Watermelon Jelly
Practical Action
Mix the fruit juice, sugar, citric acid and green ginger in a stainless steel saucepan and start
boiling the mixture. Near the end of the boiling process the pectin dry mix can be added.
(The pectin should not be heated for longer than necessary because it will be broken down
and then the jelly will not set.) The jelly should not be boiled for more than 12-15 minutes
as this can give rise to caramel flavours, over sweetness and discolouration, apart from being
a waste of energy. By reducing the amount of water in the starting recipe the boiling time
can be reduced.
Boiling to reach the final sugar concentration
The aim of boiling is to reduce the water content of the mixture and concentrate the fruit and
sugar in as short a time as possible. The final Total Soluble Solids (TSS) content of a jelly (also
known as the “Degrees Brix” or “end-point of the jelly”) should be 65 to 68% (the TSS is a
measure of the amount of material that is soluble in water. It is expressed as a percentage -a
product with 100% soluble solids, has no water and one with 0% soluble solids is all water).
The correct sugar content is critical for proper gel formation and for preservation of the jelly.
If the final TSS of jelly is lower than 65-68%, the shelf life will be reduced. The jelly will
have a runny consistency and bacteria and moulds will be able to grow in the product. If the
TSS is higher than 68%, the jelly will be very stiff and the sugar might form crystals during
storage.
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 jelly will continue to cook and may become over-cooked. It is always
possible to cook the mixture 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 jelly 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 jelly for sale that a refractometer is necessary, to ensure consistency
between different batches of the jelly. When making jam or jelly 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 105°C).
When the jelly 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 jelly 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 jelly is poured in. If the jelly 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
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