A new HGCA survey has suggested the timing of harvest, drying temperature and seed handling can influence the free fatty acid content in rapeseed oil.

HGCA sought to identify the cause of particularly high FFA levels recorded in Scotland in 2012 by conducting a grower survey, in partnership with oilseed merchants.

FFAs are a concern for end users because they can make the oil unsuitable for human consumption and cause foaming in biofuels. FFA levels in excess of 2% can result in deductions to the price growers receive, reflecting the costs of removing them from the oil.

Following analysis of the survey responses, three key factors were identified as contributing to the incidence of FFAs. HGCA is planning to build on this initial work to explore these and other contributory factors leading to increased levels of FFA.

"Although this was a small, self-selecting survey, it indicates that harvesting too early or too late after desiccation can both increase the amount of free fatty acids," said Dr Simon Oxley, Senior Research and Knowledge Transfer Manager at HGCA. "Previous research suggests immature seeds in early harvest and pre-germination of seeds in late harvest increase FFA levels.

"Harvest is a busy period so getting all the crops in at the optimum time can be difficult, especially if there is a poor weather window. If growers do have to bring in their oilseed rape a little early or late they should keep in mind that the FFA content may be affected," he added.

The survey has also indicated that drying practices influence FFA content, with increased levels recorded when higher drying temperatures were used.

Dr Oxley suggested growers take this into account when selecting temperatures: "Higher drying temperatures allow greater throughput on drying equipment but can also increase FFA levels. Growers need to take care when selecting their dryer temperature and balance any risk from an increased FFA content with getting all their crops dry and in stores."

The survey also looked at whether other factors such as variety or region had an effect on FFA levels.

"The work so far hasn’t indicated significant relationships with any other factor,” explains HGCA’s Dr Ellie Marshall who was responsible for the data analysis, “But we have to bear in mind that this research was conducted in one growing season. In future we intend to expand this work and explore all possible influences on FFA levels in more detail."

Comparing neighbouring sites where FFA levels are high and low will be key to understanding this problem. Varietal differences may also be analysed using material from HGCA Recommended List trials. Care is, however, required in interpretation as FFA may vary from year to year on a particular variety as a consequence of different maturity dates.

Rapeseed is a high value crop and it is important that storage and seed handling reflect this. According to the study, ventilating stores reduces the risk from FFAs because it helps reduce the build-up of heat in the crop which is thought to contribute to the formation of FFAs.

Ventilation of stored rapeseed prior to drying and uplift is, therefore, something growers may need to consider to keep levels down.

Growers concerned about FFAs should speak to their merchant or processor about quality requirements since it is anticipated that a greater level of testing will be done in 2013.

HGCA has a range of information to support people growing and selling oilseed rape including the Oilseed sellers’ checklist, the HGCA Storage guide for cereals and oilseeds, and the Oilseed rape guide.

The full report from this research will be available soon at hgca.com/research.