What’s wrong with my jam? Common mistakes and how to fix them

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  • Making jam at home can be very rewarding, but unfortunately the results may not always be perfect. Is your homemade jam too runny, or thick? We've put together some common mistakes and tips on how to avoid them.

    Jam is a wonderful way to preserve a glut of fruit and always fills your home with a glorious sweet aroma. If properly jarred and stored jam will last for ages. A jar of homemade jam makes for a lovely personal edible gift, if you can bear to part with it that is! However sometimes jam goes wrong. We’ve all been there, with a sticky mess congealed in the bottom of our largest pan. This is how we fix, or when we ditch our jammy mistakes.

    Why is my jam too runny?

    This is a very common mishap, and can occur for a couple of reasons. It may because there is not enough pectin and acid in the mixture. Or it may be because the temperature of 104C was not reached when cooking.

    While hot the jam will seem runny, but be patient, as jam takes a while to cool and set. Samuel Goldsmiths, Woman & Home Food Editor has a nifty trick to test if the jam will set firm. He says “I always put teaspoons in the freezer and then dip in the jam when I think it’s done. If the jam sets on the spoon when I put the spoon in and out quickly then I know the jam will set.” Jam that was not heated to 104C-105C will not set. In this is the case heat the jam again. Use a jam thermometer to check when it reaches temperature.

    However if the jam has been heated sufficiently, but still did not set, then it requires more pectin and acid.

    Some fruits are naturally high in pectin and acid. Fruits rich in pectin and acid such as apple, blackcurrants, gooseberries and red currants will set a jam firm with little additions. However other fruits with lower pectin content will require a helping hand. Raspberries, plums and apricots all fit into this category. Strawberries, melon and cherries do not contain any pectin. Therefore when making jam with these fruits it is essential to add pectin in order for the jam to set.

    TOP TIP: The easiest way to add both acid and pectin to jam is simply by adding lemon juice. Lemon juice contains both in abundance. The ratio we use when making jam is adding 1tbsp of lemon juice to every 1kg of fruit. Woman & Home Food Writer, Keiron George, advises “If you’re having trouble with setting your jam, bring it to the boil again, adding the rind of a lemon for some extra pectin”.

    Why is my jam too thick?

    Fruits that are high in pectin such as apple, citrus fruits and pear will produce thick jams. The standard ratio in jam is equal measures of sugar to fruit. However, you may notice in recipes for jams made using high pectin fruits contain more sugar. This is to give the jam a better, less firm, consistency.

    It’s too late to add more sugar if the jam has already set and cooled. In this case it can be thinned out by mixing in a little sugar syrup. If the jam is very firm and has a rubbery consistence, gently warm it while adding the syrup. But do not bring it to the boil again.

    A sugar syrup is a mixture of equal amounts of water and sugar. The sugar is dissolved in the water by heating them together and stirring. Mixing in sugar syrup should give the jam a better cinsistency. However it may also affect the shelf life. Therefore we would recommend that you only add sugar to one jar at a time and store it in the fridge.

    Why does jam taste bitter?

    Your jam may taste bitter because it’s over-cooked. Sometimes overcooked jam can be good thing, as it has a nice caramel flavour that will work well used in desserts. However if it’s really overcooked the sugar will give it a bitter burnt taste. Sadly if the jam is burnt it’s beyond saving.

    Why does my jam have white lumps in it?

    If you’ve spotted white lumps in your jam, it is most likely sugar crystals. When making jam try to limit the amount of stirring you do after adding the sugar. Sometimes mixing the sugar will encourage it to crystallise. Although it might not look perfect, there’s no need to worry about these white lumps – it will still taste ok.

    Why is my jam cloudy?

    Despite your best efforts, sometimes jam will just go cloudy. This may have been caused by the sugar, which may have crystallised during the cooking process. Another common cause may be the ‘scum’ which has surfaced to the top of the jam during cooking – it’s very important you skim this off while cooking the jam to avoid this cloudy effect. There is nothing you can do to fix this in retrospect. However it’s not a deal breaker, and the jam should still taste equally as delicious.

    TOP TIP: When making jam it’s best to skim off the scum using a slotted spoon while the jam is cooking. Or, to stop a scum forming add 1/2 tbsp of glycerine (for every 1kg of fruit) once the sugar has dissolved.

    Plum Jam

    Why has my jam gone mouldy?

    Sometimes jam goes mouldy. It may be because bacteria was trapped in the jar, or it may because the recipe did not contain a sufficient amount of sugar to preserve the fruit. It’s imperative when making jam that the jars are sterile. If they contain bacteria this will cause mould. There are a number of methods for serialising jam jars. See this guide on how to sterilise jars on our sister site, GoodtoKnow.

    Pour hot jam into the jars and put a piece of wax paper neatly on top of the jam, wax side down, ensuring there are not air bubbles. Allow the jam to cool before firmly screwing on airtight lids. It’s safest not to risk eating jam which has started growing mould.

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