Ground coffee silos and degassing

Grinding completely changes the way coffee behaves. A much larger surface area is exposed, carbon dioxide continues to be released, and the product becomes particularly sensitive to oxygen, moisture and temperature.

The time between the grinder and the packaging machine is not simply a waiting period. It is a process stage that affects aroma preservation, dosing consistency and the subsequent behaviour of the package.

At TecAIRE, we design and manufacture ground coffee silos to manage this stage within industrial coffee lines. Each installation is configured according to the product, production capacity, available space and packaging format.

Carbon dioxide generated during roasting remains trapped in the porous structure of the coffee. Once the coffee is ground, the increased surface area facilitates its release. At the same time, the product loses aromatic compounds more quickly and becomes more exposed to oxygen.

Fórum Café explains that gas retained after roasting continues to have an effect during grinding, storage and packaging. The publication also highlights the importance of degassing for formats such as vacuum packs and capsules.

The silo creates a buffer between the grinder and the packaging machine. It receives the coffee, keeps it protected and enables a continuous supply to the dosing unit. The challenge is to release the necessary gas without unnecessarily extending residence time or encouraging aroma loss.

Asking how many hours coffee should remain in the silo may seem straightforward, but the answer varies with each product. It is influenced by origin and blend, roast degree and profile, particle size, temperature and package type.

A capsule, a vacuum pack and a valve bag can accommodate different amounts of residual gas. In vacuum-packed or single-serve formats, excess CO₂ can deform the package or affect the seal. A one-way valve, by contrast, allows some of the gas to escape after sealing while limiting oxygen ingress.

For this reason, TecAIRE recommends defining residence times using samples and tests with the actual coffee. Automatically applying a value used for another blend or package can lead to incorrect sizing.

Capacity is only one part of the design. It is also necessary to examine how the coffee enters, how long it remains, how it is discharged and what happens when the packaging machine stops.

FIFO operation helps prevent batches with very different processing histories from remaining in the system together. Extraction should minimise retention, compaction and particle segregation. Conveying to the silos and from them to the packaging section can be pneumatic or mechanical, depending on the installation requirements.

In certain applications, inert atmospheres or other solutions can also be used to limit contact between the coffee and oxygen. Their necessity must be assessed according to the product, process and packaging system.

Variations in the coffee quickly reach the packaging machine. If bulk density, fines content or flowability change, the volume occupied by each dose may also change.

For capsules, where space is limited and repeatability is particularly important, particle size, packing density, particle shape and behaviour in relation to moisture should be controlled. Fórum Café identifies these variables as relevant to filling and extraction.

The silo cannot correct inconsistent grinding on its own. Its contribution is to provide stability when industrial coffee grinding, conveying, storage, discharge and dosing systems have been designed as parts of the same line.

TecAIRE designs and manufactures storage systems for green, roasted and ground coffee. For ground coffee, the configuration is engineered to integrate with the grinding section and the packaging feed system.

Depending on the project requirements, the installation may include:

• Receiving from the grinding section.
• Pneumatic or mechanical conveying to the silo bank.
• FIFO operation without forced coffee movement.
• Cubic silo configuration.
• Pneumatic or mechanical conveying to the packaging section.
• Control via PLC and HMI screen.

These features form part of the product range published by TecAIRE. Capacity, materials, degree of airtightness, instrumentation and level of automation are defined for each project.

Before sizing the system, five questions should be defined:

1. Which coffees, roasts, particle sizes and formats will be processed.
2. How much residual gas each type of package can accommodate.
3. How the coffee’s density, temperature, moisture and flowability vary.
4. What usable capacity is required by the relationship between grinding, storage and packaging.
5. How cleaning, product changeovers and line automation will be managed.

Product trials and process validation help confirm residence time, package behaviour, dosing repeatability and sensory results before final sizing.

A properly specified silo is not passive storage. It partially decouples grinding and packaging, absorbs minor production variations and supplies the line more predictably.

When residence time, discharge, conveying and control are designed together as part of an integrated coffee processing line, the system can support aroma protection and more stable dosing.

Testing is advisable before finalising the design. Package behaviour, dosing repeatability and the result in the cup provide more useful information than applying a standard time taken from another line.

No. The decision depends on capacity, grinder operation, packaging-machine demand, packaging format and the degassing time validated for the product.

No. The coffee, roast, particle size, temperature and package type affect the permissible amount of residual gas and the time required.

They manage coffee between grinding and packaging, provide the residence time required for degassing and coordinate grinder output with the demand of the packaging lines.

Yes, provided that capacity, distribution, recipe separation and control systems are designed for this operating method.

No. An inert atmosphere can help limit the coffee’s contact with oxygen, but the degassing process depends on product behaviour and the overall installation design.

1. Samo Smrke, “La ciencia de la frescura del café” [The science of coffee freshness], Fórum Café, no. 84.

2. “La desgasificación del café: ¿qué, cuándo, cómo y por qué?” [Coffee degassing: what, when, how and why?], Fórum Café, no. 77, pp. 33–35.

3. “Válvulas de desgasificación” [Degassing valves], Fórum Café, no. 96, p. 46.

4. “La granulometría del café” [Coffee particle size], Fórum Café, no. 85.

5. TecAIRE, “Silos” product page. Source for corporate product statements.