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Are your old potatoes getting too sweet?

Publication Date: 
15 May 2019
Author/Contact :
Laura Bouvet

Preventing ‘sweetening’ or the accumulation of reducing tubers in tubers is crucial to maintaining processing quality. While this is normally achieved by storing tubers at warmer temperatures, usually 6-12 °C depending on the variety, this solution is not effective when tubers start to get old or senesce. As the tubers start to age and break down physiologically, the process of reducing sugar accumulation becomes irreversible and ‘reconditioning’ tubers at warmer temperatures will worsen the process. Store managers should be vigilant at this time of year and in particular this year, as the high temperatures experienced in the field in the 2018 season have fast-tracked the physiological ageing of tubers, potentially leaving them more prone to senescent sweetening in stores.

Although it is difficult to predict the onset of this physiological process, regular fry tests - every one to two weeks - will enable you to detect any adverse change in fry colour. If darkening is observed, contact your supplier and take prompt action to move the crop before senescent sweetening becomes a more serious issue. For best results, sampling should be made from the same position in store.

Two recent AHDB-funded PhD projects (11140014 and 11140024) have shed some light on the biochemistry underlying senescent sweetening and associated processes. An increase in tuber respiration has been found to be associated with increased senescent sweetening. Enzymes in the carbohydrate metabolism pathway and their corresponding genes have been identified as promising targets for the development of senescent sweetening indicators.

For further information and advice on senescent sweetening, get in touch with Sutton Bridge storage specialists by calling the free Storage Advice Line on 0800 02 82 111 or e-mail A research review is also available to read.

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