We have been used to seeing cheap canned foods on supermarket shelves all the year round for decades. With southern Europe just one of the many regions suffering record temperatures and drought around the world, it is timely to look at the possible impact on food products that we have relied on for centuries. It is necessary to distinguish canned foods that have an underlying seasonality, in other words, a point in the season at which the given food is plentiful.
Foods such as canned peeled plum tomatoes, canned salmon, or canned green beans, are packed during the peak cropping weeks of the season. Dedicated canning and cooking lines operate 24/7, with a scaled up version of a process that Nicolas Appert would recognise instantly. In the case of wild salmon, the canneries are located next to the rivers and are stocked up with empty cans ahead of the season. When the salmon return to spawn, fishing crews join the serried ranks of predators that are attracted by thousands of fish in breeding condition.
The standard cooking unit on such lines are a large tank of water, similar to a swimming pool, but kept at a rolling boil for the duration of the pack, which can last weeks. As the fish are caught and brought to a salmon cannery, they are prepared and the cans are filled before cooking. The duration of the cooking time is regulated by a crawler belt that covers the floor of the cooker. Small 100 gram cans are shifted through the cooker during the day at relatively rapid speeds, since they need less cooking than larger cans.
In the case of peeled plum tomato canneries, can sizes go up to 3kg. Lorryloads of raw tomatoes are delivered during the day, some of which will be kept for the night shift. When they clock in, they start filling 3kg cans while the crawler belt is slowed down to its slowest setting. By the time the day shift returns, there will be large stacks of packed and cooked 3kg cans. There will also be a steady stream of lorries laden with tomatoes for the day shift as the belt at the bottom of the cooking tank returns to its daytime setting.
This kind of production line depends on high volume intakes during a clearly-delimited number of weeks (salmon canneries generally pack more than one kind of salmon). It is vulnerable to seasonal variations and crop failures. A bit like us, really. There is an important distinction to make for peeled plum tomatoes, which is that these are mainly grown and packed in Italy. Unlike chopped tomatoes or tomato paste or passata, the cannery can only pack intact tomatoes. These are an industrial variety that are not useful for any other product.