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Storage Bulletin - September 2013

Publication Date: 
18 September 2013

Stores gearing up to load in earnest

Loading is underway in many stores around the country and will be gearing up significantly over the next couple of weeks. Recent rain will hopefully have eased the risk of bruising, but warm growing conditions have tended to encourage sprout growth in short-dormant varieties; these will need cooling quickly or treating with CIPC early (see below) to maximise control.

Achieving skin set may be difficult in some varieties but remains important if disease is to be kept at bay. There are several reports of bacterial rot in the field and the risk from fungal infection will be high if temperatures return to more seasonal levels, close to 15°C. Disease risk from fungi such as pink rot could be a threat in crops grown in fields which were waterlogged last year. 

To minimise risk, always ventilate crops when they first come in store to remove field heat and aerate the stack to aid curing. Don’t overfill boxes as this constrains airflow at the most critical time for the crop. Also make sure warmer air is not blown on to cooler potatoes if the difference in temperature is more than a couple of degrees, as this is likely to result in condensation.

Processing growers will probably want to leave crops to grow out to maximise yield but do balance this with the need to get crops into store in best condition, especially if long term contracts need to be met. Whatever market is being supplied, there will be a need to revise sprout suppression strategies for many in the light of the new advice on CIPC labels for this autumn’s treatments. The label recommendations are summarised on the next page.                                                      

  • box A new Store Manager’s Diary themed on the Be CIPC Compliant campaign will be available shortly: order a free copy for each of your CIPC-treated stores by calling 0800 02 82 111.


Be CIPC Compliant – are you?

As changes in the way CIPC can be used are already in place for 2013, it is important to be in touch with your contractor now. The Advisory Committee on Pesticides undertakes its full Review of CIPC later this month. Keep up to date with any further developments by going to the Potato Industry CIPC Stewardship Group’s ‘Be CIPC Compliant’ website at                               

  • New CIPC label recommendations for 2013/14:
    First treatment recommended within 3 weeks after harvest (or at the earliest occasion thereafter) even in the absence of signs of breaking dormancy.
  • TREATMENTS IN COLD STORES (holding temperature 5oC or below)
    Only one application of CIPC up to the maximum individual dose per season recommended. The application should be made before the temperature is reduced below 7°C. Recirculate store air for at least 6 hours without cooling prior to application.
    Positive ventilation is recommended in all store types.

Are you getting value from your store?

Continuing this theme from the last bulletin, against a background of rising costs, it is worth thinking a little harder about the efficiency of your storage. Maximising returns can be significantly improved by controlling costs.

The key to this consideration is having access to accurate information. Best practice recommendations start with the installation of a dedicated electricity sub-meter on each store. AHDB Potatoes-funded R&D work carried out by Sutton Bridge CSR and Farm Energy has been assessing energy use and has shown as much as a 3-fold difference in running costs across stores within the same sector. To ensure your business is competitive, consider some of these areas that the project has investigated:

Air leakage

For optimal control and cost-effectiveness, storage buildings need to be isolated from the effects of the external environment. If they are not, there is a cost to bear in two ways: first the effect of any loss of control on crop quality (e.g. from condensation) and, secondly, the cost of energy to restore the store to the desired condition, usually through ventilation and/or mechanical cooling.

The project has assessed air leakage in commercial stores by lightly pressurising the building and then monitoring the fall in pressure as a result of the leaks present. This assessment can then be integrated into a single figure equivalent to the area of leakage present. Stores assessed had leakage equivalents from just below 1m2 up to a concerning 5.5m2 which would clearly be difficult to control on a day when the store comes under significant wind pressure (both positive on the windward and negative [suction] on the leeward side).

A basic leakage assessment can be undertaken by entering a closed store with the lights off to identify any primary leaks which should then be sealed with foam or by fitting rubber seals/brushes.   

Fridge efficiency

Where a fridge is used in a potato store there are a number of heat transfer processes to be gone through to extract the heat from the store.

  1. Heat is first given up to the air around the potato and this then has to be effectively transferred by ventilation to the fridge coil.
  2. At the coil, heat is transferred to the refrigerant as it is evaporated. It is then pumped to the condenser outside the store.
  3. At the condenser, it is important that the heat can then be effectively released to the outside air through the condenser fins to the cooler air circulated by the condenser fans.

Uniform air movement in the store is important for stage 1 to ensure even heat pick-up. At stage 2, regulated air flow over the fridge coil at a controlled temperature difference is important to balance cooling and moisture loss. Finally, at stage 3 heat needs to be effectively dissipated or it will return to the store and limit cooling further.

A measure of how well a fridge works is its Coefficient of Performance (CoP), which is a measure of kW of cooling achieved for each kW of energy input. Typically a fridge’s CoP will be around 3 (i.e. 3kW cooling per kW of electricity) but, in the project, figures were measured ranging from 1.6 to 4.0, showing a 250% variation from poorest to best.

Practical measures to improve fridge performance would include closing off potential short circuits for air in the store; regular servicing of fridges including maximising the refrigerant charge; cleaning of evaporator and condenser coils; removal of debris and obstructions around condensers which might impede airflow. It is also possible to enhance condenser performance by upgrading to continuously ventilating, speed-controlled fans rather than the pressure-switch controlled systems, which tend to run just 2 out of 4 fans for much of the time. The full project report will be available at shortly.


Dates for your diary:
27/28 November, BP 2013, Harrogate, Yorkshire
9 January 2014, Winter Forum (East), Sutton Bridge Crop Storage Research
22/23 January, AATP Advanced Potato Storage Course, SBCSR
23 January, Winter Forum (West), Harper Adams, Shropshire
13 February, AHDB Potatoes Storage 2020 Conference, Peterborough Arena
27 February, AHDB Potatoes Storage Meeting, Angus
5/6 March, Potato Store Managers’ Course, venue to be confirmed
For further details, please see

AHDB Potatoes Storage Advice Line

Call free for help on any aspect of potato storage on 0800 02 82 111

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