Depuration Tanks in Oyster Cleaning and Shellfish Safety

Here at Richard Haward’s Oysters our depuration tanks are a vital part of our operation, ensuring people are able to enjoy our incredible oysters all year round. The journey from our oyster beds to our customer’s plates isn't as straightforward as one might think. Depuration tanks are essential systems that ensure oysters are safe and clean for human consumption.

Oysters are nature's water purifiers. They feed by pumping water through their gills, extracting plankton and other particles for nutrition. While this process helps keep the surrounding waters clean, it also means that oysters can accumulate bacteria, viruses, and other contaminants from their environment. Depuration tanks, also known as purification or relaying systems, are designed to address this issue. These tanks simulate the oyster's natural filtering process in a controlled environment while providing an opportunity to flush out contaminants, ensuring that the oysters are safe to eat.

The depuration process involves transferring our freshly harvested oysters from our oyster layings to specially designed tanks. These tanks contain clean, filtered seawater that passes through ultraviolet light systems, which is in continuous circulation, each oyster filtering this clean seawater. The UV exposure purifies the oysters of anything which could be deemed potentially harmful to humans if consumed i.e. E-Coli, Salmonella, Vibrio.

So what does this process look like?

1. Oysters intended for human consumption are carefully harvested from our layings, which are in certified waters. These waters undergo rigorous testing to ensure they meet food safety standards. We test undepurated oysters from various areas where the oysters grow which gives confidence that the oysters we cultivate are coming from high quality and clean waters, which they do. We are in regular contact with our local authority, sending them test results. They also do independent testing of our product and of our harvesting beds with all data sent to CEFAS.

2. Once washed and graded, they go into the depuration facility, placed in tanks filled with purified seawater. The tanks are designed to replicate the oysters' natural environment, allowing them to filter and feed.

3. The tanks are equipped with systems that continuously circulate water, replicating the natural flow that oysters experience in their habitats. This constant circulation helps oysters expel contaminants as they feed on the naturally occurring plankton in the water.

4. Throughout the depuration process, the water quality is closely monitored. Parameters such as temperature, salinity, and oxygen levels are maintained within optimal ranges to support the oysters' health and purification. Additionally, samples of oysters are regularly tested to ensure they are clean and safe to eat.

5. The time oysters spend in depuration tanks can vary, depending on factors such as initial contamination levels and local regulations. Our oysters are depurated for 42 hours as specified by regulation EC 853/2004. During winter months we increase depuration times to 64 or even 86 hours if possible.

The primary goal of depuration tanks is to ensure the safety of shellfish consumers by reducing the levels of harmful contaminants. The controlled environment of depuration tanks provides a way to minimise these risks.

Depuration tanks offer several advantages. The primary benefit of depuration is the enhancement of food safety. Consumers can enjoy oysters without worrying about potential health risks associated with contaminants. The controlled depuration environment ensures that oysters remain alive and healthy, preserving their flavour, texture, and overall quality. We are proud of our oysters, their taste, and their quality. The depuration systems we have ensure these amazing oysters can be enjoyed by people across the UK.