How canned soup is made

Condensed soup has half its water taken out, so one can holds two cans' worth for the shopper to dilute at home.

stations: 9
things upstream: 63
raw sources: 23
steps from the ground: 9

The short version

Vegetables are washed, peeled, diced and blanched while stock simmers from bones and meat in steam-heated tanks. Everything is blended to a fixed formula with heat-stable starch, filled hot into cans with a little headspace and sealed with a double seam. Sealed cans go through a retort or steam tower that kills botulism spores, then cool quickly under controlled pressure. Condensed recipes leave out about half the water.

Simmer the stock

Bones and meat simmer in water in stainless steel tanks heated by steam. The broth stays separate until the blend.

Goes in
Chickens Water
Clean and dice vegetables

Vegetables are steam cleaned, peeled and diced to an even size, since oversized pieces heat unevenly in the can later.

Goes in
Tomatoes
Blanch the pieces

A short spell in hot water or steam at about 95 °C stops the enzymes that would spoil color and flavor before the cans are heated.
Blend to formula

Solids, stock, salt and seasoning combine in a steam kettle or ribbon blender. Modified starch thickens the batch because it survives sterilizing heat without breaking down.

Goes in
Corn starch
Fill the open cans

Soup at 60 to 85 °C goes into coated steel cans, leaving a gap of air at the top. A jet of steam can clear that gap just before the lid goes on.

Goes in
Tin can
Double seam the lids

A seamer folds the lid edge and can edge together twice to make an airtight seal. Cans are pulled off the line often so the seam can be measured.
Sterilize under pressure

Sealed cans ride through a retort, rotary cooker or hydrostatic tower of steam. The time is worked out per product so heat reaches the center and destroys botulism spores.

110 to 130 °C
Cool the cans

Treated water brings the cans down fast so the soup stops cooking. Pressure drops gradually at first, or hot cans would deform.
Label and pack

Cooled cans are labeled and cased for shipping.

End of the lineCanned soup

Worth repeating

Sealed canned food typically lasts one to five years, and in special conditions much longer.
Andy Warhol painted a series of 32 canvases of soup cans in 1962.