The Zero Waste Coffee Project

On the valorization of coffee by-products: solid state fermentation and distillation

Presented by Chad O’Neill, Master Distiller of VILE CORP, Ontario Canada.

6 July 2019, published  on November 4.2021

Abstract:

We present a novel method of beverage alcohol production from coffee pulp that is accessible at minimal cost and complexity to farmers and uses no additional water. The waste matter from this process may be used to start edible mushroom cultures or biogas recovery and promises to fully remediate the coffee waste.

Introduction:

The need to increase the revenue from coffee production is important in this competitive commodity market, as is the need to minimize ecological damage caused by processing this crop. 

“418 bottles of 750mL 40% alcohol could be produced per hectare of land assuming 1.44 ton of coffee is produced per hectare.

- Galanakis 2017 “Handbook of Coffee Processing By-Products - Sustainable Applications” p227

This number is based on the sugar content of the by-products and reflects the potential amount of alcohol that can be produced per crop hectare; in growing areas with higher or less trees/ha that number increases or decreases accordingly. This is using the traditional Western methods of fermentation in a liquid, which require the use of large fermentation vessels that can hold water and the use of large distillation vessels that can hold this liquid under pressure. 

VILE CORP has developed a continuous distiller that negates the need for a large distillation vessel since it can run fermented liquid through a machine which splits the fermented liquid into water and alcohol of 50%-60% alcohol by volume (ABV) which can then be transported to a facility for re-distillation, purification, bottling etc. The continuous distiller runs on 10,000watts of power, has a footprint of 60cm by 90cm and is about 1.8m tall. It can output 20L-25L an hour of 50%- 60% alcohol from a fermented liquid at 12% ABV which must be free of solids.

This machine requires training to run and at an investment of $20,000 CAD, may be out of reach of many farmers. There is also the concern of requiring large fermentation vessels as well as pumps and filtration systems.

Scaling up alcohol production to a size that individual small farmers can afford seems to be a major concern. Convincing small farmers to purchase fermentation and distillation vessels would likely require subsidies from government or development agencies. It seems that rather than increasing capital investment by farmers it would be more efficient to increase labour costs. Since much coffee production occurs on slopes which deter mechanized production methods in favour of human (by hand) production methods, let us continue in this vein.

Methodology:

The most widely consumed alcoholic beverage in the world is called Baiju and it is produced and entirely consumed in China using ancient rustic methods that directly apply to our coffee fermentation concerns. These methods involve labour costs and are very low in machinery costs. In addition they are very low in water consumption and there is no need for a water-tight fermentation vessel nor for a complex distillation apparatus.

For more information on Baiju production please refer to

https://www.sciencedirect.com/science/article/pii/S0924224416303995

The following is a simplified description of fermentation/distillation of coffee production byproducts using a process similar to that of Baiju:

Immediately after depulping, the pulp of cherry skins, mucilage and any other fermentable products available is to be combined with wine yeast*that has been inoculated in great quantity onto another solid substrate such as rice hulls, vermiculite and previously inoculated pulp. This pulp can be mixed by hand or by landscaping machine into a mound atop a shallow pit lined with heavy plastic or another inert material. Once properly stirred and the moisture content is deemed correct, it will be covered completely with heavy plastic and weighed down around the edges to prevent oxygen ingress.

Solid-state fermentation is basically an anaerobic compost mound where the active microorganism is yeast.**

The yeast will ferment the available sugars, producing CO2 that will escape through a lock in the top of the plastic. The yeast will produce ethanol that will soak into the solid substrate along with the water.

When this fermentation is finished the top layer of plastic will be removed and replaced with a cylinder of sheet metal that encircles the entire mound. The cylinder is topped with a tight fitting lid shaped like a cone that leads to a condenser that will cool the alcohol vapour. This apparatus resembles a flat- bottomed grain silo. Steam from an external boiler will be injected into the cylinder, heating the substrate and causing the alcohol to vaporize and rise out to be cooled by the condenser.

The alcohol will be collected in barrels and transported to a central distillery for re-distillation, purification and bottling.

The remaining substrate of pulp has now been sterilized, de-sugared and had a significant portion of its nitrogen removed. This will greatly reduce the oxygen demand, limiting pollution. It can be shovelled out as a solid rather than pumped as messy slurry. But in fact at this point it becomes an ideal substrate for growing mushrooms***.

Alternately, rather than attempting mushroom production, the farmer could produce biogas**** with the same silo apparatus, provided the relatively high investment costs can be covered. This gas could then be used to fire the boiler, other equipment or converted to electricity.

Notes:

The solid-state method described is optimal for a mechanical separation method that limits the amount of water used in the separation process. If the mechanical separation method splits mucilage from skins, this provides better control over the process but it should not be necessary.

·     Alcohol production will work with the wet method of coffee processing if we can limit the amount of sugar lost to the wash water and prevent natural fermentation from beginning.

·     Alcohol production will work with the dry method since there is enough dried mucilage and sugar on the waste that is removed from the dried beans.

·     The solid-state method described seems optimal for the honey method of processing. If some mucilage is gently rinsed or steamed off the wet beans before they are dried, this sweetened water would also be valuable in the solid-state method.

·     Water that has been used to float and wash the whole cherries can be reused as boiler water to generate steam and as cooling water to condense the alcohol. Cooling water can then be reused to wash cherries.

·     Simple chemicals such as potassium metabisulphite should be used at different points in the production process to prevent wild yeasts and bacteria from infecting the substrate

·     A major advantage to the solid-state fermentation process is that the farmer does not need to move the pulp between vessels. He brings the vessel (silo) to the mound of pulp. This means that the silo can be moved each day to a new mound, processing them each in turn, and the farmer would only need a small number of silos depending on the size of his daily pulp output.

·     The farmer can be paid based on the amount of alcohol he delivers and on the amount of mushrooms he produces. These are tangible products with immediate return.

·     The barrels of alcohol delivered to a central distillery can be refined into a unique and pleasant alcoholic beverage that will expose the world to a completely new kind of spirit. Not only would a coffee growing country show itself at the forefront of permaculture and sustainable agriculture, but also it would be possible for the country to create an Appellation of Origin control similar to how only Mexico can produce Tequila and only one region in France can produce Champagne. This requires that that country spearhead the production of this Cascara spirit and be first to the world market with this beverage.

·     VILE CORP would dearly like to be instrumental in making this happen. We would be happy to visit a coffee plantation and develop a pilot production facility to prove the efficacy of solid-state fermentation and distillation.

*https://www.sciencedirect.com/science/article/pii/S0306261911005162

**http://www.biochemsoctrans.org/content/17/2/424

***https://www.researchgate.net/publication/267935608_MUSHROOM_CULTIVATION_ON_COFFEE_PULP_
Commercial_production_and_marketing_of_edible_mushrooms_cultivated_on_coffee_pulp_in_Mexico

****https://www.sciencedirect.com/science/article/pii/S0196890413003889

See also: https://www.sciencedirect.com/science/article/pii/S0023643813002065