Refs:
Trianoncoffee - how-is-honey-processed-coffee-different-from-washed-or-natural
Barista Magazine - The Costa Rican honey process
Red Cedar Coffee - The-honey-process-explained
A great YouTube video of the process https://www.youtube.com/watch?v=k5iw31z1FAY
Coffee Chronicler - Other processing methods
The Honey Process
There are generally three grades of honey-processed coffee, referred to as yellow, red and black.
When most (but not all) of the mucilage is removed, as the coffee is drying, the sticky coating on the outside of the beans oxidizes and darkens in color and the resulting bean is referred to as yellow honey. This is also referred to as semi-washed.
When about half is removed and the coffee is allowed to ferment longer, the mucilage further oxidizes to a red color so the resulting bean is referred to as red honey.
When virtually none of the mucilage is removed after de-pulping and the coffee is allowed to ferment longer, a darker colour develops and the resulting bean is referred to as black honey.
In most cases at most mills who have tried honey-processing, the different grades are achieved by mechanically removing varying amounts of the "mucilage" before putting the sticky beans out to dry.
But at least one coffee producer does it differently.
At Lajas where the honey process began in earnest, they leave 100 percent of the mucilage on the coffee after de-pulping, and control the color through refined fermenting and drying methods instead.
Honey processing is more risky than normal fully de-pulped and washed green bean processing because coffees with any amount of fruit left on them are susceptible to mold, over-fermentation, and other processing risks.
Unlike processing the "clean" green beans, the ones which carry pulp with them are also much harder to process because the sticky fruit will often clog the machines, so mills need to stop regularly for cleaning, to remove the build up of material left in the hullers.
Probably the greatest benefit to producers who tackle honey-processing, is that the process uses much less water.
Allowing fruit to dry on the bean means it can be removed during milling instead of being washed off after de-pulping the way washed coffees are processed.
Although the type of bean plays a significant part in the resulting coffee flavour, the following broadly describe what to expect from honey processed beans.
The Yellow honeys typically have a subtle fruitiness but are not far removed in taste from washed coffees.
Red honeys tend to have a sort-of red-fruit sweetness with some nutty undertones.
Black honeys have a kind of raisin-like sweetness and give a full sensation in the mouth with dark chocolate and nut-like flavours apparent as well.
Yellow honey processed coffee is turned more often to encourage drying, while red and black are turned less often to encourage controlled fermentation.
It is the length of that drying process which allow the coffees to develop more or less fruity flavors.
Non honey processed - washed green beans
Yellow beans are immediately laid out under the sun in a thin layer and turned regularly to encourage rapid drying.
Yellow honey - up close ... and drying
Red and Black are heaped for differing times while undergoing aeration and agitation before being raked out to dry
Red Honey - up close ...
... and red / black
preparing for spreading
for final drying
Black Honey - up close
Other Processes
The Natural Process
The Washed Process
The Carbonic Maceration Process
Acetic & Lactic Processing
Double Fermentation - Kenyan Processing
Wet Hulled Processing
Monsooned Malabar