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Storage Bulletin - May 2015

Publication Date: 
19 May 2015


As the season progresses, store managers need to be aware of senescent sweetening and ensure their crops do not succumb to this alternative type of sweetening, linked to the age of the crop. Storage of potatoes for processing is based initially on the avoidance of low temperature sweetening – which results in unacceptable fry colour from the accumulation of reducing sugars – and is ensured by holding such crops at a relatively warm storage temperature (typically 6-12°C, depending on variety and end-use). But holding crops at a warm storage temperature effectively shortens storage-life and limits the duration over which potatoes can reliably be supplied with a light fry colour. Potatoes have a finite life, and at warm temperatures, the ‘clock’ governing that life ticks faster.

It’s important for growers and store managers to monitor fry colour late in the storage season, because senescent sweetening and the resulting poor fry colour, is irreversible. Raising the store temperature, to recondition the crop, will only make matters worse. Senescent sweetening is most easily detected by repeating fry tests at about 1-2 week intervals. Use the same lot of potatoes, sampled from the same positions in store, to look for any reduction in fry quality. If fry colour deterioration is detected, speak with your processor and, if this is confirmed, make plans to unload the store. But don’t raise the storage temperature!

The causes of senescent sweetening are still quite poorly understood but the increase in sugar content occurs because of a loss of membrane integrity, with reactions at the cellular level becoming uncontrolled. A review of senescent sweetening can be found on the AHDB Potatoes website at
Senescent sweetening is the subject of on-going AHDB Potatoes research at the Natural Resources Institute, University of Greenwich:


This stage of the season is increasingly the time when crops taken from storage have a greater risk of suffering from blackheart during subsequent packaging and shelf-life. Recently completed levy-funded work at SBCSR indicates that the risk is highest in large (over 60mm) tubers from susceptible varieties (eg Maris Piper, Marfona) stored at low temperature (especially below 3½°C) and for the longest period from harvest. Over the summer, a guide to blackheart risk assessment will be produced. The trial work included development of a test protocol for assessing risk at intake, which it is planned to include in the guidance. 


A reminder that, as already announced in the farming press, AHDB is moving to a simplified family of brands for its activities across agriculture and horticulture. This will, therefore, be our last storage bulletin under the AHDB Potatoes name and Sutton Bridge Crop Storage Research will be part of AHDB Potatoes from 10th June.

ON-FARM STORAGE DAY — 24th June kindly hosted by Heal Farms, Shawbury , Shropshire, SY4 4HG

This event will include commercially-focused presentations on key storage topics. There will also be some practically-focused demonstrations and workshops to illustrate research results and the adoption of best practice, all seeking to make a difference to storage. Some major storage suppliers who have been collaborating on Sutton Bridge R&D projects have been invited to the event and there will be plenty of networking available during coffee breaks and over lunch.

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