee humidity throughout the process.

Method

We took a single-source coffee (purchased from Cecilio Vasquez of La Unión) and depulped, fermented, and washed all of the coffee.

For the drying, we separated the coffee into different trials, varying the following:

  • Thickness: The thicker the coffee is spread when drying, the slower it dries. So, adjusting thickness allows us to control the total drying time.

  • Drying apparatus: We used a solar dryer and a patio for drying.

  • Sun/shade: By drying under shade, there is no direct sunlight hitting the coffee, which can potentially affect the flavors.

Results

For this drying experiment, we did a total of 6 trials. The fastest-drying coffee was dried in 75 hours, while the slowest-drying coffee was dried in 220 hours. (See graph below.)

Current stage

Before coffees can be tasted, they must rest for a minimum of 30 days after drying, or they will have a vegetal flavor (common to all coffee). We have just reached the end of this phase and are preparing the samples for tasting.

Future work

We are working with a panel licensed Q graders (the highest level of coffee evaluation certification), which will be evaluating the coffees. We will taste the coffees every 3 months and compare this to the data collected during drying to evaluate how the quality changes over time of the different trials.

An initial tasting showed results scoring from 79-82.5 using the Specialty Coffee Association of America cupping evaluation format, with the drying method affecting the sweetness, body, acidity, and balance of the different trials. Further results will be reported once the coffees have been tasted by the panel of Q graders.

Table 1:

Table 2:

Table 3:

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Aldea Development is a 501(c)(3) nonprofit organization.