Getting jam to set depends on pectin. Pectin, combined with the acid in the fruit and the sugar you add, makes the Jam gel. Pectin needs to be added both for fruits that are very ripe (because they will have lost most of their pectin), and for fruits that never contain any great amount of pectin, such as strawberries.
Freezer jam generally needs no cooking. While many people dismiss it as not being real Jam, others say that because the fruit doesn’t go through a boiling process, the fruit retains a more fruity, original flavour.
Jam differs from jelly in that jellies are clear — to make a jelly, the fruit is mashed and strained, so that just the juice is used, with no apparent bits of fruit remaining, whereas jam are are made from puréed fruit, and so will have small pieces of the fruit still visible. Jams are also less firmly set than jellies.
Jam differs from fruit preserves in that fruit preserves will have much larger pieces of fruit available, and fruit preserves may or may not use pectin — the fruit preserve may aim to be spoonable as a dessert, rather than spreadable like a topping, as jam is.
Jams can be made with or without added pectin.
A popular commercial brand in North America and the UK is “Certo”, though it’s actually two separate products now.
Other popular brands include Ball and Bernardin.
Some jams such as apricot and strawberry would be pourable rather than thick and gel-like without the added pectin.
When you’re not using pectin, you definitely want to try to be using some unripe fruit, about 1/4 of the fruit that you are using, as unripe fruit has more pectin and will help to give a firmer set. If you have a fruit with high enough pectin in it, such as apples, blackberries, crab apples, cranberries, gooseberries, grapes, plums, red currants or quinces, you can easily make a jam with no added pectin. Basically just mash the fruit, and measure the mashed fruit: add an equal amount of sugar, and simmer, stirring frequently, until it thickens into a jam. (Remember, it will thicken even more when removed from the heat and allow to cool.)
If you want to swap in honey for some of the sugar, swap no more than 1/4 of the sugar for honey — honey’s more pronounced taste can make your jam taste less like the fruit it is made from, and too much honey will inhibit the jam from setting because it does add additional liquid.
Don’t double a jam recipe, unless the commercial pectin you are using clearly says it is okay to. It’s much harder to get it to boil properly; and can affect how it sets. The cooking pot should be half full.
If a jar of jam develops some mould, always throw the jar out — don’t just remove the mouldy part and keep on eating the rest. Some moulds can produce potentially harmful toxins, and even if only a small part of the jam has got mouldy, there may be invisible spores not germinated yet in other parts of the Jam.
Forms of jam have been made for millennia — it just depends on how finely you want to slice the definitions of jams, jellies and preserves. The Roman writer, Apicius, has recipes for fruit preserves.
Certainly, though, it wasn’t until the modern availability of affordable cane sugar that Jams really took off.
Smuckers Jam began with Jerome M. Smucker’s cider operation in Orrville, Ohio, in 1897. He later branched out into apple butter, and then into jam.
The most famous brand in North America of Grape Jam is Welch’s. Welch’s, which already existed as a grape juice company since 1869 (see entry for Concord Grapes), got their patent for the Jam in 1917; they called it “Grapelade”. The government purchased every bottle he made and shipped it off to soldiers. The troops came home with a taste for it, and created an instant market for what would become Welch’s Grape Jam and Welch’s Grape Jelly.
In 1940, the US Food and Drug Administration set a legal definition of what a jam is.
When the Titanic went down it was carrying 1,120 pounds of jams and preserves.
In February 2009, Marks and Spencers announced that it would sell jam sandwiches as a recession special. Called “Simply…Strawberry Jam Sandwich”, it went on the market at 79p. Marks and Spencers said that a jam sandwich is “one of the greatest simple pleasures of life.”
“Marks & Spencer to sell jam sandwiches.” London: Daily Telegraph. 18 February 2009.