TABLE's Unique 'Depuration' Technique
Depuration of seafood is the process by which marine or freshwater animals are placed into a clean and appropriate water environment for a period of time to allow purging of metabolic wastes and biological contaminants (eg E. coli) and physical impurities (eg sand and silt). Most common seafood to be treated with depuration are oysters, clams, etc, which are most likely consumed raw.
Ozone, the powerful oxidizing agent, is added to the water to increase the efficacy of depuration. It destroys bacteria, yeasts, molds, and parasites. There are researches into the use of ozone for treating endemic illnesses caused by microorganisms where the mainstay treatment has many side effects and/or the pathogens are resistant to the drug treatment.
Ozone depuration is a non-thermal technique applied to sewage-contaminated shellfish to increase the supply of safe and nutritious bivalves. Generally considered as safe as an antimicrobial agent for use as a disinfectant or sanitizer for foods (USDA, 1997), ozone has a high germicidal effectiveness against a wide range of pathogenic organisms including both gram-positive and gram-negative bacteria, viruses, fungi, and protozoa.
Why Do Shellfish Need To Be Depurated?
Isn’t Jet Fresh Really Fresh?
Live shellfish are sent to Hong Kong from all over the world by airplane. Nonetheless, given air freight is very costly, and most shellfish can survive without water for a period of time, all shellfish are transported without the extra water weight.
How do bivalves such as oysters, clams eat and go to the restroom (ie, purge)? They are filter-feeding animals, which eat and excrete by filtering in and out water.
Many of us do not realize unless you are in the logistics business, taking oysters as example, that it takes a minimum of three days to deliver them from a French oyster farm to a restaurant in HK door to door.
If logistics takes three days, it means by the time these oysters / shellfish arrive 'jet fresh' at the restaurant, they are already three days out of water. It is like they have not been to the restroom or taken a shower for three days! And what do chefs do when they receive the shellfish? They put them into the fridge immediately to keep them alive. Yes, they are alive - but not in the cleanest or freshest of states.
The Most Natural Way to ‘Clean’ Shellfish
Ozone depuration is considered one of the most natural ways to ‘clean’ shellfish as it is non-thermal and leaves no chemical trace. Non-thermal means it does not require killing the shellfish first, unlike subzero temperature treatment or cooking at high heat.
During depuration, the shellfish filter in and out of ozonated water, rehydrate, and purge the accumulated metabolic wastes. It is a deep natural cleanse from within the shellfish, and not a mere topical sterilization such as thermal techniques (use of extreme temperatures to kill bacteria and other microorganisms).
Point to note is that depuration is carried out while the seafood is alive, and they must feel safe and not stressed in the environment. Otherwise, the oysters / clams will simply remain shut to protect themselves, and will not filter in and out water.
At TABLE, We Carry Out Ozone Depuration with All Our Live Shellfish
We carry out ozone depuration with all of the live shellfish used at our restaurant in the depuration tank maintained by our own resident marine biologist. We never serve jet fresh shellfish - shellfish arriving at TABLE are placed in our ozone depuration tank for half a day to three days before they are served.
Long History of Depuration Techniques
The commonly defined depuration process has been practiced since the 1800s originally as a method to prevent typhoid fever (via Salmonella enterica subsp. enterica, serovar Typhi) and other illnesses attributed to polluted shellfish being consumed.
Seafood depuration is legislated or regulated in many countries, including the United States, EU members such as France, Ireland, and Italy, and Japan. World Health Organization (WHO) and Food and Agriculture Organisation of the United Nations (FAO), both recognise and encourage the application of seafood depuration. This does not seem to be practiced in Hong Kong and awareness is non-existent.
Why is 'Depuration' Not Practised by More Restaurants?
The long history of depuration, which is adopted across many countries and is recognised by international agencies, is contrasted by the scarce understanding in the commercial space of the seafood industry and the lack of public awareness.
Researches, publications, and governmental regulations on the subject matter thus far in the US and Europe seem to approach depuration in the form of 'public protection' and not in the form of 'public awareness'.