Why not all red onions are mild

Onions prepared for taste testing at Food Science Australia.

Onions prepared for taste testing at Food Science

A NSW Department of Primary Industries (DPI) researcher is investigating the factors responsible for making some onions strong and others mild.

Research Horticulturalist, Dr John Golding, says variety is not a good indicator of pungency – in fact even some red onions, which are usually assumed to be mild, can be very hot.

Dr Golding is undertaking research into mild onions for the Australian onion industry, which is assessing the feasibility of categorising onions according to pungency.

Taste testing undertaken for the study with Food Science Australia in Sydney indicates that consumers prefer mild onions, and are clearly able to distinguish between the different classes of onion pungency.

Dr Golding said onions of different strength of pungency were presented to experienced trained taste testers, as well as to 100 untrained consumers who were given the same range of onion pungencies to taste.

Dr Golding said growers often assumed sugar levels were a good indicator of pungency but that this is an unreliable measure.

'Pungency is related to a naturally occurring chemical in onions called pyruvate.'

Dr Golding said low levels of pyruvate seem to be sufficient to distinguish the onions identified by the consumer panels as mild.

'However pyruvate alone does not always explain the huge range of variation between mild and strongly-pungent onions. The missing ingredient may be another natural chemical in onions called Lachrymatory Factor (LF)'.

'LF is released when an onion is cut. It is believed to be responsible for making you cry when you cut onions', he said.

This research is funded from onion growers’ levies and Horticulture Australia and aims to help the industry to market and develop the mild onion industry in Australia.

Dr Golding said the University of Georgia in the United States had developed a testing methodology for assessing onions for pungency.

He said in Georgia, there were mandated levels of pyruvate in mild onions to ensure consumers receive mild onions.

The levels are determined from onion samples collected at a rate of two 10 bulb samples per acre, in order to get a representative indication of pyruvate.

'NSW DPI can test for pyruvate levels in onions at DPI’s Wagga Wagga Agricultural Institute, where an onion press was recently built.

'However at this stage we do not know the correct sampling rate for Australian conditions.

'This is important because onion flavour is influenced by a combination of onion genetics, soils and climate.

'In Australia, we don’t yet know how Australian conditions affect different onion varieties or whether the same sampling rate would produce an accurate test', Dr Golding said.

Results from the research are being considered by the Australian onion industry and will be discussed at the National Onion Conference in Brisbane in May this year.

World experts on mild onion production and certification will talk and hold workshops on mild onions at the conference.

Further information

Dr John Golding, DPI Gosford on 02 4348 1926 or john.golding@dpi.nsw.gov.au.