Gloved hands laying whole sardines head-to-tail into an open rectangular tin on a stainless steel table lined with rows of empty tins, with a tray of brined fish and a jug of olive oil nearby

A Day at the Cannery: How a Sardine Becomes a Conserva, Hour by Hour

The difference between a good tin of sardines and a great one is decided in about eight hours, most of them before lunch. The fish is at its best the morning it is landed, and the traditional canneries of Portugal and Galicia are built around that fact: buy at dawn, process by afternoon, seal by evening. Almost every step can be done by machine, and the industrial plants do them that way. The artisan houses whose tins fill our shelf still do the important ones by hand, and once you have seen why, the price of a tin makes sense. This is the day, hour by hour. For how the tin came to exist at all, our history of tinned fish is the prologue.

Before dawn: the auction

Sardine boats fish at night, when the shoals rise, and land at the port at first light. The cannery's buyer is at the auction hall, the lota, by five, looking at the catch: fish should be bright-eyed, firm, silver without bruising, and ideally of a uniform size, because a tin holds a fixed number and the packers need fish that fit. Fat content matters and changes with the season; sardines are leanest in spring and fattest in late summer and early autumn, when the best tins are made. The buyer pays for the boxes, and they are on the cannery floor within the hour. In Galicia the same routine applies to the shellfish landed from the rías, which our Conservas de Cambados guide describes.

Morning: cleaning

Each fish is beheaded and gutted, and at the artisan houses this is done by hand, with a small knife and a twist, at a speed that takes years to learn. Hand cleaning keeps the belly intact and removes the guts cleanly, which matters because a torn fish falls apart in the tin and a badly gutted one turns bitter. The cleaned fish are rinsed and go into a brine, a strong salt solution, for a period the cannery adjusts to the fish's size and fat: long enough to firm the flesh and season it through, short enough that the finished tin is not salty. This step is where the salt in a good sardine comes from; no salt is added later.

Late morning: the first cook

Brined fish are laid on grids and cooked once before they are packed, so that they lose water and set. Traditionally this was frying in olive oil, and a few houses still do it; most now steam, which is gentler and keeps the fish whole. Some producers grill or smoke at this stage, which is where the Danish and Breton smoked tins get their character. After cooking, the fish rest and dry on the grids for an hour or more. A sardine that goes into the tin wet will make a watery, cloudy oil; the drying is what gives the finished tin its clear, golden liquid.

Midday: the hand pack

This is the step that separates the tins on our shelf from the tins in a supermarket. At a stainless steel table, packers, in Portugal almost always women, and often the daughters and granddaughters of packers, lay the cooked fish into open tins by hand: head to tail, skin side up, belly to belly, the exact number the tin was designed for, trimmed with a small knife so the tails do not fold. A skilled packer fills hundreds of tins an hour and can tell by touch whether a fish is too soft to use. The arrangement is not decoration. Fish packed tightly and evenly cook evenly in the sterilizer, hold their shape, and come out of the tin whole. Machine-packed sardines are dropped in loose, which is why they arrive broken and why the oil is full of fragments. When a label says hand-packed, this table is what it means.

Early afternoon: oil, sauce and seal

The packed tins move down the line to be filled: extra virgin olive oil for the classic, or a sauce, tomato, escabeche, lemon, chile, or the Azores butter we wrote a whole guide about. The quality of the oil is the second biggest decision after the fish, because the tin will sit in it for years and the fish will absorb it; our guide to the oil left in a tin explains why it becomes an ingredient in its own right. The tins are then lidded and sealed by a seaming machine that double-folds the lid onto the body, the one step every cannery automates, because a bad seal is dangerous and a machine seals better than a hand ever could.

Afternoon: the second cook

Sealed tins go into an autoclave, a pressurized steam cooker, and are heated to above 240°F for long enough to sterilize the contents completely. This is Nicolas Appert's discovery of 1810 in its modern form. The cook does two things: it makes the tin shelf-stable for years, and it softens the sardine's bones until they are edible, which is why a tinned sardine can be eaten whole and a fresh one cannot. The exact time and temperature are each cannery's own; too little and the tin is unsafe, too much and the fish turns to paste.

Evening and after: rest, and years of it

The tins are cooled, washed, dried, and set aside. The best houses do not sell them immediately. A tin of sardines in olive oil improves for months and often years as the fish and oil exchange flavor and the flesh relaxes; Portuguese canners talk about vintages, and some tins carry the year on the base. Our guide to storage covers the other end of that timeline. Only then are the tins wrapped, often in the illustrated paper that made Portuguese conservas a design object, and shipped.

What each step tastes like

Firm, intact fish: the dawn auction and the hand cleaning. Clean salt without harshness: the brine, judged well. Whole fish, not fragments, in a clear golden oil: the drying and the hand pack. Edible bones and a soft, rich texture: the autoclave. Depth and roundness: the years in the tin. A cheap tin skips or shortens most of these and tastes like it. A great tin is a full day of somebody's skilled attention that you can hold in your hand, which is a bargain at any price on our tinned fish shelf. Taste the difference at a tinned fish tasting, or at 263 Josephine Street in Cherry Creek, Denver. Everything ships nationwide from theambrosianpantry.com.

Sources & Further Reading

Back to blog