​​Depuration of shellfish​

Depuration is a controlled process that reduces disease-causing microorganisms in live shellfish. After harvest, shellfish are placed into tanks of clean, treated water so they can purge any microorganisms from their digestive systems.

This page provides an overview of depuration requirements. For the full requirements, refer to the NSW shellfish industry manual (PDF, 647 KB).  

Licensing and approval

Commercial depuration operations must be licensed by the Food Authority. Licence approval conditions are strict because depuration must be done correctly to ensure shellfish harvested from ‘Restricted’ waters are safe to eat.  

Before approving an operation, the Food Authority’s NSW Shellfish Program will assess the source of the shellfish, the design of the facilities and how the depuration process will be managed.

Depuration requirements

Businesses must:

• source shellfish from areas authorised for harvesting for depuration
• ensure tanks and water-treatment equipment are well designed and operated to provide a continuous flow of fully treated water
• depurate shellfish for at least 36 hours
• operate each unit according to its Food Authority-approved specifications and loading capacity
• position shellfish so they can actively filter water and remain healthy.

Premises and equipment

Depuration plants must not be used for another purpose without Food Authority approval.

The premises must provide adequate space, drainage, lighting, ventilation, hand-washing and toilet facilities, water supply and pest control, as well as:

• well maintained non-toxic fittings and plumbing
• adequate security to prevent unauthorised access while it is in operation
• areas for separating depurated and undepurated shellfish.

Shellfish trays must be impervious, easily cleaned and designed to allow adequate flow through the mesh.  

Cleaning and maintenance

Tanks, trays, baskets and filters must be thoroughly cleaned between batches.

The water treatment system and associated equipment must be cleaned and maintained according to the business’s food safety management system.

Handling shellfish

Before depuration

Shellfish must be:

• protected from contamination and temperature extremes  
• healthy and free from stress  
• cleaned to remove mud and other debris without damaging the shell margins. Washing water must be of a microbiological standard equal to or better than the harvest area.

The process of heavy culling or chipping shellfish should not be conducted immediately prior to depuration as the shellfish may become stressed and not effectively purge.

Start depuration:

• within 7 days of harvest for Sydney rock oysters  
• within 2 days of harvest for Pacific oysters and flat oysters.

Pacific oysters that are gaping must be returned to the harvest area for at least 48 hours before depuration.  

After depuration

• Remove surface foam or scum, then drain water below the shellfish before removing them.
• Use clean containers to store shellfish off the ground in a cool, dry area, following the food safety management system and required temperature controls.
• Sydney rock oysters must be placed under temperature control after depuration.
• Pacific oysters, flat oysters and other shellfish must be refrigerated at 10°C or below within 24 hours.

Staff training

Operators of depuration facilities must be trained in using the equipment and caring for shellfish. They must also be able to identify problems that could affect the safety of the finished product.

Testing requirements

Shellfish testing

Test depurated shellfish from each depuration unit once every calendar month the unit is used. The E. coli result must not exceed 2.3 cfu/g.

The Food Authority recommends testing the first batch depurated each month to avoid missing a test if the harvest area closes unexpectedly.

Water testing

Water quality is critical to successful depuration. Regular samples must be taken to verify the quality of the water throughout the process. 

Failed samples

If a sample fails to meet the relevant standard in Table 2 or Table 3 of the manual, notify the Food Authority:

• by phone within 24 hours
• in writing within 48 hours, using the online Notify a pathogen detection form.

Depuration records

Keep accurate, complete and up-to-date records of:

• the start and finish date and time of depuration
• the depuration unit used
• operator’s name
• the water source
• unique batch identifier, such as the Product Record (PR) number for oysters.

Relevant sections of the Product Record identification system must be completed at the time of each depuration activity.

Keep the approved unit specifications, food safety management system and access to the Product Record identification system at the plant.

Food safety management system records must be retained for at least 2 years and be available for audit.

More information

• NSW shellfish industry manual (PDF, 647 KB)
• ​​Shellfish cultivation or harvesting  
• Requirements for wholesale shellfish wet storage​