Last year, we focused on celebrating Aida Batlle’s Finca Kilimanjaro as the first farm to do a “process series” and the decade-long collaboration Square Mile has had with her. This modern classic was an early iteration of what is now a common theme in speciality coffee: featuring multiple processes from the same farm. This season, we wanted to explore the fact that Aida and Finca Kilimanjaro are still on the cutting edge of coffee processing. We asked Aida what processes she was most excited about, and she directed us to her experiments with adding cascara tea to the fermentation tank.

What is Cascara?

Fresh cascara from Finca Kilimanjaro after being separated from the coffee seed and husk, at the micromill at J.Hill.

When coffee cherries are “de-pulped,” the skin and most of the fruit is stripped off and separated from the parchment-covered seed. The seed continues on its path to becoming a roasted coffee bean, but what about the peel? Cascara (which translates to “peel” or “husk”) has long been composted and used as fertiliser. In the early aughts, Aida Batlle was one of the first to see that the exceptional care put into ripe cherry selection made this byproduct covetable in its own right. Once dried, it becomes a hibiscus-like substance perfect for infusing into a fruity tea. Companies as large as Starbucks have featured cascara in their beverages.

Cascara from Finca Kilimanjaro is dried with the same care as the coffee itself, preserving the integrity of the flavour compounds within.

Aida’s associates at J.Hill dry her own cascara on shaded, raised beds — just like the parchment itself. QC Director Douglas Chinchilla leads the brewing of a tea with the dried cascara. This tea is added directly to the tank with the de-pulped parchment, influencing the rate of fermentation and allowing the coffee beans to absorb tiny flavour compounds from the fragrant, fruity cascara. Our cascara tea process lot was created specifically for Square Mile, and is available in an extremely limited quantity.

Here are the steps of the process in more detail:

Cherry Intake and Depulping

Bags of coffee cherries from Finca Kilimanjaro, carefully labelled with the section of the farm where they originated along with other details.
The microlot beneficio where Aida’s coffees are de-pulped was originally designed to be attached to the back of a truck. Much like a roasting machine, a smaller-scale wet mill allows for more precision despite less economy of scale.

Like all of Aida’s coffees, the cherries from Kilimanjaro undergo intensive manual selection–indeed, they are some of the most uniformly ripe that we’ve seen. They’re carefully labelled with key lot info and driven from the farm down to the micromill at J.Hill specifically used for these smaller lots. Following several floats to remove lingering low-density cherries, the coffee is de-pulped and flows into fermentation tanks. Each ceramic tank in the micromill holds up to 10 ~69 kg bags of cherry, de-pulped. This is a very small tank size and allows for very specific and contained processing on small lots.

QC Lead Douglas Chinchilla and another J.Hill employee prepare to pour the cascara tea into the mill’s small fermentation tanks.

Adding the Cascara Tea

Dried cascara brewed as tea is strained through a sieve fashioned out of a bucket. The extra sugar and aromatic compounds affects the flavour development happening within the fermenting coffee below.

Aida and Douglas have been experimenting with the cascara tea washed process since 2012. Warm cascara tea (using cascara from Finca Kilimanjaro, of course) is added to a wet fermentation (water from de-pulping stays with the parchment rather than being drained).

Much like the fruit-additive processes that are currently in vogue, the fragrant chemical compounds from the fruity cascara can penetrate the cell membrane of the bean and be uptaken, adding interesting flavours to the final cup. Adding this tea to the fermentation tank also provides extra sugars to lure microorganisms that make fermentation possible. 

Unlike other additive processes using fruit or spices, this cascara comes from the coffee, maintaining Aida’s ethos that all flavours should come from the contents of the coffee cherry itself.

Temperature and pH for every lot are monitored, and the lot is taken out of the tank based on these metrics, not necessarily how many hours it has been in the tank. This is an effective approach because the tanks are open to the elements, so the ambient temperature and humidity can cause big differences in fermentation rate from one day to the next. 

After Fermentation

Post-fermentation, the coffees are rinsed and receive the same attention to detail that J.Hill gives to all Aida Batlle coffees. Careful, shaded-bed drying, meticulous dry milling, and traceability as the coffee moves from tank to drying bed and to the warehouse. 

Now in the UK, we can attest that they show the same elegance in the cup that we’ve come to love from all Kilimanjaro coffees.




tasting notes


Jamie Isetts

Jamie Isetts manages Square Mile's green sourcing program from her adopted home of Austin, TX. She travels the world to learn from farmers and roasters alike but also makes a pretty great spreadsheet.

Jamie Isetts

Jamie Isetts manages Square Mile's green sourcing program from her adopted home of Austin, TX. She travels the world to learn from farmers and roasters alike but also makes a pretty great spreadsheet.