Implications of fumigation and heat treatment on imported oak barrels and other products

The Department of Agriculture and Water Resources (DAWR) has announced that mandatory fumigation and/or heat treatment will be applied to high risk imported goods shipped between 1 September 2018 and 30 April 2019 as a seasonal measure to protect Australian agricultural industries from the brown marmorated stink bug (BMSB). Wood products such as oak barrels and cork have been categorised as one of a range of high risk products for biosecurity incursions and will require mandatory treatment. Other winemaking additives may also be subject to treatment through random inspection or if they are part of a consignment that contains target high risk goods.

A recent media release issued by WFA and WISA details the likely additional lead times and costs for shipment, treatment and clearance of imported products for vintage 2019. This eBulletin addresses concerns over possible implications of these treatments on oak barrels and other winemaking products.

The two fumigation treatments announced by DAWR are methyl bromide or sulfuryl fluoride. These agents have been used as insecticides for more than 50 years, mainly due to their toxicity to a wide variety of pests and their ability to rapidly penetrate into materials and then dissipate after aeration leaving minimal, if any, residue.

Winemakers may be concerned about the possibility of taints resulting from the fumigation of oak barrels. The AWRI has carefully considered the chemistry of formation of halophenol and haloanisole taints and reached the opinion that the fumigation of oak barrels with methyl bromide or sulfuryl fluoride is highly unlikely to cause such a taint unless a strong oxidising agent (e.g. hypochlorite or ozone) is also present, or unless the barrel is already tainted with a halophenol.

The AWRI’s helpdesk has not encountered any issues in the past of taints resulting from fumigation of oak barrels. However, if an oak barrel has a high moisture content, there is a possibility it could contain residual bromide (from methyl bromide) or fluoride (from sulfuryl fluoride) ions after fumigation. Consequently, it is advisable for fumigated barrels to be filled with treated (i.e. chlorine-removed) water for 48 hours after airing, to minimise the risk of residual bromide or fluoride ions.

There is also potential that winemaking additives and processing aids present in fumigated containers could adsorb methyl bromide or sulfuryl fluoride, and that it could take some time for the adsorbed fumigants to dissipate.

Heat treatment
The third treatment option put forward by DAWR is for containers to be heat treated at 50 degrees Celsius or higher for at least 20 minutes. Note that the DAWR website only lists offshore treatment providers, so it appears that heat treatment must be performed before departure from the country of origin. A possible issue arising from heat treatment is the drying out of oak barrels and the resulting potential for leakage.

What to do if a pest is found?
The AWRI advises grapegrowers and winemakers who transport or receive goods from overseas to be vigilant in checking for BMSB and other biosecurity risks. If any type of live pest is found while unpacking or moving goods, it must be reported immediately to the DAWR Hotline on 1800 798 636. If a live pest is found:

  • Collect and contain a specimen.
  • Re-seal any opened boxes, re-pack the container where possible, and shut the container doors.
  • Do not move the container, especially to an outside area.

If growers or winemakers think they have seen BMSB (or any other exotic pest) in the vineyard or winery, they should phone the Exotic Plant Pest Hotline on 1800 084 881.

For further information on methyl bromide and sulfuryl fluoride, including their chemical reactions and relevant research papers used in the preparation of this eBulletin, please contact the AWRI helpdesk on 08 8313 6600 or helpdesk@awri.com.au.

The AWRI has prepared this eBulletin based on a review of available relevant research papers. The information presented is for guidance only; the AWRI has not performed any research on the effects of fumigation on oak or other products with the above-mentioned fumigants, and therefore cannot guarantee that adverse effects will not occur. Winemakers that have concerns over residual levels of methyl bromide or sulfuryl fluoride in fumigated barrels are advised to have the barrels tested by a reputable laboratory and not to rely solely on the information contained in this eBulletin.