What causes jam not to set?

Answer 1

There are two major reasons why jam does not set. The first reason is related to the pectin content of the fruit you use, and the second is related to the setting point of jam.

(1) Pectin - All fruits contain pectin, but some contain much more than others. As a general rule, the sweeter the fruit, the less pectin it has. For example, strawberries and peaches have very little pectin; Oranges and apples have quite a bit, and lemons have a lot. Jam needs pectin to set. If you choose a fruit like strawberries to make you jam, you must add pectin. You can buy pectin from the supermarket and add it according to the manufacturer's instructions, or you can cut up two lemons and add them to your jam. Adding lemons not only takes care of the pectin, it also gives any jam a delicious tangy edge. (Use a cloth bag for the lemon pips, and remove the bag before pouring the jam into the jars.)

(2) Setting Point - This is the other thing which can cause a problem with jam not setting. During cooking, all jams reach a "setting point." This is the point at which the jam will set when poured into your jars, and is cooled down. The trick is to recognize setting point when the jam is cooking. To test setting point, place a teaspoonful of jam onto a side plate and place it in the fridge for one minute. Remove it and push the jam away from you with your index finger. If the jam forms "wrinkles," then setting point has been reached. If there are no wrinkles, you need to boil your jam a little more. Use a kitchen timer when boiling jam, especially around the time when setting point will be reached soon, and add 5 minutes at a time until you get to setting point. THE PROBLEM is that if you boil your jam past setting point, it will never set! That is why testing for setting point often, and using the kitchen timer are both very important.

Answer 2

Clarification of Terms"Test for a gel" in the UK is the same as "test for setting point" in the US. Sometimes this is spelled "jel" or "jell".

A Little Preliminary Information

I shall not go much into the details of ingredient or mechanics in obtaining a set/gel other than to say that it usually requires pectin together with sugar and acid in the proper balance. Further details may be found in other articles elsewhere.

If your intended fruit (or fruit blend) is low in pectin, you will either need to add pectin or add a fruit high in pectin (e.g. apples, grapes, etc.).

Commercial pectin is available in both liquid and powdered forms. There is special type of pectin (low-methoxyl pectin activated by calcium) which does not rely upon that same balance which permits jams/jellies to be made with less, little, no sugar, or the use of other sweeteners (e.g. honey, Splenda®, etc.). Regardless of the type of added pectin, follow the recipe and instructions provided in the package. Keep in mind that a "full rolling boil" is one where it cannot be stirred down no matter how hard you stir.

As to the test itself

If you have a thermometer:

The gel point is 8°F/4°C above boiling point of water. Make a note of the boiling point of water with your thermometer before EACH jelly/jam making session; then test to the incremented temperature. THIS TEST IS ONLY GOOD IF pot is being stirred vigorously, thermometer tip is not resting of pan bottom, and there is no accumulation on thermometer tip.

If you do not have a thermometer:

Place several spoons into freezer before beginning jamming session. When you think it is close (changes to viscosity and color occur), remove pan from heat, place a small amount on one of the spoons (NOT by dipping the cold spoon) and place spoon back in freezer. After a moment or two, check to see if the spoon feels room temperature on the bottom: then, if so hold the spoon vertical. The setting point has been reached when the jam/jelly does not run; or, for a softer set, it moves very slowly. If not set, place the pan back on the heat and boil for another 5 minutes and test again. [from The Blue Chair Jam Cookbook by Rachel Saunders]

There are other methods of testing without a thermometer, but this one I have found easiest.

After is set/gel reached

Jar and process following safe and approved methods; OR place in refrigerator and consume within 3 weeks.