CA (Controlled Atmosphere) Storage in Warehouse Logistics

Guide & Lexicon: CA Storage (Controlled Atmosphere) in Logistics

If you want to store fresh products such as apples, pears or cabbage for months without any loss of quality, conventional cold storage systems quickly reach their physical limits. The solution to this challenge in the modern supply chain is called CA (Controlled Atmosphere) storage. But what looks like fresh fruit to the consumer in the supermarket requires highly complex logistics real estate, massive investments (CAPEX) and the highest level of expertise in contract logistics in the background.

What is a CA warehouse? (Definition & Functionality)

The abbreviation CA stands for Controlled Atmosphere. It is a specialized warehouse logistics process in which not only the temperature and humidity are regulated, but the composition of the indoor air is specifically changed.

Normal breathing air consists of about 78% nitrogen and 21% oxygen (O₂). In a CA warehouse, the oxygen content is drastically reduced to values between 1.0% and 3.0%, while the carbon dioxide (CO₂) content is slightly increased. The goal: The "breathing" of the stored fruit is reduced to an absolute minimum. The biological clock of the products is virtually stopped, which extremely slows down aging processes, rot and the breakdown of vitamins.

The technology: Optimal control of oxygen, CO₂ and temperature

In order to create such an atmosphere in a logistics hall and maintain it permanently, highly complex plant technology is required:

1. Nitrogen generators: They flush the room with nitrogen at the beginning of storage in order to actively displace oxygen from the hall.
2. CO₂ adsorber (scrubber): Since fruits still breathe minimally even in the "sleep state" and release CO₂ in the process, excess carbon dioxide must be regularly filtered out of the air (washed) to avoid suffocation damage to the product.
3. Ultrasonic humidifier: To prevent the goods from drying out and losing weight during continuous cooling, the humidity is kept constant at 90 to 95%.

Structural requirements for the logistics property (CAPEX)

From the point of view of real estate development, a CA hall is the absolute premier class of refrigerated logistics. The construction requires a massive capital investment (CAPEX), as conventional insulation standards are not sufficient here.

The most important structural criterion is absolute guest tightness. If the artificially created gas mixture escapes or oxygen penetrates from outside, the entire harvest is at risk. The walls and ceilings of the logistics property consist of special, highly insulating sandwich panels, the joints of which are sealed gas-tight several times (e.g. with permanently elastic special paints). The industrial floor is also given a special gas- and vapour-proof coating. Access to the hall is via heavy, often hydraulically sealing CA special doors, which are also equipped with a small viewing window (porthole) in order to be able to visually inspect the goods without opening the door.

CA Warehousing in Contract Logistics: Business Model & OPEX

For contract logistics companies, operating a CA warehouse is a highly profitable, but also risk-prone niche. The business model is strongly seasonal – the halls are filled at harvest time (e.g. in autumn) and often only gradually emptied months later.

The operating costs (OPEX) are enormous. In addition to the high energy costs for permanent cooling, the operation of the gas generators and the constant sensor-based monitoring of the parameters have an impact. Successful logistics service providers offer valuable value-added services (VAS) here: After opening the CA cells, they take over quality control, final sorting, packaging into supermarket-compatible packaging and just-in-time distribution (outbound logistics) to retailers.

ULO and DCA: The next level of warehouse logistics

The market for CA storages is developing rapidly in terms of technology. Today, logisticians often encounter two extended terms:

• ULO storage (Ultra Low Oxygen): In this case, the oxygen content is reduced even further to below 1.0%. This requires an even more extreme hospitality tightness of the property.
• DCA (Dynamic Controlled Atmosphere): This is the most modern form. Here, sensors (e.g. via chlorophyll fluorescence) measure the "stress level" of the stored apples in real time. The logistics IT dynamically adjusts the oxygen content to the current biological condition of the batch – often down to the absolute pain threshold of 0.4% O₂.

Facts and figures from practice

• Storage period: While apples become soft after about 2 to 3 months in normal cold storage, they remain crisp and saleable for up to 12 months in CA storage.
• Temperature: Depending on the type of fruit, the ideal cooling temperature in CA halls is usually just above freezing point at 1 °C to 3 °C.
• Oxygen reduction: From a natural 21% to up to 0.4% (with DCA procedures).
• Use of space: CA halls are usually planned as block warehouses or with special drive-in shelves in order to fill the room volume (and thus the expensive air volume) with goods to the maximum.

Frequently Asked Questions (FAQ) about CA Storage

Question: Can you simply convert a normal cold store into a CA warehouse?

Answer: Subsequent conversion is extremely costly and often unprofitable. A standard cold store is thermally insulated, but never gas-tight. The subsequent sealing of all joints, ceiling connections and the floor as well as the installation of special doors usually devour so much capital that a new building is more economical.

Question: Is it dangerous for logistics workers to enter a CA warehouse?

Answer: Yes, there is an absolute danger to life! With an oxygen content of 1 to 3%, a person loses consciousness within seconds. Under no circumstances may a CA warehouse be entered during operation without heavy breathing apparatus. Before the goods are regularly retrieved, the hall must be flushed with fresh air for several hours or days and the oxygen content measured.

Question: What goods are typically stored in the CA warehouse?

Answer: The undisputed leader in CA logistics is the apple, closely followed by pears and kiwis. Cabbage varieties, onions and, increasingly, soft fruit also benefit from the controlled atmosphere. For meat, dairy products or dry industrial goods, however, this technology is completely irrelevant.

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