Science Fair Project Encyclopedia
- For other meanings of the word "jam", see Jam (disambiguation)
Jam is a type of fruit preserve. It is a way of preserving fruit by boiling it with sugar to make an unfiltered jelly. The use of cane sugar to make jam and jelly can be traced back to the 16th century when the Spanish came to the West Indies, where they preserved fruit, but the Greek technique of preseving quinces by boiling them in honey was included in the Roman cookery book associated with the name Apicius.
When the mixture reaches a temperature of 104 °C, the acid and the pectin in the fruit react with the sugar, and the jam will set on cooling. However, most cooks work by trial and error, bringing the mixture to a "fast rolling boil", watching to see if the seething mass changes texture, and dropping tiny samples on a plate to see if they run.
How easily a jam sets depends on the pectin content of the fruit. Some fruits, such as gooseberries, redcurrants, blackcurrants, citrus fruits, apples and raspberries, set very well; others, such as strawberries and ripe blackberries, need to have pectin added. There are proprietary pectin products on the market, and most industrially-produced jams use them. Home jam-makers sometimes rely on adding a pectin-rich fruit to a poor setter; hence the popular old favourite blackberry and apple. Other tricks include extracting juice from redcurrants or gooseberries. Making jam at home used to be common, but the practice is declining, and the accessories, particularly the cellophane covers for jam jars, are becoming more difficult to find in some locations.
In the United States, jam which has been filtered to remove pulp and make it clear is called jelly. Jam which has whole pieces of fruit is called preserves, or conserves if it has nuts as well. Jam with fruit peel is called marmalade.
Joan Miro used blackberry jam as an art medium.
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