a mixture of fruit and sugar boiled together, poured into jars, and sealed to give a long-keeping preserve with a wet semi-solid consistency, known to a food scientist as a gel. There are distinctions to be observed beween jam, where the fruit is almost formless and the texture is thick yet almost flowing; jelly, where the fruit is strained for its juice then cooked with sugar and gelled (and which in the USA is a frequent colloquial usage for jam); marmalade, which in England means citrus jam with peel, but in France may mean a fruit paste or cheese; and conserve or preserve, where the fruit is in almost its original form, cooked in a very thick syrup. Such things are based on widespread and ancient methods of preserving fruit. Similar confections are made throughout Europe and the Middle East. Although the ancient world knew about preserving fruit in honey—the ancestor of quince cheese, melomeli, mentioned by Columella is an instance—jams and jellies needed cane sugar to become a kitchen staple.
Successful jam depends on the interaction of three things in the correct proportions: sugar, pectin (long chainlike molecules occurring in the cell walls of plants), and acid. Fruit contains all of these, but the jam-maker always adds more sugar, and sometimes pectin and acid.
Sugar is usually added to the mixture in the proportion of 1:1 by weight sugar to fruit pulp. It has two functions: it sweetens the fruit, and it plays an important part in gel formation. Sugar is highly attractive to water molecules and ‘binds’ them in solution. This leaves less water available for the pectin to form bonds with. Instead, the pectin molecules link to each other, forming a network which traps the sugar and fruit pulp. Acid encourages this process: normally pectin molecules carry a small negative electrical charge in water and therefore tend to repel each other. The function of the acid is to reduce the electrical charge. So when a jam mixture cools, the chainlike pectin molecules bond to form a network, holding the sugar solution and fruit pulp in what appears to be a solid mass.
Certain fruits are recognized by jam-makers to need additional acid or pectin to produce a satisfactory result. Strawberries are a good example: they contain little acid and weak pectin, and are notorious for a ‘poor set’. Extra pectin, extracted from apples or citrus fruit, can be added; and home jam-makers are usually instructed to add lemon juice as well.
The optimum conditions for producing a good jam are: a sugar concentration of 60–5%; a pectin content of 0.5–1.0%; and a pH of 2.8–3.4. Stated like this it seems remarkable that anyone should produce jam successfully outside a laboratory; but centuries of trial, error, and experiment with gluts of acid fruit such as gooseberries have fixed jam firmly in the affections of the British.
The word jam is a newcomer. Its derivation seems an abiding mystery. The OED suggests its source is the verb ‘to jam’, to bruise or crush by pressure, which makes its first appearance in 1706. Yet the historian David Potter has found a plum jam recipe in a manuscript belonging to the family of Ann, Lady Fanshawe that must date ‘some years before 1708’, although the word does not enter the printed record until the first edition of Mrs Mary Eales' Receipts in 1718. This makes OED speculative at best.
The preserve we now recognize as jam has moved quite a long distance from the rather solid fruit and sugar conserves, preserves, and marmalades of the 17th and 18th centuries. The development which took it to the soft spreadable paste was the increased understanding of hygiene, such as the necessity for clean processing and for sealing the jars, that developed in the 19th century.
Even then, jams were a luxury, as sugar was not cheap. Mrs Beeton (1861) observed, ‘It has long been a desideratum to preserve fruits by some cheap method … The expense of preserving them with sugar is a serious objection; for, except the sugar is used in considerable quantities, the success is very uncertain.’
In modern Britain, jam is cheap and commonplace, and is usually eaten as part of a meal such as breakfast, or a snack, with bread or toast. It is also used as an ingredient in baking, for instance: spread between layers of cake; used as a glaze on open fruit tarts; as a filling in jam tarts and doughnuts; and as a layer in some puddings, for instance, Bakewell tart. In its industrial production, Britain probably led the world. So much so that jam became an staple of working-class diet at the end of the 19th century. Per capita consumption was around 10 lb per year (Johnston 1977) and George Orwell's The Road to Wigan Pier (1937) is eloquent about its importance. In fact, greater affluence has led to a decline in its popularity, even if the quality has improved.
Jam manufacture is widespread in all industrialized countries and a frequent article of international commerce, converting surpluses of fresh produce into a readily transportable commodity. It has also become an important showcase of artisan skills for small producers both here and abroad.
The distinctions made above between different consistencies are also made in Russia, and described by Lesley Chamberlain (1983). These are, ‘varen'ye, which should contain large chunks of fruit or whole berries and has plenty of syrup to spare, dzhem (from English jam), which is firmer, often set with pectin, and made of puréed fruit, and povidlo, fruit jelly or cheese’.
Varen'ye is used in baking, and as a dessert on ice cream, and on curd cheese. It is also taken with tea, being served in a small dish and eaten with a spoon. This use of jam as an accompaniment to drinks is also common in the Middle East and E. Europe (see gliko). Claudia Roden (1968) describes the use of jams in Levantine rituals of hospitality. Pastries and jams, in crystal or silver bowls on trays,
were arranged around the spoon stand, next to which was placed a glass of water … The trays were brought round to each of us in turn as the coffee was served, for us to savour a spoonful of each jam, or more of our favourite one, with one of the little spoons, which was then dropped discreetly in the water.
Jams were also used as desserts, or to flavour a glass of drinking water.
Laura Mason has written about several aspects of British food in books including Sugar Plums and Sherbet (1998), Farmhouse Cookery (2005), and Traditional Foods of Britain (1999), which she co-authored with Catherine Brown.
Beeton, Isabella (1861), Beeton's Book of Household Management, facsimile of 1st edn, London: Chancellor (1982).
Chamberlain, Lesley (1983), The Food and Cooking of Russia, London: Penguin.
Johnston, James P. (1977), A Hundred Years Eating, Dublin: Gill & Macmillan.
Roden, Claudia (1968), A Book of Middle Eastern Food, London: Nelson.
