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Solar Spectrum Fermentation: Year 3

It’s been a minute since we looked at our solar spectrum experiment with Daterra in Brazil. If you are not familiar with this, it is where we have been seeing the impact that colour has on the fermentation of coffee. We are now in our third year, with the second year progressing from visible light to the wider spectrum (UV and Infrared), producing interesting but confusing results. Year three is a repeat to validate what we got or not.

Cupping of the plot is conducted both by the team at Daterra and DRW. We do this separately, and then compare the results. Here, the advantage of the Ikawa comes to the fore -we can set identical profiles to reduce roast variability.

There are now two stages to the experiment: one that filters sunlight via coloured boxes the coffee is fermenting in, and the other in blue barrels to block out the sunlight, which are then fitted with a range of lighting internally.

Repetitions have allowed us to knock out the outliers and amalgamate results from both sides over the three years. This allows us to get a glimpse of the overarching patterns of colour and what effect light wavelength may have on flavour.

This year (2023 crop) we trialled red light, blue light, Halogen, infrared and grow lights (144 LED) in the barrels. Fermentation was anaerobic for 72 hours. The boxes, as usual, were red, yellow, green, blue, transparent and black. We use Arara, a yellow varietal, and picking was September 22nd.

Coloured Boxes

This year, red again came top with a score of 87.14. Yellow was second with 85.82, transparent 85.67 and black 85.40. For those who remember the first experiments, transparent and black were the worst performing, so it shows the values of repetition. The lowest score for the set was 83.77.

There has also been discussion of preferences too, with flavour biases perhaps interfering with a teams result. This is reduced year on year, this year with DRW scoring black above transparent, and Daterra scoring yellow and green the worst.

Artificial Lighting

For the artificial lights, Infrared edged it by .06 against Red halogen. However, the halogen had two instances: 72-hour fermentation and 90-hour fermentation. Comparing the same times, infrared was the clear winner with a 1.07 difference in score. The full lineup was infrared, red halogen (90hr), blue halogen, red halogen (72 hr), no lamp and LED grow lights last. The lowest score here was 86.71, and the highest was 88.24.

Pulling it all Together

What can we say over the three years that this has run then? Starting with a 60-hours fermentation in 2021, we have expanded times from 48 hours to 90-hours fermentation. In 2022, we increased this to include the longer wavelengths, too, as there already exists information about UV and the protection of coffee from that. As red was the higher scoring end of the spectrum too, it made sense to concentrate on this area.

By combining all of these results (huge thank you to Diulie from Daterra for doing this for us!), here is what we can say so far.

Coloured Boxes Results

Red is the overall winner here. A combination of both teams over three years left us with an average of 86.42. Yellow was half a point behind, closely followed by blue. Transparent and Black then follow, with green rounding the spectrum out with 85.50 points. This means the spread is just under a point in difference. See the full table below:

2022 results combine the scores of the three time differences in fermentation.

Artificial Light Results

In the last two years (2022 & 2023), the Halogen light has proven to be the best, but with caveats around time. The table below shows that red and blue halogen at 90 hours and 72 hours, respectively, have the highest scores. However, the table only includes results from one year. In 2022, we tested at 60 hours and 72 hours of red halogen fermentation, and like for like, the infrared won; against the blue halogen, though, infrared would still take second place.

Whilst it may be tempting to jump to a firm conclusion on this, it is too early to conclude anything firm. Some iterations could benefit from being repeated, and they absolutely will be! There is however a parallel to this -red netting used for shade cover in nurseries has been found to be beneficial to seedlings, producing beneficial effects for root length, fresh matter and dry matter. It would be great to think we are seeing a similar story here.

Coffee is rarely about revolutionary steps, but being able to add 1-2 points to the score of a coffee could be a huge gain. However, for those that have been around long enough to remember the Caturra vs Castillo in Colombia, there is a note to mention on flavour too. Red has also produced a more complex set of flavour notes from a calibrated team. It should be fun to develop this line of thinking, too, but as with any experiment, it can be hard not to run away with possibilities. The idea of being able to adjust flavour profile slightly towards a particular audience is an intriguing one though.

Colour treatments are on the left, with aromas followed by flavour descriptions.

The experiments will continue with the 2024 harvest. Questions still exist around flavour, skin colour of the varietal and what to do with it. There is of course another experiment running in the background to this that will hopefully allow us to tie things up in a neat bow. Perhaps for now though, a good place to end is in the acknowledgement that without people like Daterra who allow others to experiment on their farm with their expertise, none of this would have been possible. Our thanks go to the team!