How to make the perfect Jam

Jam must contain enough acid and pectin [a natural gum-like substance present in fruit in varying proportions] in order to set properly and sufficient sugar to preserve it.

For best results:

•   Cook small amounts at a time, as a guide avoid using more than 2kg of fruit for any recipe.  Shorter cooking time gives better results in flavour, texture and appearance.
•    If you wash fruit, dry it well and use promptly because it will deteriorate on standing.
•    Cook fruit very slowly at first over a low heat to extract the maximum amount of juice and pectin.  Stir frequently until very tender but do not overcook.
•    Make sure fruit skins are completely softened [can squish between two fingers] before adding sugar as it can have a hardening effect. Especially important when making marmalades.
•    Dissolve sugar in the liquid before it begins to boil or it can crystallize.  Stir to ensure all dissolved.
•    Do no stir jam once boiling, but use a wooden spoon to check it is not sticking on the base of the pan. Stirring lowers the temperature and delays setting point being reached.
•    It is wasteful to remove scum too often.  Do it at the beginning and at the end.
•    Do not move newly filled jars until they are cool and have set completely.  Setting can sometimes take a day.


Use slightly under ripe or just ripe fruit.  Over ripe fruit has less pectin and may ferment in the jars.  Freezing can also reduce the pectin content.   Use green/cooking apples when combining with other fruits.  Apples that have been in cold storage will not give as good results.


Forms a gel when boiled with sugar and acid, and on cooling sets to give jam its characteristic soft, spreading consistency.    Pectin is found in the skin, flesh and seeds of fruit to varying degrees.  Some fruits are naturally richer in pectin and acid while others are low or have none at all and need the addition of pectin containing fruit.    Testing for pectin – see Sugar below.


Helps to extract pectin from fruit, improves the flavour and colour of a jam and helps prevent crystallization.  If low, acid can be supplemented with the addition of lemon juice or by combining fruits together.

Lemon/ lime juice adds pectin and acid, prevents fruit from turning brown and enhances flavour and colour.   Citric acid is sold as fine white crystals and can be used instead of lemon juice in preserves.

Fruit with good balance of pectin/acid:

:Crab apples
:Cooking/sour apples
:Currants: Red/white/Black
:Lemons/limes/ grapefruit/ sour oranges
:Sour cherries
:Sour damsons
:Sour gooseberries
:Sour plums

Fruit high in pectin/ low in acid:

: Eating apples
: Sweet guavas
: Sweet quinces

Add 2 tablespoons of lemon juice to each 1kg of fruit to increase acid content

Fruit with low pectin/ high acid:

: Apricots
: Blackberries [early]
: Rhubarb
: sour peaches
: Sweet citrus fruit eg nectarines

Add 2 tablespoons of lemon juice to each 1kg of fruit to increase pectin content.

Fruit with low pectin/ low acid:

: Most berries inc late blackberries
: Pears
: Sweet peaches
: Sweet cherries
: Melons
: Sweet plums
: Strawberries

Not suitable without additional fruits/ juices to increase acid/ pectin content


Is not just a sweetener but is vital to its setting and keeping qualities.  Too little and a jam will ferment; too much and it will crystallise.  When used in high concentrations, sugar is a preservative which inhibits the development and growth of micro organisms.
To reach a high enough concentration,  ¾ to 1 cup [250 gms] of sugar must be used per 1 cup of fruit mixture [ie sugar content needs to be between 60%-70%  of total weight].
Guide to quantities:
Higher pectin fruits – 1 cup of sugar to 1 cup of fruit liquid.
Lower pectin fruits – ¾ cup of sugar to 1 cup of fruit liquid.

Testing for pectin:

Place 1 teaspoon of strained fruit liquid in a glass; add 3 teaspoons of methylated spirits and stir the mixture gently with a teaspoon.
1]  mixture forms a  fairly solid single jelly like clot – the fruit mixture is high in pectin.  Use 1 cup of sugar per cup of fruit mixture
2]  mixture forms 2-6  clots of jelly – moderate in pectin.  Use ¾ cup of sugar to 1 cup of fruit mixture
3]  no clots or a mass of tiny clots – very little pectin so needs additional pectin added.  Add 2 tablespoons of strained lemon juice to each kg of fruit used; add this after the sugar has been added.   Depending on which fruit used then choose whether to add a cup or ¾ cup of sugar.  [If the fruit mixture looks “watery”, you can try simmering the mixture longer to concentrate the juice by evaporation and test again.  However be careful not to overcook the fruit]


Recipes vary depending on fruit used and the percentage of whole fruit to liquid mixture. 

•    Soft juicy fruits need little water [or no water if wanting thick fruit jam] added to the pan and a short cooking time.
•    Harder fruits need just enough water to prevent the fruit from burning and a longer cooking time, perhaps 30-45 mins.
•    Citrus fruit for marmalades use more water, at least covered, as they take longer cooking and by definition, are softened fruit skin suspended in a jelly like preserve.

Cooking times vary greatly between recipes depending on the size of the pan, the fruit used, the time of year, if the fruit is in season, etc.  Therefore, it is necessary to test for setting point sometimes up to 10 mins before the recipe’s stated time, to make sure it is not ready to be bottled.  If it is looking thick and syrupy then it is worth testing.

Testing for setting:

Various recipe books give different methods.  The following is a combination:

•    Dip a wooden/melamine spoon in the mixture; raise the spoon up high above and parallel to the mixture; and tilt the bowl of the spoon towards you. As the mixture cooks and thickens, the drops will fall more heavily from the spoon. When it is ready, two or three drops will roll down the edge of the spoon and join together in a heavy mass/sheet. The jam is nearing it setting point.
•   When this happens, remove the pan from the heat to stop cooking.  Drop a teaspoon of mixture onto a saucer which has been chilling in the freezer, and return to the freezer for about 30 seconds or until the jam has cooled to room temperature.
•    Jam with pieces of fruit in it [marmalades/ conserves] should have formed a skin which wrinkles when you push it with a finger
•    Jam which is pulpy in texture should be of a spreadable consistency
• If this does not happen, return the pan to the heat and after a few minutes, repeat the testing with a second cold saucer.  Continue till it jells.


•    Jams made of pulpy fruit should be bottled and sealed immediately.
•    Jams containing pieces of fruit need to stand for 5-10 minutes [depending on the size and type of fruit used] before bottling and sealing. This allows the fruit to be suspended evenly in the mixture. Marmalades often need the full 10 minutes.
•    Do not leave jams too long as they will begin to set in the pan.  If this happens, gently heat the mixture till it returns to more of a liquid. Do not reheat for more than a minute or two.

Common problems:

Jam has not set/ too runny:
due to an imbalance of pectin and acid; or insufficient evaporation in the cooking process.  Action:  looks rather watery – return jam to the pan, bring to the boil again for a few minutes and retest for setting.  Otherwise lemon juice can added and jam re-boiled until it will jell when tested.

Jam has darkened in colour and has a caramel taste: This happens when sugar is over cooked.  Even if not set, it cannot be re-boiled as above.

Tough fruit: the fruit was not cooked long enough before the sugar was added.  Sugar hardens fruit and it does not soften any further.

Fruit floats to the top: the fruit was not cooked long enough or did not stand long enough when bottled.

Crystallization: too much sugar was added to the fruit, and it was not dissolved before boiling.

Fermentation: mushy, overripe, bruised or damaged fruit was used in the cooking process, or not enough sugar was added to the fruit mixture.

Elizabeth Highton – March 2011

5 thoughts on “How to make the perfect Jam

  1. I found this site very useful, simple easy to follow instructions, straight to the point with no flowery language or chit chat.



    1. Hi the reason why the am crystalised in the first place is because the sugar wasn’t fully dissolved before boiling. It is unlikely that anything can be done now as I doubt re-boiling will solve the problem, but it may be worth trying a small batch to see if this works.


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