Controlled Atmosphere

Controlled Atmosphere (CA) storage has been around for decades and is an affordable long-term storage solution for fresh produce. So, what is the difference between CA and DCA?

CA storage works with recognised safe O2 and CO2 regimes created by research stations to cover all sorts of growing anomalies in most global climates.

Dynamic Controlled Atmosphere (DCA) storage monitors the health of the fruit during the storage period, instead of a set regime the oxygen is reduced until the Low Oxygen Limit (LOL) is reached and then increased to a safe storage level. This LOL can vary annually depending on both climate and growing conditions.

General Information

The first large scale DCA installation was completed in the UK in 2013, by UKCA Ltd in conjunction with the Italian manufacturer Isolcell. The system uses sensors called F.I.R.M. (Fluorescence Interactive Response Monitor) to dynamically control the atmosphere allowing the storage of fresh produce at its lowest respiration rate.

The optimum level will vary considerably according to a variety of factors, including:

  • The Cultivar
  • Growing conditions before harvest
  • The state of maturity of the fruit at harvest
  • The temperature at which fruit is stored

Guidance concerning recommended “safe” levels will be provided to achieve the optimum conditions. In doing so, the storage life of the crop can be extended significantly. Additional benefits have identified that post harvest chemicals such as 1-MCP are no longer essential to maintain the quality of produce. DCA provides this security whilst also protecting against storage disorders such as superficial scald and internal browning.

Commercially, DCA is achieved using three techniques. The easiest, safest and most proven way is using Chlorophyll Fluorescence sensor, the alternative options are detecting the Respiration Quotient or the Fermentation Quotient.

UKCA are the sole suppliers of Isolcells DCA system. If you wish to discuss the viability of Dynamic Control, please contact us for an initial discussion and toarrange a site visit.

Why choose DCA storage?

With the increasing levels of Top Fruit grown in the UK the market is difficult to predict, with CA storage you may be limited to sell within a certain timescale. With DCA the increased reduction in respiration allows the storage of produce to go that bit further still, with improved pressures, great colour and reduced rots. Post-Harvest chemicals could also become a thing of the past as the reduction in Ethylene is also drastically reduced.

2013 saw the first installation of the world leading Isolcell DCA system in the UK and to 2020 UKCA have installed this system on well over 100 DCA stores throughout the UK.

DCA enables the Grower to create the ideal conditions for the medium-long term storage for most kinds of fruit and some vegetables. DCA allows the lowering of O2 levels in storage rooms to between 0.4%-0,7% (for apples) without the risk of hypoxia and correlated physiological disorders. During the storage period, using the Isolcell software “Isostore” it is possible to set and adapt the values of gases in a dynamic manner; based on the maturity, annual climatic variations, different origins and varying respiratory rhythms of the monitored fruit.

This technology uses fluorescence detection sensors to dynamically control the atmosphere and enables the storage of fruit at its lowest respiration rate. These sensors called Fluorescence Interactive Response Monitor (FIRM) measures the amount of light emitted by the fruit’s peel in the form of fluorescence. This enables us to exactly pinpoint the Anaerobic Compensation Point (ACP), an essential parameter in determining the minimum level of O2 to be maintained in the room during storage. The use of these sensors ensures the quick and precise determination of the ACP both online and in real time, making the use of ISOSTORE® technology both very easy and safe.

DCA - Chlorophyll Fluorescence

UKCA Ltd supply Isolcells DCA system due to the vast experience and continual global scientific research being carried out on this technology.

Basics off Chlorophyll Fluorescence principle involves light entering the plant and being absorbed by the Chloroplast. Most of the light is used in the process of photochemistry to create sugar. A small amount is released in a non-photochemical process as heat with some re-emitted as fluoresced (redlight) from the plant at a longer wavelength.

Commercially DCA is achieved using three techniques. The easiest, safest and most proven way is using Chlorophyll Fluorescence sensor, the alternative options are detecting the Respiration Quotient or the Fermentation Quotient.

To achieve successful DCA storage levels, the CA room and control equipment must be completely airtight to achieve and maintain <0.5% Oxygen.

CO2 Adsorbers

Despite being in a “dormant” state as a result of being cold and deprived of Oxygen, the fruit will continue to breathe (albeit at a reduced rate) and will continue to produce Carbon Dioxide (CO2). Allowed to build up unchecked, high concentrations of CO2 will cause damage to the fruit. It is therefore essential to monitor levels, and to take action to remove excess levels of CO2 as they occur.

The CO2 Adsorber (or scrubber) draws air from the store and filters out CO2 before pumping it back into the store. By circulating the air in this way, the air returned to the store maintains the important low oxygen conditions.

The Adsorber works by passing the air through a bed of activated carbon, which attracts and holds the CO2 molecules. Periodically, the machine flushes out the carbon bed by pumping fresh air through it in a reverse direction and venting to the outside before the next cycle takes place.

Generally, one Adsorber will be connected to a number of stores, treating each one in rotation via a series of valves. The operation of the machine is controlled by an internal or external analyser, which samples air regularly from each store.

Nitrogen Generators

Around 78% of the air that we breathe is made up of Nitrogen, so there is no need to make any more. What this machine does is to filter out the Oxygen from the atmosphere, along with CO2, small amounts of other gases and water vapour, to create a supply of virtually pure Nitrogen.

Using an injection system this is then pumped into the store, gradually displacing the normal air until the desired level is reached. Air from the store is regularly analysed to ensure that the atmosphere is maintained within set parameters.

Recirculation (VSA) systems are also available which take air from the store, remove the Oxygen and return to the store, thus providing a potentially more efficient reduction in store Oxygen levels.

Ethylene Scrubbers

Prevent Premature Ripening

Ethylene gas is a major plant hormone that influences diverse processes in plant growth, development and stress responses throughout the plant life cycle. Responses to ethylene, such as fruit ripening, are significant to agriculture. The core molecular elements of the ethylene-signalling pathway have been uncovered, revealing a unique pathway that is negatively regulated. Practical applications of this knowledge can lead to substantial improvements in agriculture.

By removing ethylene from the storage atmosphere, we can prevent the process of premature ripening. With all our Ethylene systems a very important benefit is the destruction of airborne bacteria, reducing mould and rotting on the surface of fruits and vegetables.


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