© Denzil Green
Preserves are vegetables or fruit that are preserved, either whole or in uniformly-sized distinguishable pieces, usually in a sealed jar or tin, to extend their storage life. Many people's grandmothers used to have a cellar of preserves, on which there were shelves of jars containing pickles, relishes, pickled peppers, chutneys, jams, jellies and whole fruits that would shine like jewels when the cellar light was turned on.
Vegetables are generally pickled in an acidic liquid such as vinegar. Generally, the word "Preserves" is only applied to them when the preserving has been done at home. Commercially, a jar of pickles is just -- well, a jar of pickles.
Where fruit is concerned, the word is applied not only to fruit preserved at home, but also commercially to fruit that has been sugar-preserved whole or in large chunks. This differs from jam, where the fruit is mashed, and jelly, which is fruit boiled down and strained so that just the juice is used to make a clear and smooth spread.
The food-processing industry may be what has made Malthus's dire predictions incorrect about the human population becoming too big and imploding on itself.
Foodies instinctively sniff at preserved food, but without it, millions would die off. Perhaps them amongst that number, and if you call the preserved food "pâté" (sp) or confit, their attitude changes completely.
Up until the mid-1800s, canned goods remained a food only for the rich, as they were far more expensive than the fresh items. Preserving allowed food items to be available to chefs 12 months a year, if their customers could afford to pay for it. Before preserving and the food industry, foodies dreamt of what was out of season, and getting it had snob appeal for them. Now that even the unwashed masses can have what is out of season thanks to preserving, foodies have decided to focus instead on unpreserved food that is local and in season.
Almost all recipe books used to always contain at least one chapter on preserving food.
The Science Behind Preserves
You need to create an inhospitable environment for microbes. With vegetables, you do that by using vinegar which makes the environment very acidic and toxic for them. (You and I couldn't live breathing vinegar, either.) With fruit, you do it by sweetening the environment. Too much of a good thing, as it were. What happens is that the sweet environment attracts and retains moisture (you'll remember from the Bread entry, that this is another function of sugar or honey in bread.) The sugar draws moisture out of any microbe cells, killing many of them outright, and crippling any others. At the same time, the sugar gets drawn into the cells of the fruit, helping to firm them to preserve texture. So it's good for the fruit, bad for the microbes.
When jars of sweet preserves are opened or the seal on them is broken, water -- even just moisture from the air -- can be enough to revive those microbes that were merely crippled through dehydration, and that's why you'll get surface mould springing to life on jams. And that's why you refrigerate them once opened, so at that least the temperature isn't encouraging to them.
At the beginning of the 1700s, Denis Pepin, a French scientist, began experimenting with cooking food in sealed jars, and with putting raw food in sugar syrup in sealed glass jars. He told a German scientist, Gottfried Wilhelm von Liebnitz, about his work. Liebnitz suggested that such preserved food could be used as army rations.
Nicholas Appert, however, was the first to put the idea into commercial practice. He ran a confiserie shop in Paris from 1789 – 1795. He sterilized the food in sealed glass jars by processing the jars in boiling water. In 1804, he set up a factory to make preserved food in tin cans. He started with meat.
In 1806, the quality of his products were praised by Grimod de la Reynière in his "Almanach des gourmands". Grimod particularly noted how green and flavourful Appert's peas were. Previously, the taste of the item preserved changed dramatically because of the sugar, salt or vinegar used to preserve it. Now, with canning techniques, a taste closer to the "natural" item could be preserved. Appert's products were expensive and desirable.
In 1810, Appert wrote his book "Le livre de tous les ménages, ou l'art de conserver pendant plusieurs années toutes les substances animales et végétales." He described his experiences since the 1770s, and his hot-water processing techniques.
Appert, though, didn't use tins, but rather bottles stoppered with five layers of cork.
But Liebnitz had been right: at the time in France, the idea really only had importance for the military. France had access to fruit and veg year round owing to its warm south, and its colonies in North Africa.
The Englishman Peter Durand obtained a patent in 1810 for a cannister made of iron, and coated with tin, to preserve food in. Durand chose to experiment with metal because it wouldn't be vulnerable to the breakage that Appert's glass bottles were. The tins were made by hand from three pieces of metal soldered together: the top, bottom and the sides. A good workman might produce 6 empty tins an hour. The patent was purchased by Bryan Donkin and his brother-in-law John Hall for 1,000 pounds. John Hall also owned Dartford Iron Works, which could supply the iron for the tins, which no doubt made him doubly interested. They combined Appert's method with Durand's tin can, and two years later, they opened a food canning factory on Blue Anchor Road (now called Southwark Park Road) in Bermondsey in south London. By the following year, 1813, they were supplying the British army with tinned rations. By 1818, they were joined by a J.H. Gamble and became Donkin, Hall and Gamble. The firm was bought out by Crosse & Blackwell sometime before 1850. 
It was the Germans who took the idea and ran with it commercially. By the 1850s, the German cities of Braunschweig and Lübeck were processed food centres. A side effect was the development of farms specialising in certain crops, such as asparagus, green beans, and peas to supply the factories. In turn, it was worthwhile for inventors to develop specialized machines to plant and harvest these single crops.
What turned food preserving into a food processing industry was the massness of the scale, methods that were reliable and repeatable, and metal cans that enabled easy shipping.
On 2 October 1866, an American, J. Osterhoudt of New York City was granted a patent for a tin can that could be opened with a key.
At the start of the 1900s, tinned food was still associated with luxury items.
According to Ambrose Heath, in his 1939 book "Open Sesame: The Way Of A Cook With A Can", canned goods in the UK then offered consumers 90 kinds of fish, 97 varieties of fruit, 100 kinds of vegetables, and 218 types of meat.