The pursuit of an excellent potato skin finish is vastly improved when crops are harvested early and cooled very quickly when they enter a store, according to British Potato Council (BPC) research.
“BPC funded trials showed that using a plant dessicant and harvesting a crop early saw a three-fold reduction of a skin blemish like black dot compared with a later harvest. In addition, low levels of black dot seen at harvest were maintained when store temperature was kept at 3°C,” says Dr Jeff Peters, BPC plant pathologist.
Quality sapping diseases like black dot and silver scurf, which leave unsightly blemishes on a potatoes’ surface, cost the UK industry £5 million each year through rejection by buyers.
Directly after harvest, the number one objective should be to lower the temperature of incoming potatoes as soon as possible. “The temperature of harvested potatoes can be as high as 16°C. This must be reduced to the stores’ holding temperature quickly. And unless crops are kept well ventilated and dried once in store, there is a high risk of creating the anaerobic conditions which encourage the development of bacteria that cause soft rots,” says Peters.
Even where growers and store managers have managed to carry out rapid cooling and have ventilated the crop well, they should still monitor store temperatures regularly and thoroughly.
Peters also points out that a top quality skin finish can never be achieved unless stores are cleaned and have a low risk of carry-over disease.
“Growers and store managers should leave nothing to chance when cleaning their stores. Now is the ideal opportunity to get into stores and start a thorough cleansing. For specific advice contact the Sutton Bridge storage help line,” he says.
Peters believes that each store should have quality control procedures in place to ensure crops will meet the requirements of their market’s specification. The BPC has produced practical guides packed full of information to help store managers carry out thorough quality control checks. He suggests checks should mirror the buyers’ quality assessment methods wherever possible. “That way growers will supply potatoes of the correct specification and can negotiate borderline crops with their buyer,” he says.
Potato growers selling crops for processing need a regular, consistent in-store sampling procedure that matches the quality checks carried out by their buyers. To help, the BPC is urging growers and store managers to obtain copies of their quality control guides and fry colour charts. BPC technologist Adrian Briddon says: “Get into the habit of making regular checks, taking potatoes from all parts of the store and frying samples to assess for fry colours.”
Most rejections from processors are as a result of fry colour problems and this costs UK growers around £400,000 each year. Briddon explains: “Quality control is an investment. It provides immediate feedback on changes in the stored crop and I encourage growers and store managers to use their buyers’ quality control reports to audit their own procedures.”
BPC research looking at how to achieve the right fry colours for crisps and chips at BPC’s Sutton Bridge Experimental Unit shows that switching store fans on earlier after applying Chlorpropham (CIPC) will maintain sprout control and improve the quality of processing potatoes in long term storage. Around half of the UK’s stored crop is treated with CIPC to reduce sprouting.
Work demonstrates that CIPC itself is not to blame, rather the fuel used to generate the CIPC fog. This introduces ethylene to a store and also carbon dioxide, which does adversely affect the fry colour of processing potatoes.
To ventilate effectively and safely may require simple modifications to some stores, Briddon says: “For health and safety reasons operators are not allowed to enter a store until at least 24 hours after a CIPC application, so an inexpensive outside switch and a good touch would overcome this problem. What’s more, a viewing glass would allow the operator to see what’s happening inside the store from outside the building,” he adds.
The BPC is confident that a combination of proper quality control checks and early ventilation will result in fewer loads being rejected. However, it reminds growers that the effects of gasing on fry colour are not as dramatic as storing the crop at the wrong temperature.
STORAGE COSTS
When it comes storage costs, the BPC is challenging growers and store managers to identify all their potato storage costs before this season’s crops are harvested. BPC storage expert Adrian Cunnington, says it is imperative that businesses know the true cost of storage, why it costs that amount and where to make efficiency savings.
Building and box depreciation, electricity costs, potato weight loss, finance charges, chemical costs and equipment maintenance should all be accounted for in any calculation.
Industry needs to understand why a pre-pack crop for the fresh market costs £30 to £40 a tonne to store long term and crops going for processing fall within the £20 to £30 a tonne range.
Cunnington explains: “Businesses can use their findings to assess the options for reducing their storage costs. Carrying out a BPC Store Improvement Check would enable these to be identified. Reducing costs could be as simple as preventing air leaking into a store or changing electricity tariff.”
Growers are also encouraged to benchmark their business using updated BPC benchmark software and to talk to their supply chain about storage costs. “Whatever method you decide, I recommend action sooner rather than later and certainly well before this season’s crops enter the store,” says Cunnington.
A BPC survey of store owners earlier this year revealed that only 15 per cent identified the right cost range of their storage.
STORE CHECKS
At this time of year store owners should be devising a plan that includes key members of staff to help make a careful inspection, points BPC knowledge transfer manager, Dr Rob Clayton. “Remedies are often inexpensive like repairs to insulation or plugging leaky door casings. But these could be the difference between a crop either making the grade or failing when the store is full. It only takes a matter of hours to reduce quality and erode premiums,” he says.
And now is also an ideal time to plan an essential quality control programme, ready for when stores begin to fill. This should focus on regular and rigorous quality control checks and that means taking samples from all points in a store.
“Installing a ladder to be able to collect samples from throughout a store could make the difference between success and failure. Sampling just the lower boxes isn’t representative. Trouble could be brewing up above and may be made 10 times worse if a sprout suppressant is applied when not required,” says Clayton. “When potato stores are loaded the general rule with store management is to expect the unexpected. Check and double check. If things seem too good to be true, it is probably the case.”
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