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< prev - next > Food processing Preserves KnO 100272_Passion fruit jam (Printable PDF)
Passion fruit jam
Practical Action
The end-point of boiling is measured in different ways. The most accurate method is to use a
refractometer to measure the total sugar concentration. Remove the pan from the heat during
testing as the jam will continue to cook and may become over-cooked. It is always possible to
cook the jam a little bit more, but once it is over-cooked (and too thick) it cannot be reversed.
Cool the sample before it is measured by smearing it on a cold dry plate or saucepan lid. All
implements used to take the sample must be dry otherwise the reading will be reduced. It is
important to stir the jam at all times during heating, otherwise it may burn at the bottom of the
saucepan, causing off flavours and discoloration.
This method is not really suitable for home-use as a refractometer costs about US$ 150. It is
only when making jam for sale that a refractometer is necessary, to ensure consistency between
different batches of the jam. When making jam for home consumption, other methods can be
used to determine the end point: these include the drop test, the skin wrinkle test, or the use of a
jam thermometer to test the temperature (68% sugar corresponds to a jam temperature of
When the jam starts to thicken, it is important to test for the end point at frequent intervals.
Remember to remove the pan from the heat source while you test or it will continue to thicken
and may burn.
Filling into jars, cooling and labelling
Wash and sterilise the glass jars and lids by placing in a pan of water and boiling for 10 minutes.
Remove the jars from the water with a pair of tongs and stand upside down to drain. Do not dry
with a towel as this could contaminate the jars. If glass jars are not available, use plastic jars.
These cannot be sterilised with boiling water as they will melt. They should be thoroughly
cleaned in warm soapy water and rinsed with a weak solution of sodium metabisulphite.
Sterilising tablets (made of sodium metabisulphite) can be bought for this purpose.
Allow the jam to cool slightly (to about 80°C for glass jars and 60°C for plastic jars) and then
pour it into clean, sterilised jars. The jars should still be warm to prevent them from cracking
when the hot jam is poured in. If the jam is cooled too much it will be difficult to pour. Place the
clean lids on top and fasten. Invert the jars to form a seal. The filled jars can be placed in water
to cool down the jam so that it does not keep cooking in the jar. The water should not be too cold
or the glass may crack. Also, the water level must be kept below the lid of the jar. The gel starts
to form as the temperature of the jam reduces (about 55°C) and continues until it is cold. The
jars should not be moved or shaken while they are cooling or the gel will not form and the jam will
not set.
Jam that is hygienically prepared, boiled until it reaches the correct final total soluble solids
(68%) and which is packaged in sterilised glass jars can be stored for up to a year so long as it is
kept in a cool place away from direct sunlight. Jam that is packaged in plastic containers has a
shorter shelf life – up to 4 months.
Equipment list
Glass jars, Omnia lids and labels
Omnia capper
Cooking facilities, gas ring, electric ring, etc
Stainless steel saucepan
Thermometer in protective jacket
Stainless steel cutting knife and spoon
Wooden spoon for stirring
Cutting board
Liquidiser or mashing tool