Dehumidification – the best solution for storing food

An Industry Insight by Christine Modla, Munters

Most foodstuff’s deteriorate when exposed to high humidity, however most materials are preserved and unaffected if humidity levels fall below 50% RH. For more than 60 years, Munters have provided solutions for safe and energy efficient storage ensuring reliable protection using desiccant dehumidification.

Desiccant Dehumidification versus heating
Heating is a common method for trying to control the humidity in stores. The relative humidity in a heated store will often fluctuate between 20-70% RH (relative humidity), exposing goods to humidity levels critical to quality and shelf life. This method can be both ineffective and costly as the energy cost for heating a store will typically be twice the cost compared to desiccant dehumidification. Keeping in mind that stored materials in a heated store will often not even be efficiently protected, heating ends up being a costly, ineffective method.

In a desiccant dehumidified store the relative humidity can be controlled and constant throughout the year – completely independent of outdoor variations, thus ensuring the stored materials keep their high quality, meaning less waste/loss and a constant and protective environment.

Maintain high quality with energy efficient dry air
All foods have their “comfort zones” securing a high quality and a longer shelf life. When exposed to too high relative humidity, food products will absorb the water in the ambient air or suffer due to condensation related problems.

Mould, mildew, insects (70%)
At humidity levels above 70%RH mould, mildew and fungus appears as the conditions are optimized for propogation affecting raw materials, food, seeds, grain etc.

Softening of packaging (55%)
Above 55%RH cardboard packaging absorbs moisture and starts to soften resulting in collapsing boxes.

Bacterial growth (40%)
Storing food or raw materials leads to high hygienic demands. Most manufacturers require humidity levels below 40%RH to avoid growth of bacteria

Most food stuffs are preserved and unaffected at humidity levels below 50% RH. For reliable protection, irrespective of external weather conditions, dry air produced by a desiccant dehumidifier is the best storage solution.

Energy efficient storage
With desiccant dehumidification air is blown though the rotor (drying wheel) and the humidity in the air is absorbed by the hygroscopic desiccant silica gel. The air leaves the rotor as dry air. In a separate sector, regeneration air is blown through the rotor to remove the accumulated moisture. The resulting wet air (which contains the removed moisture) is exhausted outside the production or storage area.

Further optimization developments for energy savings from Munters means desiccant dehumidifiers can now incorporate the latest patented Powerpurge rotor technology which reduces energy consumption even further.

Silos
Storing raw materials like sugar, cocoa, flour, salt etc. in silos often causes problems. Due to the fluctuations in the outdoor temperature condensation is created on the internal silo walls, creating a basis for bacterial growth. Hygroscopic materials absorbs moisture and cause the materials to lump together, creating handling difficulties and frequent need for cleaning. By keeping the relative humidity in the silo at a low and safe level, these problems are avoided.

Conveying
People who use conveying system’s are well aware of the problems of an uncontrolled conveying environment. Humidity levels are difficult to counteract as they change throughout the day, whilst the financial repercussions of taking a system off-line for cleaning and maintenance can be immense.

Conveying systems have their own requirements, not least the volume of ambient air moving around a system. As a general rule vacuum systems are easier to protect as dry air can be simply pulled through the system. Conveyors that use pressurised air, however, are slightly harder to safeguard, as the air is compressed and the air volume decreases, the moisture content of the air remains the same, causing the dewpoint to shift and increase condensation. This means that the average ambient air needs to be pre-dried before entering the compression and conveying system. Over the years Munters have gained extensive experience in calculating the different dewpoint and psychometric levels that achieve this.

Munters have a comprehensive worldwide databank of previous silo and conveying difficulties encountered, and are able to draw on this when planning new dehumidification systems. The dry air is supplied into the silo or conveying system at a moisture content level below that at which condensation forms. Not only does dry air decrease the amount of down time needed for cleaning and maintenance, it lowers running costs and capital investment, whilst increasing productivity and improving product quality.

Storage tents
When in need of a simple, inexpensive, method of storage, the giant tent building made from non-water permeable fabric is a perfect low cost solution. Using desiccant dehumidification for protecting the stored articles, the storage needs no insulation, just a proper air-tight construction. Whether storing raw materials or finished food, desiccant dehumidification ensures the optimal climate, keeping the high product quality at the lowest energy possible.

Breweries and cellars
Storing fluids like beer in tanks and wine in cellars, often leads to condensation on the outside of the tanks and bottles. Constantly wet surfaces form the perfect environment for bacterial growth and compromises HACCP regulations. By dehumidifying the tank room or cellar with a desiccant dehumidifier, the dewpoint of the air will be decreased so condensation no longer occurs. Building structures benefit from the drier climate, the need of maintenance work will be reduced and labels remain intact on bottle surfaces. In addition, the climate for employees will become more comfortable and healthy.

Chilled and cold stores
Stores containing food require strict control of not only humidity but also temperature. Many goods require storage at a humidity as low as 20% RH and a temperature of max 5°C to protect against product deterioration. When it comes to stores where doors are frequently opened, the high water content in the ambient air creates severe and dangerous problems as fog, slippery floors, ice build-up etc. By dehumidifying the air at the entrance to these stores, the source of the problem moisture ingress is eliminated as condensation no longer occurs.

While ice and frost disappears, the efficiency of chillers and evaporators is improved, leading to saving of energy. The need of defrosting will be significantly reduced, just like the need of cleaning. Both activities save costly manpower and avoid close down of storage.

Hygiene issues like the formation of mould on products and structures will be solved as bacterial growth is significantly reduced at relative humidity levels below 50%RH, providing greater fulfillment of the HACCP regulations.

Expert advice for the dimensioning of the optimal desiccant dehumidification solution today means taking advantage of supplier data programmes which incorporate climate data and calculate energy consumption based on customers information on building structure, moisture load etc to determine the most energy efficient solution. Compared to heating, the energy savings by desiccant dehumidifaction will typically amount to a 30-70% reduction.

Kraft Foods secure product quality
Already back in 1984 Marabou in Sweden, installed a desiccant dehumidifer to secure the high quality of their confectionery products in an automated chill store. After 24 years of impeccable functioning an energy audit highlighted that replacing the old dehumidifier with a new generation desiccant dehumidifier could cut the running cost by up to 32%.

Comparing different solutions, independent energy consultants found that the Munters desiccant solution showed the most energy efficient solution. The latest desiccant dehumidifier is now installed and keeps the condition in the 50,000m3 chilled store strictly at +5°C/50%RH all around the year – totally independent of outdoor fluctuations in temperature and humidity.

By controlling the humidity Kraft Foods experience:
•    Prevention of condensation
•    No mould growth
•    No chocolate blooming
•    Packagaing protected against softening

Jonny Hagenbjörk, responsible for constructions and energy at Krafts chocolate factory for Marabou in Sweden: “To our big satisfaction Munters took care of all details, from the difficult cut-up and removal of the old unit till completing all ductings and power installations. That made life a lot easier for us to communicate only with one supplier. We now look forward to take advantages of the benefits of the new MCD dehumidifier and feel confident that our products will be perfectly preserved, just as the dehumidifier helps us meet hygienic demands, such as the HACCP regulations”.

Food makers face a battle to prevent costly quality, hygiene and wastage issues arising during storage. Controlling high humidity in the store as part of the HACCP assessment can increase product safety, shelf life and provide greater security. Munters has offices in 30 countries and when it comes to desiccant dehumidification technology are the global market leader. Munters is concerned with air conditioning using green air treatment systems, for further information contact your local office at www.munters.com, email DHEurope@munters.co.uk or telephone Tel: +44 (0)1480 432243.