What Happens When You Age Fish?

Would you eat fish that's over a week old?

Sorry to break it to you, but you're probably doing just that on the regular without even knowing it.

It all started with slime. Seafood legend John Bil and I have been spending a lot of time together as he introduces me to all the aspects of the world of fish and shellfish that the majority of us shrimp ring eaters know nothing about.

A while back he aged a halibut. "Aged?" I asked, picturing withered steaks or wheels of cheese. He took the whole fish, slime intact—"the slime is important," he said—and aged it for 16 days. He then fileted it, cooked it up, and ate it. He looked at me from under the brim of his ballcap and said, "Let's do it again and invite some friends."

Bil ordered a halibut and set it to age in the fridge at his shop, Honest Weight; then, a week later, he ordered another and stored that to age as well. He planned to get in some more fresh halibut a week after that, when we would have a lunch at which he'd serve all three for everyone to taste and compare.

Will this be the beginning of a movement in which chefs are hanging and aging fish, bringing briny funk to the umami tasting table?

So I invited a mix of people from Toronto—a James Beard award-winning cookbook author; a yoga-addicted, chain-smoking chef with six popular restaurants; a woman who oversees five hundred employees as director of operations at one of the city's larger restaurant groups; the head of PR for one of North America's big publishing houses; and a sommelier-at-large. All they know is that Bil will be serving old fish for lunch.

Chef Anthony Rose, who owns those six aforementioned restaurants, imagined the fish would be cured. Being Jewish, he thought of smoked salmon and gravlax, much like what he serves at his Schmaltz Appetizing deli counter.

Christina Kuypers is director of operations for Icon Legacy Hospitality, where she oversees ten restaurant properties in Toronto, Miami, and Dubai. Her heritage is a mix of Filipino and Dutch, so she's imagined something more along the lines of pickled herring, or maybe the pungent fish served with vinegar in the Philippines.

Naomi Duguid—a prolific cookbook author whose seventh book, Taste of Persia, hit shelves this month—was under the same impression as me: "I thought it was a hung meat thing."

Rob Firing, from HarperCollins Canada, and Will Predhomme, formerly the sommelier at Canoe and now an independent consultant, both mentioned lutefisk, the notorious Nordic whitefish preserved in lye, and the rotten shark of Iceland known as kæstan hákarl.

Bil stood at the head of the table and waved all this chatter away. This isn't about preserving fish indefinitely. This isn't about smoking or pickling or curing fish. It's not about dry-aging fish like a steak, and it certainly isn't about burying fish in the ground for 12 weeks as they do with that rotten shark.

He explained how most of us think when buying fish: When did that trout come in? What's the freshest?

"Those questions force the chef or the fishmonger or the server to lie to you. We live a thousand miles from the closest ocean. The fastest you are going to get a fish into Toronto from the ocean to the table is maybe three but more likely four or five days. You never hear in restaurants, 'Our fish special tonight is week-old halibut,' but that's the truth."

To understand how little we understand, here is what happens when a fishing boat in British Columbia sets out to catch halibut. Boats go out early on Monday morning and catch fish all day; they come in that evening and the fish is iced down but not necessarily processed. The following morning, the fish is processed and put on a truck that takes it to a packing facility. It is now Wednesday. On Thursday morning, the fish are put on a plane and arrive in Toronto by that night. The fish gets to your primary fish distribution centre on Friday morning. Bil would pick up the fish midmorning and have it broken down and in the display case at his Junction fish shop by Friday afternoon.

"The best case scenario is a four-day-old fish," he explained. "That isn't unique to me—that's standard in the industry. That's how it works with seafood retailers across the middle of North America: Chicago, Toronto, Calgary, Pittsburgh, Cleveland."

Needless to say, we were all surprised. Bil continued.

"My goal today is to serve you three vintages of fish: 16-day-old halibut and seven-day-old halibut from Prince Edward Island. They'll be served alongside a fresh fish that came in overnight from Boston and is fluke, similar to halibut, and is probably three days out of the water."

He added, "I think it's important that we understand there really is no perceptible difference between three days and seven days. At seven to 16, there is a difference but it's not terrible. It's still fish that I would say gets served a lot."

Bil explained that the fish were stored whole, slime on. He doesn't store the fish on ice because direct ice contact will accelerate the deterioration. The natural slime's importance cannot be understated.

"Halibut mucus contains several protective compounds, including antimicrobial peptides which are natural proteins that inhibit microbial proliferation," said Dr Gerry Johnson, the director of science at Halibut PEI, when I emailed him a few days later to ask about the slime. "In a cool (ice or refrigerated) environment they will protect the fish for many days. The mucus is easily washed off just before cooking."

At the lunch, Bil passed around a tray holding the 16-day-old halibut, skin, and slime intact. Rose sniffed the slime and tasted it, then nodded approvingly. "I'll take one with extra slime."

Duguid tried it too and agreed with him. "It has a lovely seaweed taste."

"With filets they would deteriorate more quickly," Bil said. "I order as much whole fish in as I can; it protects the flesh longer. So even though the filets I'm selling in the case came in today, they might not be as tasty as the seven-day-old halibut that's been stored as a whole fish. Flavours do develop with time."

As we tasted the three different ages of fish, which had been pan-fried and served simply with a wedge of lemon, it became obvious where the flavour was.

"The really fresh one," said Kuypers, pointing to her plate, "it really doesn't taste like anything."

The oldest one had a touch of funk but nothing off-putting; the middle one, aged one week, tasted like all the halibut I've ever had. The week-old fish was the norm.

"Foodie culture is so obsessed with farm-to-table and we're lurching toward a kind of understanding about fish, where we are finally talking about sustainability. But we've made this jump without even knowing the basics of how the fish get caught and processed," Bil explained.

"How are we supposed to decide what's sustainable and what isn't when we don't even know the first thing about the fish itself, something as simple as the age it is when we pick it up at the store?"

We don't question age on our meat, we know butchered flesh can remain intact and tasty for a certain length of time.

We need to extend the same thinking to fish. Week-old halibut for everyone!