On a rainy Saturday in Hong Kong, chef Sandy Keung leads me through the kitchen at TABLE. Her team is putting the finishing touches on an elaborate menu for a private event. Among Hong Kong's most respected seafood restaurants, the contemporary address is best known for its east-meets-west flavors, raw oysters, assorted shellfish, and hand-made pasta. But I've come to see the restaurant's most prized possession.
We turn a corner and there it is—the depuration tank. It's totally unassuming, boring even. It just looks like any old fish tank, except for one noticeable difference: the water is crystal clear. In a city where locals eat fish for breakfast, lunch, and dinner—cheeks, heads, eyeballs, and all—the depuration tank, and the resident marine biologist who constantly monitors the animals and adjusts the chemical levels, is what sets TABLE apart. Both are firsts in Hong Kong, and are in response to the they city's increasing reliance on imported seafood.
In particular, live imported shellfish—oysters, crabs, lobsters, clams, and mussels—arrive dry, stressed out, and full of metabolic waste and bacteria. The depuration tank is a seawater treatment system that decontaminates shellfish over the course of at least 24 hours, using a combination of 100 percent recycled water and ozone that's formed by sending an electric charge through a pump in the water, creating O3 from O2. After the purification process, the ozone returns to O2, and any discharge is fed into an attached container. Basically, the setup is equal parts shellfish spa and sewage center.
Hong Kong consumes more seafood per capita than anywhere in Asia besides the Maldives, eating around 150 pounds per person, per year. That's roughly three times higher than the global average. Like the rest of the world, Hong Kong's relationship with seafood is growing increasingly complicated.
Historically, Hong Kong was home to a thriving fishing community. Around the 60s and 70s, the industry hit a peak with introduction of bottom-trawling vessels. But this caused fish stocks to deplete rapidly, forcing fishermen to travel farther and farther to catch the same quantities. Eventually, the trade faded out , and there are now only a couple thousand fishermen left today. While a legacy of seafood restaurants remains, fishermen are few and far between. These days, the city imports 90 percent of its seafood. But locals tend to consume a larger variety of seafood than in the US, where the top three types of seafood—salmon, tuna, and shrimp—make up more than half of total consumption.
Such a heavy reliance on imports means that a typical seafood supply chain can have nearly a dozen links. "So many people have handled seafood from the source to your plate. Anything can go wrong at any one of these steps," says Keung.
For diners, that could lead to consuming contaminated seafood laden with bacteria, pollutants, and heavy metals. Dangers of serious illness aside, a buildup of metabolic waste and contaminants will also smell and taste funky. You know that "overly fishy or clammy" flavor some seafood has? According to Keung, you can credit that to contamination, not the animal itself.
Before she owned a restaurant, Keung was a businesswoman who invested in a land-based fish farm, which gave her behind-the-scenes insight about the inner-workings of the seafood industry. "The moment I decided to deal with seafood in the restaurant, [the depuration tank] was a no-brainer for me," she explains. "Once you have seen the light, you cannot go back."
Depuration makes seafood safe to eat, but it also makes it taste better too. A few days of post-travel hydration and relaxation makes bivalves and crustaceans taste fresher, plumper and juicier.
"If an oyster leaves the water for three or four days, it feels it," Miller Tse, TABLE's resident marine biologist explains. "An oyster undergoes something called 'programmed cell death.' The animal thinks it's going to die when it's being shipped, so it starts preparing for death. This affects the texture and the metabolism of the oyster, making it produce more toxins."
The depuration tank provides a place for the bivalves to relax, use the bathroom, and detoxify. Once the animals calm down, they open up and naturally filter out harmful bacteria, ammonia waste, solid waste, heavy metals, and microorganisms, which means you can eat that oyster without the fear of hugging the toilet bowl the next day—or worse, getting infected with nasty diseases or viruses.
The process requires specific levels of salinity, temperature, and ozone—each depending on the type of animal in the tank. If the levels are off by a fraction, it can kill the crustaceans. Due to cost involved, restaurants don't usually invest in depuration tanks, and due to the risk, many large-scale commercial suppliers skip this step and distribute the seafood without proper purification, Keung says.
A reliance on imports isn't going anywhere, and fish farming creates a lot of pollution and contaminants. Scanning the relatively concise menu at TABLE, I tally up more than a dozen types of seafood from every corner of the world—French blue lobster, live "Flower" crab from the South China Sea, Hokkaido uni, Spanish red prawn, mud crab, crab sashimi, tua tua surf clams, and oysters from every corner of the ocean.
While installing a depuration system ensures clean, disease-free seafood for diners, it only addresses the final step in the supply chain. And let's face it: hiring a marine biologist and investing in a depuration tank will probably never be economically realistic for most restaurants. The industry is facing a turning point. Global seafood consumption hit an all-time high earlier this year, sailing above 44 pounds per capita for the first time, and the pressure on supplies will only increase as the world welcomes another 2 billion people by 2050.
The reality is that Hong Kong is the rule, not the exception—imported farmed fish is the future and, in many places, it has already well surpassed wild fish stock. The US already imports roughly 90 percent of its seafood, most of which comes from Asia, where aquaculture practices have a reputation for skirting regulations. As farm-raised fish starts taking up a larger portion of restaurant menus and seafood sections of grocery stores, consumers will need to seek out more transparent suppliers or seriously reconsider their consumption habits.
"People want to know that the path is sustainable and the fish have been treated well along the way," says Monica Jain, founder of Manta Consulting and Fish 2.0, a sustainable seafood startup competition "The problem is that the longer the supply chain gets the harder it is to know."
With that in mind, Keung has chosen to focus on sourcing TABLE's seafood from the best possible suppliers, and keeping the menu varied, rather than just curating a menu based on fish deemed to be "sustainable" or "organic."
"When it comes to seafood, (the word 'organic') is not straightforward like farmed plants or animals. The same goes for 'sustainable,'" she says. "People care about seafood quality from a health perspective. There are fewer people in my clientele who are worried about sustainability and overfishing. They aren't asking about environmental costs. For a while I did actually label items that were sustainable, but I didn't notice if people were pointing at it that it was certified sustainable."
Until consumer habits shift, and they start holding themselves—as well as suppliers—responsible for what they're eating and the impact it has on the environment, Keung will continue keeping an eye toward doing what she can to ensure that her customers get the best product available.
"We try to do whatever we can," she says. "That's where the depuration tank comes in. That's the last bit we can actually do."
Every day this week, MUNCHIES is exploring the future of food on planet Earth, from lab-grown meat and biohacking to GMOs and the precarious state of our oceans. Find out more here.