Woman patching salmon cans on an assembly line; exhibit displays section of cannery line used to move cans through the assembly line.

Left: A Diamond NN Cannery patcher uses scissors to remove fins, bury the skin, and trim bones that might obstruct the seam, ca. 1989. Katherine Ringsmuth private collection. When cooked, salmon bones soften and provide nutritious calcium to canned salmon. Right: Gallery view – photograph by Brian Wallace.


The once entirely hand-packed process of canning salmon was almost fully automated by the 1920s.

Canners introduced the conveyor belt in 1881 to make the process faster, more efficient, and linear. But it was the passage of the Chinese Exclusion Act in 1882 that compelled canneries to mechanize the canning process.

Technological Innovation

Innovation and new machinery continued to speed up the canning process. The steps involve a series of machines that developed over time.

A large cylindrical machine, which emulated the strokes of the Chinese butchers, cut the fish into can-sized sections with rotating gang knives. The filling machine automatically filled cans with salmon and a precise amount of salt at a rate of 200 per minute.

In 1903, canners replaced old hand scales with weighing machines that detected underfilled cans and automatically diverted them from the assembly line to the patching station.

A clincher attached the top of the can loosely to the body, allowing air in the can to escape.

After a series of automatic washings, the cans pass through a vacuum seamer, which extracts the air and fastens the cover on tightly with a double seam or crimp, replacing the need for solder.

The introduction of the double seal also prevented the need for a second cooking in the retort.

The Early Essential Workers

Canners relied on highly skilled Chinese workers to conduct nearly all tasks required to can salmon. The Chinese workers received the fish on the dock and tossed the salmon into bins from the boats. Chinese butchers cleaned virtually every salmon by hand—about three to six per minute.

Chinese men fed the cleaned salmon into the cutting machine, which sliced the salmon transversely in sections to the exact length of the can and the filling machine, which filled the cans with salmon. Chinese inspectors carefully weighed the cans, adding ‘patch,’ or small pieces of salmon, to the lightweights.

Expert Venters

In the early days, the cans were cooked twice, once for 60 minutes, then from 70 to 80 minutes in the second round. In between, the cans went through a process called “blowing” or “venting” to relieve pressure within the can during the first cooking that could cause it to burst.

While machines topped the cans with lids, crimped the edges, and partially soldered them into place, Chinese tinsmiths tapped rapidly the top of one can after another, making a small hole in each that allowed the steam inside to escape. After ‘blowing’ out the air, the vents were immediately re-soldered, and the cans placed back in the retort for the final cooking.

The Critical Role Tester

After cooking, cans were again checked for leaks. The testers were experts at this technique. As U.S. Fish Commissioner Jefferson Moser observed, “With a tenpenny nail they pass rapidly over the cans, striking the top of each, and judge by the sound whether there were any defects.”

The cans were placed in large open trays, lowered into a square wooden tank filled with hot water, and inspected for leaks. Canners relied on the experienced eye of the Chinese tester, who detected a faulty can by the escaping air.

The defective can was removed and placed aside with a pair of tongs, where additional solderers quickly remedied the flaw.

The Can Shop: Making Cans

While the fish house feeds the canning lines with butchered salmon, empty tins flow into the cannery from the can shop, situated on the building’s top floor. The can-making process took place on the second story so gravity could move the cans into the canning line below.

The Sanitary Can

In the early days of the salmon industry, Chinese cannery workers cut cans from tin sheets and soldered all cans by hand. The introduction of the ‘sanitary can’ in 1904 eliminated the use of lead solder to attach the tops and bottoms of the cans. Canners considered the new can-making method a revolutionary innovation.

Around 1917, The American Can Company, the nation’s largest producer of tin cans, collapsed the can bodies and shipped the “flats” to the cannery. A machine called a “reformer” reshaped the flat tins into perfectly rounded cylinders in the can shop, and then a second machine attached the bottoms. The style became known as the three-piece can with its side body, bottom, and top.

Salmon packers expressed interest in the new technology only after the 1906 development of a double seamer that closed thirty cans per minute. Advertisements in 1917 implied that sanitary cans had vanquished the “old-style soldered cans.”

Two-Piece Can

In the 1980s, the introduction of the two-piece can, which included the side body and bottom stamped from a single sheet of metal, eliminated the time-consuming re-forming process. The formed can bodies were slightly tapered to allow the cans to be stacked like ice cream cups. This reduced labor even further and freed up shipping space for the trip north to Alaska.