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PSI Bulletin: October 2023

No. 10/23 SPECIAL OPEN EDITION: please go to to sign up as a Synopsis subscriber. Most of our bulletins are fully accessible only to our subscribers.

Welcome to our October open edition of Synopsis, PSI's update of the latest news and technical information on potato storage.

By now, the world of storage will be firmly back on your radar in one way or another. Some growers have made good progress with harvest and may even have loaded all their stores. Others will have been struggling to cope with wet weather and many will be halfway between those extremes. The forecast going forward is looking increasingly damp so we are focusing again in our Best Practice slot at dealing with wet crop. Pull down is also a key element of management right now and I know several managers are already looking at in-store sprout control as some of the livelier varieties start to open their eyes. Our Technical Insight feature this month has a case study on a storage refit project that shows there are solutions out there for bringing older buildings up to speed at times when there is little justification for many in spending £400/tonne on a new store.

Dry rot (initially suspected as tuber blight) in cv Electra

Recent weeks have seen some hugely variable weather conditions with a distinct north /south split. And that variability is compounded by localised differences in the way crops have grown across the season. Managing diseases and defects remains important with large tubers quite commonplace, with the attendant problems of splitting and hollow heart. There also continue to be reports of dry rot (left), blackleg and tuber blight and the continuing mild and very wet weather will probably only make these worse.

For assistance on disease ID, please go to the AHDB archive or speak to Adrian on 07970 072260.


Industry initiatives

As mentioned in last month's Synopsis, PSI has become involved in a couple of major industry activities over the last few weeks, about which there is more in this bulletin.

The first is a strategic potato storage initiative involving GB Potatoes, SDF Agriculture and PSI working together with a number of partners on two stores at Winters Lane Storage and S&S Pugh. Some small collaborative trials are being undertaken on the two sites we have earmarked and we are grateful to our hosts and partner organisations for their help in getting this off the ground.

Adrian Cunnington loading respiration trials at the WLS SPoT store with Simon Faulkner of SDF Agriculture, using the CHaP/Greenwich University P-Pod system

The project will include a storage open day with exhibition space for partners in May 2024. Very provisionally we hope to be able to tell you more at our first workshop meeting for the project that we are planning to hold on Tuesday 5th December in the S. Lincs/Wisbech area. Please save the date and further information will be made available as soon as possible. In the meantime, if you are a commercial supplier involved in storage and would like to learn more about the initiative, please email or call 07970 072260.

Secondly, Adrian Cunnington at PSI has been asked by a group of industry stakeholders to be the independent chair of a new cross-industry group to be known as the CIPC Residues Monitoring Group. This follows the announcement by CRD of a new temporary Maximum Residue Level for CIPC [contamination] in potatoes, to be set at 0.35 mg/kg. This is especially relevant to any stores previously treated with CIPC as the industry is being asked to supply residue data to the authorities on CIPC levels from 125 such stores from this season's crop. We therefore need the assistance of the many different supply chains in doing this. Failure to supply the data would result in removal of the tMRL and the CIPC threshold being dropped to the limit of quantification (0.01 mg/kg). On the basis of current data, this would render previously treated stores unusable going forward. There is more detail below.

Harrogate preparation

PSI has been busy preparing for next month's trip to exhibit at the BP2023 event in Harrogate. The show is again being held at the Great Yorkshire Showground site on 22 & 23 November. Click here to register in advance for free entry. We hope to see you there!

You can find us on Stand 135 in Hall 1. Do come and have a chat! We will have information available about our various services and some new announcements about future activities.

A reminder too that we will be a contributor to the seminar programme which will return at this year's BP2023 event, after a Covid-enforced absence last time we were there.

The storage seminar is on Day 1 at 12.45pm. PSI's Adrian Cunnington will be speaking on energy efficient management of stores and will also chair the session on optimising use of sprout suppressants, featuring an expert panel of Jeff Beever (McCain Foods), Gary Collins (Pepsico) and Richard Baines (Lamb Weston Meijer).

BEST PRACTICE for October/November

Drying remains a priority for all crops going into store

Normally, crops are best loaded into stores that are, ideally, at temperatures just a little cooler than the crop itself.

The priority as they go in, is always to get them dry as quickly as possible and, following unprecedented rainfall (again) in mid-October, this will become ever more important as we move deeper into the maincrop lifting season, assuming the weather relents enough.

In an ideal world, we would have wanted all crops into store by now but many growers don't have that luxury and so there may be a need to adapt loading processes to rescue marginal crops and this means ensuring that effective drying takes place.

Always remember that rained-on or fully waterlogged potatoes (where the lenticels have inverted) do not store so don't mix any affected crop with good potatoes. Store it in short-term facilities so it can be moved on quickly after harvest.

For any crops coming out muddy or from very wet soils, ventilate as soon as possible to remove any excess moisture. This means getting air into contact with the crop. The additional measure that is likely to now be needed for a very wet phase of harvest is to 'force dry' crops. In bulk, that is fairly straightforward (keep stacks at a modest height and close off any unused ducts) but, with boxes, it could be necessary to put the boxes on a letterbox drying wall (if available) or to rig up a temporary fan arrangement to force air through boxes using foam bungs to block the pallet slots.

Here's some further tips we included in last month's bulletin, repeated for reference:

  • Remember that air takes the path of least resistance, so blowing it randomly around a small stack of boxes in the middle of a big shed is not going to work well.

  • Ideally, stack the boxes across the shed to ensure air has to pass through the pallet slots.

  • If you need to stack differently try to isolate the air to a part of the store to maximise flow through the crop. Keep the air moving through the potatoes until any free/surface moisture is removed.

  • Note too that, wherever we are evaporating moisture to dry crop, it will also result in some degree of cooling due to the latent heat of evaporation.

Once crops are dried, make sure they are adequately cured before reducing the temperature. The later harvest is, the greater the risk of poorer curing, especially if field temperatures drop below 7°C. Cut a few tubers and leave them on the surface of a box or stack to monitor the effectiveness of curing over time.

Bacterial soft rot is a major risk in wet crops as the anaerobic (airless) conditions encourage development. To keep soft rot development at bay, the key is to ensure crops are kept (a) dry as described above and (b) cool. In severe cases, it may be necessary to lower set points by as much as 2 or 3°C below normal to reduce risk adequately. Any crops with over 1% soft rot should not be considered candidates for long term storage.

If, as we move through the storage season, you'd like to discuss how best to handle a particular scenario or get some advice on how your store management strategy can be strengthened, please call Adrian Cunnington at PSI on 07970 072260.


CASE STUDY: Don't give up on those older buildings! Energy efficient conversions and upgrades are still possible...

With the industry under the cosh for much of the post-Covid period, it is perhaps not surprising that growers have been forced into a defensive position when it comes to potato storage in recent seasons.

There are a few green shoots of recovery coming to light but, with new storage costs sky-rocketing to north of £400 per tonne. the focus for growers for now seems to be very clearly on directing any improvements towards what already exists rather than starting from the ground up.

An example of this approach provides a case study we visited recently. It is a store upgrade carried out this summer at Drayton Farms at Little Plumstead on the outskirts of Norwich, Norfolk by North Walsham-based suppliers Crop Systems Ltd. A pair of rather tired 1980s-built stores became the subject of an upgrade proposal with the objective of converting them to provide around 1500 tonnes of high quality, pre-pack storage.

The buildings themselves were metal-clad portal frame units with a modest amount of spray-foam insulation that was cosmetically damaged. Crop Systems proposal was to remove a central, non-structural dividing wall and a couple of existing fridges which were well past their use-by date. The installation would repair and renovate the spray-foam to provide around 85 - 90mm of good quality insulation across the newly-created, larger store. The doors were also a weak point in the store's overall integrity, as is so often the case, so these were to be replaced with new Hormann up-and-over units with 40mm insulation.

Box stacking in older buildings can often be a challenge so this required some flexibility of thought but Drayton Farms gave the project the go-ahead based around the promise of close store control from the new SmartStor® controller and a state-of-the-art cooling and ventilation system designed and installed by Crop Systems' directors, Ray Andrews and Richard Cook (right).

Boxes are stacked in a reworked but largely conventional format away from a full-width, but open-fronted, plenum chamber which allows the store to flex around a couple of differing box sizes on the production unit.

The store has an ambient, inverter-controlled drying system with full dew-point control to prevent condensation. The airflow is rated at ~0.03 m3/s/t (65 cfm/t) with the fans running flat out and that is at a nominal 150 Pa pressure. The store pairs the 'free cooling' option with a 90kW, glycol-based 4-compressor refrigeration unit which is fully speed-controlled. It is linked to a large, 6.4 metre wide refrigeration coil providing a big interface for efficient cooling to minimise weight loss. The indirect system uses around 600 litres of glycol (running at -2.6 to -3°C) but just a 16kg charge of refrigerant.

When PSI visited, the store had completed the drying/curing phase, when it was held at a target temperature of 8°C, and was in the process of pulling down to holding temperature. Pull-down rate was close to 1°C/day even with the system running at just 80% on the inverter, which offers a 50% reduction in power consumption compared with running at 'full chat'.

Air distribution is not 'textbook' due to the low roof but it works well. The crop is Elfe destined for Albert Bartlett.

Large fridge coil dominates the plenum

According to Mr Andrews, the modern design of the fully configurable system can reduce running costs by as much as 30%.

This is due to the combination of key design characteristics such as the high airflow, low back pressure and large fridge coil coupled with the ability to speed control all the key components.

A quick calculation using the consumption data instantly available on the SmartStor® control system showed drying and pull-down costs to be approximately £2.65 per tonne since loading on 28 September (to 18 Oct at 32p/kWh).

And, as far as the conversion costs go, Crop Systems estimate the cost of bringing this old store back to life at about £140/t.

SmartStor® controller includes dew-point control to prevent ventilation during times of high condensation risk (shown in red)

That figure includes the all-important control unit which provides real-time information and data not only for the store conditions but also power use.


The CIPC Residues Monitoring Group (CRMG) is a cross-industry body which has been set up by the UK potato industry. The Group has been established to set up a mechanism to satisfy the data submission requirement of Health & Safety Executive’s Chemical Regulation Division (CRD) for measurement of chlorpropham (CIPC) residues in potatoes held in potato stores previously treated with CIPC.

It is incumbent on everyone in the industry to ensure that data CRD has requested are provided so that potato stores previously treated with CIPC can continue to be used. If the data are not supplied, all stores with a CIPC treatment history could be taken out of use.

CMRG has already been given pan-industry support from the following organisations who have offered representatives to input to the Group:

GB Potatoes, UK Potato Processors Association, Fresh Potato Suppliers Association, National Farmers Union, National Association of Agricultural Contractors, Certis Belchim, UPL, CSBackhouse, Isle of Ely Potatoes, Potato Storage Insight and SA Consulting.

Now, the Group is seeking the co-operation of growers and suppliers from all production sectors to provide residue data from compliance sampling for over 120 potato stores annually to meet the CRD data requirement.

If you are able to supply us with CIPC data from crops held in your stores, please email The Group will act in the interests of the whole of the UK potato industry to ensure that the data submitted meets the quantitative and qualitative standards expected by CRD with the aim of allowing CRD to maintain the new temporary Maximum Residue Level (tMRL) for CIPC through its annual review process for an initial period of five years proposed by CRD.



Farmers Weekly ran an article by Adam Clarke earlier this month along similar lines to the one our subscribers received in our last bulletin in September. It was entitled 'Should you use DMN in potato stores this season?' Follow this link if you missed it.


PSI was disappointed to hear within the last few weeks that JD Cooling Systems, a significant player in the refrigeration market for potato storage over the last couple of decades, entered administration on 17 August 2023. The specialist refrigeration publication Cooling Post reported:

'The King’s-Lynn-based business was placed into the hands of administrators McTear Williams & Wood, putting the future of 150 staff at risk.'

There is, however, a suggestion in the article that there may still be a future for the maintenance division, as it continues:

'The service and maintenance business of JD Cooling Systems was acquired by its directors in a pre-packaged deal for £162,116, the administrator’s report reveals .

In a note announcing the sale on the administrator’s website, Jo Watts, joint administrator and associate director at McTear Williams & Wood, said “Every case is different but in this instance we were able to save over 40 jobs and see the servicing and maintenance part of the business continue with its many loyal customers, which in today’s economic climate is a very good outcome.”

The administrator has so far not revealed the identity of the purchaser of the service and maintenance business, nor the purchase price, but has indicated that there will be a dividend for unsecured creditors. Following a number of successful years, JD Cooling made a loss of £939,581 in the year to May 31, 2022, after seeing turnover drop from nearly £30m to £16.5m.'


Potato events in the coming weeks and months include:


Sun 12 - Sat 18 AGRITECHNICA, Hannover, Germany

World-leading trade fair for agricultural machinery

Wed 22/Thu 23 BP2023, Harrogate, Yorkshire, UK

Biennial industry-wide exhibition and knowledge transfer opportunity for everything to do with potatoes. Seminar programme includes storage. Registration now open.

Wed 29/Thu 30 CROP TEC, NAEC, Stoneleigh, Coventry, UK

Two day technical arable farming exhibition


Tue 05 GB Potatoes/SDF Agriculture/PSI Strategic Potato Storage meeting

Save the date; more details to follow. See above.

Tue 12 - Wed 13 CUPGRA 34th Annual Conference, Cambridge. Save the date!

2 day ticket: CUPGRA members £138, non-members £281;

1 day ticket: members £72, non-members £165

2024 International Potato Events

10-11 Jan POTATO EXPO, Austin, Texas, USA


23-26 Jun WORLD POTATO CONGRESS, Adelaide, Australia

7-12 Jul EAPR 22nd TRIENNIAL CONFERENCE, Oslo, Norway

24-26 Nov INTERPOM '24 Kortrijk, Belgium

Remember you, or a colleague, can subscribe to Synopsis at any time by going to and clicking on SUBSCRIBE. We can also now take payments by credit card. Call Adrian on 01406 364795 or 07970 072260 if you have any questions.

Subscriptions: we issue invoices as individual subscribers reach the anniversary of their payment. A full year's subs is great value at just £9/month (£108 + VAT per annum), so please renew promptly. Unpaid subscriptions will be closed within 8 weeks of invoice issue. Thank you.

Synopsis is published by Potato Storage Insight Ltd., 45 Main Street, Gedney Dyke, Spalding, PE12 0AJ. UK.

© Potato Storage Insight Ltd. 2023


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