Science into Practice: Optimum curing regimes for fresh onions

As part of a much wider HDC project, the effects of curing regimes on onion quality was investigated.

Innovatively, project FV 308 enlisted the expertise and experience of growers to assess the treatments with some interesting results.

The aim was to establish the optimum curing regime with the lowest energy input that would be capable of providing sufficient control of post-harvest neck rot. Three varieties of bulbs (Red Baron, Sherpa and Wellington) from two sites were harvested into bulk bins and dried/cured at three temperatures: 20 degsC, 24 degsC and 28 degsC. The bins were then put into long term storage.

Prior to a grower open day in May, any weight loss during storage and the proportion of rots and rejects was assessed. The samples were displayed blind and growers were asked to estimate the likely curing temperature, based on their experience, and score the samples' overall quality.

There was very little difference between curing temperatures for any trait with no obvious difference in weight loss. There was no evidence of more neck rot at the lower curing temperatures and no difference in internal growth and subsequent sprouting was detected.

On average, growers were 50% accurate at estimating correct curing temperatures. Grower preferences seemed to favour lower temperatures as producing better bulbs.

Curing at lower temperatures of 20 degsC or 24 degsC rather than 28 degsC had only marginal effects on appearance and did not affect quality traits such as weight, pungency, disease incidence or sprout growth, so growers could spend less on energy inputs during curing and still deliver quality.



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