The phrase “monsooned coffee” refers to a method of drying green coffee. The coffee "bean" as we know it, is actually the seed of the coffee fruit. That fruit is picked at its ripest red state. Then the "seed" or "bean" has to be extracted out of the fruit. Depending on where the coffee farm is, and the access to water will determine the method used to remove the bean from the fruit. In areas where there is greater access to water (South and Central America for example) will use a method called "Washing" where the beans float down a trough, through a mill that removes the seed (which then sinks) and the fruit floats on down the trough. In areas with low access to water (East Africa for example) coffee is "dry milled".
Once milled, the coffee beans need to be dried out so that they will not mold in the bags. This is usually done on large concrete pads in the sunshine, or on suspended tarps. This is where "monsooned" coffee comes in. Usually at this step, if the weather will turn and start to rain, the green coffee is collected and brought into storage. Monsooned coffee however is allowed to be exposed to the "monsoon". The green coffee will absorb rain, thereby increasing its moisture content and then dried out again. This results in an additional fermentation process which adds an interesting, almost spiced flavour profile to the coffee.
On occasion, this technique has been used to mask certain negative qualities in green coffee beans. Especially when a coffee has been allowed to over-dry (reducing the moisture content below 9%) usually by accident. These coffees are exposed to the rain to increase moisture content and density of the green coffee, and thereby increasing the weight of the coffee (as coffee is sold by weight, this method means more money for a coffee farmers crop).
Monsooned coffee has a very unique taste, and usually ends up in a blend as the taste as a single origin monsooned coffee is a little to intense and pungent for even the most seasoned coffee cupper.