ULO System

The ideal oxygen level for storing pears must be between 1 and 3%; for some varieties of apple, however, it must be lower than 1%. Storage under such O2 conditions is referred to as Ultra Low Oxygen (ULO) storage. ULO storage takes place in gas-tight cells and is used for the long-term storage of apples, pears, blue berries and kiwis.

Ultra Low Oxygen (ULO)

What do you need for ULO storage?

O2-scrubbers
With a CA scrubber (also known as a nitrogen generator or a separator), the fruit can be quickly brought under CA/ULO conditions once the space has been filled or after a connecting door, for example, has been opened.
CO2-scrubbers
CO2-scrubbers are used to manage the CO2 levels in the cool cell. Air from the storage area is removed by the scrubber, and the CO2 purified air is then fed back in.
Control systems
A control system measures and registers O2 and CO2 and operates the CO2 and O2 scrubbers. In addition, the same control system can regulate cooling (switching on/off, defrosting, machine room regulation), carry out ethylene measurements and operate the ethylene converter.
Ethylene converters Fruit varieties that are sensitive to ethylene (under CA conditions), such as kiwis, require an ethylene converter. The ethylene converter from the cool cells using catalytic combustion; ethylene can thus be maintained at any required level.
Humidification
Fruit that is stored in a CA/ULO cell always loses moisture. This moisture loss reduces if the RH levels (relative humidity) are kept above 90%. Cooling takes water out of the atmosphere, thus limiting the storage period and quality. A humidification system means that relative humidity can be kept up to scratch.
Gas-tight cool cells
A gas-tight cool cell is made up of gas-tight insulation panels. A gas-tight environment is created using mould-resistant kit and fleece seals. A CA cool cell is closed with a gas-tight door and a window is fitted into the door, the corridor or the roof of the cool cell. This enables samples to be taken and the fruit to be viewed.
Accessories
Finally, the CA cool cell is also fitted with a couple of accessories that are vital.
- a flexible buffer (also called a 'lung') absorbs pressure differences in the cool cell without oxygen streaming into the cell.
- under and over pressure valves ensure that larger pressure differences (which cannot be absorbed by the air buffer) are evened out so that the cool cell is not damaged.

The floor and the door are important points when making sure the cell is leak-proof!