Inside a Monsooning Warehouse

Monsooning is done in purpose-built warehouses on India's south-west coast, in Kerala and coastal Karnataka, during the south-west monsoon between roughly June and September.

The buildings are unlike anything else in coffee. They are open-sided, with wide eaves and slatted or louvred walls, designed so that monsoon air moves through continuously while rain does not reach the floor. They exist to admit weather in a controlled way, which is the opposite of every other coffee store.

The sequence

Selection. Not every lot is suitable. The coffee is already cured green — hulled, graded, sorted — from the preceding harvest. Cherry-processed lots and robusta take the process better than delicate washed arabica, which has character to lose and little to gain.

Spreading. The green coffee is spread on the warehouse floor in a layer of a few inches. Too thick and the middle heats and moulds; too thin and the floor space runs out.

Exposure. Monsoon air, saturated and moving, passes over and through the layer. The beans take up moisture and begin to swell. Colour shifts from blue-green towards pale gold.

Raking. The beds are raked at intervals — turning the mass so every bean gets equal exposure and no pocket sits damp and still. This is manual, repetitive, and it is the main labour of the operation.

Bagging. After the initial exposure the coffee is put into loosely filled jute bags and stacked in rows with gaps between, so air continues to move through the stack.

Re-bagging. The stacks are broken down, the coffee emptied, re-bagged and restacked — repeatedly through the season. This prevents compaction, redistributes moisture between bags, and is why monsooning is labour-intensive rather than merely slow.

Re-grading. At the end, the swollen beans are screened and sorted again. Size and density have both changed, so the pre-monsooning grade no longer describes the coffee. See Indian coffee grades.

Drying back. Moisture has to come back down to a shippable figure before the coffee can be bagged for export.

What the operator is controlling

Three variables, none of them precisely:

• Layer depth, which sets how evenly air reaches the beans.
• Frequency of raking and re-bagging, which prevents hot spots and compaction.
• Total duration, judged from the coffee rather than a clock — several weeks, dependent on how the monsoon behaves.

That last point is the honest limitation of the process. A weak monsoon produces weak monsooning, and there is no way to compensate. It is agriculture applied to a warehouse.

What can go wrong

Mould. The coffee is deliberately being made damp in a warm, humid building. Insufficient turning, too deep a layer, or a stagnant corner produces mould, and mould in monsooned coffee is a serious defect rather than a cosmetic one.

Uneven monsooning. Beans that sat in the middle of an unturned stack are less monsooned than those at the edge. The lot then has two populations that roast differently.

Insects. Warm, humid, open-sided buildings full of grain are attractive. Managing that without chemical intervention is part of the operation, and worth asking about on a certified organic lot.

Over-monsooning. Pushed too far the coffee goes past characterful into flat and woody, with a musty edge that is a defect rather than a feature.

What to ask a supplier

• How many weeks of exposure this lot received.
• Which monsoon season — and how that monsoon actually was.
• Post-monsooning grade, not the pre-monsooning one.
• Moisture at shipment, since moisture went deliberately up and must come back down. See moisture content and water activity.
• How the warehouse manages insects, particularly on certified lots.

A supplier who answers all five has controlled the process. One who answers "it is monsooned" has bought it from someone who did.

Why it survives

It would be reasonable to ask why anyone still does this, given it is labour-intensive, weather-dependent and produces a coffee with less acidity than it started with.

The answer is that it produces a flavour nothing else produces, there is established demand for it — particularly in Italy and Germany — and India is the only origin that can supply it. That is a durable commercial position, and it is rarer than it sounds.

Hoysala monsoons in its own dedicated unit. That matters for the reasons above: layer depth, raking, re-bagging and duration are judged by the same people who grew and cured the coffee, rather than handed to a warehouse working to somebody else’s schedule.

What the process does to the cup is covered in what is monsooned Malabar.