Dissertation – Cold Washed Process

Dissertation – Cold Washed Process

by Rasmus Madsen





Once coffee fruits are harvested, the seeds contain a lot of moisture and need to be dried to a level where they can be stored without spoiling. Ideally, this moisture content should be around 10-12% for most species and varieties of coffee. There are various methods for drying coffee, each affecting the flavor and characteristics of the final product. However, since we at Poma® typically are exploring the effects of agricultural practices, we developed a processing method that least interferes with the inherent qualities of the seeds, so that we can evaluate the impact of alterations to the work in the field without any attributes originating from processing. We call this process the ‘Cold Washed Process’ and it involves prohibiting both fermentation and germination of the seeds while drying to avoid any inherent qualities being metabolized or utilized in the process. This ensures the preservation of the inherent attributes of the coffee.

In this dissertation we are exploring the Cold Washed Process as a preservation technique to highlight the natural qualities of coffees, which is a result of its genetics, cultivation environment, and plant management.



Cold Washed Process - Concept

First, the coffee cherries are subjected to an initial cold storage period of 48 hours at 8°C. Subsequently, the cherries undergo thorough depulping and washing of the mucilage, followed by a drying at low temperatures (below 10) in a pressurized, rotating tumble dryer. This gentle and meticulous drying procedure forces the yeast and seed into dormancy, thereby prohibiting both fermentation and germination, ultimately preserving and intensifying the coffee’s inherent aromas and safeguarding its natural profile. Importantly, our cold washed method adheres strictly to the principle of purity. There are no additives, no introduction of yeast or bacteria, and no active fermentation involved—just coffee in its purest form, allowing its inherent qualities to shine through. 


Cold Washed Process – Effect & Data

The preservation, as well as the intensification, of inherent aroma compounds with this processing method, has been continuously verified by GC-MS analysis results. The tendencies show an average increase of intensity of variety unique aromas by 60-70% (table 1), which was measured for the green coffee post-processing. The average preservation of variety unique aroma compounds is above 90% with this processing method, compared to 84±3.6 for the average washed coffee and 67±4.1 for the average naturally processed coffee. It was measured through GC-MS analysis of the green coffee once pre-drying and once post-drying to see the loss of individual aroma compounds during the drying process.

The apparent reason for the greater levels of preservation and intensity of inherent aroma compounds in cold washed coffees, is the retardation of the germination at the low processing temperatures, which allows to retain compounds (free amino acids, fatty acids, oils, sugars, etc.) that acts as precursors for aroma compounds during drying and roasting, which would have been utilized for germination otherwise and end up lost.

Another factor is the absence of active fermentation. Fermentation involves microbial activity that can metabolize certain compounds present in the coffee cherries, including sugars, acids, and other organic compounds. This microbial activity can lead to the breakdown of some inherent aroma compounds through various enzymatic and chemical processes. Additionally, fermentation can promote oxidation reactions that may also contribute to the degradation of inherent aroma compounds. That being said, well-executed fermentation in coffee can be very desirable - introducing a wide range and intensity of new non-inherent aroma compounds to the aroma structure of coffees providing another type of quality. Fermentation also increases the acidity of the coffee, which can be a highly desirable trait, contributing to the brightness and liveliness, balancing sweetness and enhancing overall complexity - a great addition to the diversity of quality coffees on the marked. Fermentation has also proved a great tool to lift the quality of low-quality coffees. However, with the cold washed process, we focus on the genetically inherent aroma compounds, which are typically lost or diluted during fermentation.

At the same time, we typically experience that coffees that have been ‘cold washed processed’ have a higher level of perceived sweetness. This is linked to the aroma compounds being synthesized from the retained aroma precursors, and the already existing aroma compounds in the green beans, are esters associated with fruity sweet flavors and terpenes associated with flavors of sweet florals, which gives off a high perception of sweetness (see table 1).

Some of the key aroma compounds we see in higher concentrations, which are either directly preserved or synthesized to a greater extent, as a result of the cold washed process, include:




Table 1. Preservation and intensification of selected important variety aroma compounds for Caturra subjected to the ‘Cold Washed Process’, obtained through GC-MS analysis of the green coffee pre-roasting. The regular washed version served as the control, and the percentage values shows the increase in occurrence of the individual aroma compounds.  The values for consumer liking, perceived sweetness, and the quality score was obtained post-roasting through a panel of 12 trained professional panelists with 4 sets of repetitions.


Esters

  1. Methylbutyrate: Contributes to fruity aromas, often described as having notes of strawberry or pineapple.

  2. Methyl acetate: Known for its sweet, fruity aroma, methyl acetate adds complexity to the coffee's fragrance.

  3. Isobutyl acetate: Responsible for imparting floral and fruity notes, such as those reminiscent of jasmine or apricot.

  4. Ethyl acetate: Contributes to a sweet, fruity aroma with hints of pear or banana.

  5. Isopropyl acetate: Similar to ethyl acetate, isopropyl acetate adds fruity notes.



Aldehydes

  1. Furfural: Contributes to the sweet, caramel-like aroma characteristic of roasted coffee.

  2. Benzaldehyde: Benzaldehyde adds a nutty or almond-like aroma to coffee.

  3. Vanillin: Often associated with the aroma of vanilla. It contributes to the sweet, creamy, and sometimes floral notes in coffee.

  4. Hexanal: Contributes to green, grassy, or leafy aromas in coffee, particularly in green coffee beans.

  5. Nonanal: Has a fatty and citrusy odor with a hint of orange or lemon.



Ketones

  1. 2-Heptanone: Contributes to fruity and buttery aromas.

  2. 2-Nonanone: May contribute to floral and fruity notes in coffee.

  3. 2-Undecanone: Can add green, grassy, or herbal notes to coffee, particularly in green coffee.

 

 

It should be noted that, overall, the aromas in coffee are a result of the interactions between the coffee plant's genetics, which are the ones we are interested in retaining with this technique, but also the growing conditions (terroir) and roasting technique. Additionally, the overall aroma profile of coffee is influenced by the interactions of various aroma compounds, creating a complex composition of aromas.

It is our desire here at Poma to continue to explore new ways such as new processing techniques to improve coffee quality.