Classifying mild onions

Onions that are mild in flavour and suitable for eating raw are to be labelled as mild under a new onion classification system.

Research by the NSW Department of Primary Industries (DPI) has demonstrated that pungency of mild onions can be reliably assessed, which has led to the development of a mild onion certification.

(DPI) postharvest researcher, Dr John Golding said the lack of a reliable, cost-effective test has been the major barrier to developing an Australian mild onion industry.

Golding concluded it is possible to consistently grade onions according to taste, after carrying out research with Food Science Australia in Sydney and at the Wagga Wagga Agricultural Institute.

Using a specially constructed onion press, NSW DPI researchers measured levels of the chemical pyruvate — which causes the distinctive pungency — in 1500 onions.

These levels were then cross-checked against rankings collated from a sensory tasting panel and more than 100 consumers.

"As expected, onions with the lower levels of pyruvate were equally 'liked' and those onions with the higher levels of pyruvate were equally 'disliked'," Golding said.

Golding recommends that mild onions be consumed no more than 30 days after harvest, since pungency increases with storage.

Pungency also varies with differing soil types and nutrient levels, making it necessary to collect onion samples for testing just prior to harvest.

Onions with pungencies close to the limit for the mild classification may need to be tested 30 days after the pre-harvest test, while those with lower pungency may not need re-testing if sold within 60 days of the pre-harvest test.