ULO (Ultra Low Oxygen) Storage in Warehouse Logistics

ULO (Ultra Low Oxygen) Storage in Logistics

If you want to store fresh products such as apples, pears or kiwis in immaculate quality for many months, conventional cold storage systems quickly reach their physical limits. The modern supply chain's answer to this challenge is ULO storage (Ultra Low Oxygen). But what looks like "fresh from the tree" to the end consumer in the supermarket is the result of highly complex technology. In the background, this process requires specialized logistics properties, massive capital investment (CAPEX) and the highest operational expertise in contract logistics. This guide examines the topic holistically for real estate developers, logistics service providers and supply chain managers.

What is ULO Bearing? (Definition & How It Works)

The abbreviation ULO stands for Ultra Low Oxygen . It is the technological development of the well-known CA (Controlled Atmosphere) storage. In this specialized warehouse logistics process, not only is temperature and humidity strictly regulated, but the composition of the room air is drastically changed.

While normal breathing air consists of about 21% oxygen (O₂), this proportion is artificially reduced to values of less than 1.0% (usually 0.5% to 0.9%) in an ULO warehouse. At the same time, the carbon dioxide content (CO₂) is slightly increased. This massive deprivation of oxygen almost completely stops the cellular respiration of the stored fruits. The biological clock of the products is put into a kind of artificial hibernation. Ripening processes, rot and the breakdown of vitamins are thus extremely slowed down.

The subtle difference: CA storage vs. ULO storage

The terms CA and ULO are often used synonymously in logistics practice, but this is imprecise from a technical point of view. The main difference lies in the degree of oxygen reduction and the resulting structural demands on the hall:

• CA (Controlled Atmosphere) storage: The oxygen content is reduced to about 1.0% to 3.0%. This is the standard for many fruits and vegetables.
• ULO bearing (Ultra Low Oxygen): The oxygen content is reduced to below 1.0%. This requires an even more extreme guest tightness of the logistics property and more sensitive measurement and control technology, as the tolerance limit for suffocation of the fruit is minimal.

Structural requirements for the logistics property (CAPEX)

From the perspective of real estate development, an ULO hall is the absolute premier class of refrigerated logistics. The construction requires a massive capital investment (CAPEX), as conventional insulation and construction standards are far from sufficient here.

The most important structural criterion is absolute guest tightness. If oxygen penetrates into the hall from the outside or the artificially created gas mixture escapes, the harvest of months is at risk. The walls and ceilings of the logistics property consist of highly insulating sandwich panels. All joints, corners and ceiling connections are sealed gas-tight several times (e.g. with permanently elastic special paints or films). The industrial floor is also given a special gas- and vapour-tight coating to prevent diffusion through the concrete.

Access to the hall is via heavy, hydraulically sealing ULO special doors. These are also equipped with a small viewing window (porthole) so that the goods and the instruments can be visually inspected without having to open the door. In addition, special pressure equalization valves (rubber lunges) are absolutely necessary to prevent damage to the building structure due to atmospheric air pressure fluctuations.

The technical infrastructure: More machine than hall

In order to generate the ultra-low oxygen atmosphere and keep it constant for months, highly complex plant technology is required within the logistics property:

• Nitrogen generators (N2 separators): They flush the room with nitrogen at the beginning of storage in order to actively and quickly displace oxygen from the hall.
• CO₂ adsorber (scrubber): Since fruits still breathe minimally even in the ULO dormant state and release carbon dioxide in the process, excess CO₂ must be washed out of the air regularly to avoid suffocation damage to the product ("browning" of the pulp).
• Ultrasonic humidifier: To prevent the goods from drying out, shrinking and losing sales weight during continuous cooling, the humidity is kept constant at 90 to 95%.

ULO Warehousing in Contract Logistics: Business Model & Value Added Services

For contract logistics companies, operating an ULO warehouse is a highly profitable, but also risk-prone and capital-intensive niche. The business model is strongly seasonal: the hall cells are completely filled at harvest time (e.g. in autumn), sealed and often only gradually opened for marketing months later.

The operating costs (OPEX) are enormous. In addition to the high energy costs for permanent cooling, the operation of the gas generators, the maintenance of the scrubbers and the constant sensor-based IT monitoring of the parameters have a massive impact. Successful logistics service providers differentiate themselves here through valuable value-added services (VAS). Since an ULO cell has to be emptied quickly after opening, contract logistics specialists then take over quality control, final sorting (calibration), packaging into supermarket-friendly packaging and just-in-time distribution (outbound logistics) in the food retail trade (food retailing).

Facts and figures from logistics practice

• Oxygen content (O₂): Reduced from a natural 21% to an extremely low 0.5% to 0.9%.
• Storage period: While apples become soft after 2 to 3 months in normal cold storage, they remain  crisp and saleable for up to 12 months in ULO storage.
• Room temperature: Depending on the type of fruit, usually just above freezing point at 1 °C to 3 °C.
• Humidity: Consistently high at 90% to 95% to stop moisture loss.
• Construction costs (CAPEX): The investment costs for an ULO hall are estimated to be 30% to 50% higher than for a conventional deep-freeze or cold storage facility.

Frequently Asked Questions (FAQ) about ULO Storage

Question: Is entering an ULO warehouse dangerous for logistics employees?

Answer: Yes, there is an absolute danger to life! If the oxygen content is below 1.0%, a person loses consciousness within seconds without warning. Under no circumstances may an ULO warehouse be entered during operation without a heavy breathing apparatus that is independent of the recirculating air. Before regular retrieval, the hall must be flushed with fresh air for many hours and the O₂ content must be meticulously measured.

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

Answer: A subsequent conversion is technically extremely complex and usually economically unprofitable. A standard cold store is thermally insulated, but never gas-tight. The subsequent sealing of all joints, ceiling connections and the porous concrete floor as well as the installation of special gas doors usually devour so much capital that a new building (built-to-suit) is much more economical.

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

Answer: The undisputed leader in ULO logistics is the apple, closely followed by pears and kiwis. Special cabbage varieties or onions also benefit from the controlled atmosphere. For meat, dairy products or dry industrial goods, this technique is completely unsuitable and irrelevant.

Question: What is DCA and how does it differ from ULO?

Answer: DCA (Dynamic Controlled Atmosphere) is the technological spearhead. While ULO works with static, extremely low O₂ values, DCA uses special sensors (e.g. via chlorophyll fluorescence) to measure the "stress level" of the stored fruit in real time. The logistics IT then dynamically adjusts the oxygen content to the current biological condition of the batch, often down to the absolute pain threshold of 0.4% O₂.

Conclusion: A niche with maximum ambition and high returns

ULO storage is much more than just cooling fruit. It is the perfect interplay of highly specialized logistics property, state-of-the-art plant technology and precise contract logistics. Investors or logistics service providers who overcome the massive hurdles in construction costs (CAPEX) and operation (OPEX) will secure lucrative long-term contracts with the agricultural and food industry in this niche and make themselves indispensable for a supply chain that is fresh all year round.

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