A cocoa store is a ventilation problem with a floor

By Johnny Joe, export engineer at Hebei Hongji Shunda Steel Structure Engineering Co., Ltd. · 25 October 2026 · 6 min read

Cocoa arrives at a store in bags, at whatever moisture content the fermentation and drying left it. It then sits there for weeks or months, and during that time it either holds its quality or loses it.

What decides which happens is the air in the store, and the air in the store is a building decision.

Beans are hygroscopic and they are alive

Cocoa beans continue to change after drying. They take up moisture from humid air and release it into dry air, and a stack that sits in still, humid conditions will develop mould at the surface of the bags and, eventually, in the product.

That means the store has to allow air to move through the stack. A sealed building protects the beans from rain and gives them nothing else.

Ventilation is a stack height and opening question

Passive ventilation works when there is a low inlet, a high outlet, and a clear path between them. The height difference between inlet and outlet is what drives the flow, and that difference is a building dimension.

Roof vents, ridge openings and low-level louvres are the components; the building height and the stacking height are what make them work or not. A store with high-level vents and no low-level inlet ventilates its roof void and not its bags.

The floor is where the moisture comes from

A slab on grade in a humid climate wicks moisture, and a bag stack sitting directly on it takes that moisture at the bottom layer. A raised pallet base, a vapour barrier under the slab, or a ventilated floor all address it; a bare slab does not.

This is one of the cheapest details on the project and one of the most consequential, because the loss is invisible until the buyer inspects the stack.

Stack height is a fire and an air question

Stacking higher uses the volume better and reduces the floor area needed. It also reduces the air path between bags and increases the fire load per square metre.

Where a store is designed around a stack height, that number should come from the airflow and the fire strategy rather than from the height of the forklift.

Roof surface temperature matters more than roof insulation

A bare metal roof in the tropics gets very hot, and a hot roof heats the air beneath it, which then rises and draws in humid outside air through the low openings.

That can be an advantage — it is ventilation — or a problem, depending on the outside humidity. A light-coloured roof or a radiant barrier changes the roof temperature and therefore the behaviour, at modest cost.

What I want before drawings

• The quantity of beans, the bag size, and the intended stack height.
• The moisture content at intake and the target at despatch.
• The local climate: whether the store must keep rain out, humidity out, or both.
• The ventilation approach, and whether it is passive or fan-assisted.
• The floor detail: slab on grade, raised, or ventilated.
• The wind speed for the site in km/h from the applicable local code, not a round number — on a store with large permanent openings, the open condition governs.

Cocoa stores are cheap buildings guarding an expensive crop. That imbalance is the whole argument for getting the air right.