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WATERMELON
JAM
SMALL-SCALE MANUFACTURE
Fully ripe watermelons that have a soft red flesh should be used for making jam. Watermelons
contain little natural pectin so pectin has to be added to ensure the jam will have a good set.
The yield of usable fruit from the whole fruit is approximately 43%.
Recipe
Fruit juice
74% (starting recipe
Sugar
55% before boiling)
Green ginger
0.8%
Pectin
0.4%
Citric acid
0.7%
In most countries, adding preservative to jam is not allowed. Only a residue of preservative is
allowed in jam which has been made from fruit pulp which has been stored with chemical
preservatives, (100ppm sulphur dioxide or 500ppm benzoic acid). Citric acid is not a
preservative, it is added to adjust the pH. Jams give a gel when there is the correct ratio of
pectin to water and the pH is between 2.5-3.45 pH. The optimum pH to give a good gel is pH
3.0.
Method
Wash whole fruit in clean water and discard any bad part of the fruit.
Remove the skin from the melon, cut the flesh into small pieces and remove the seeds. Mash
the pieces into a pulp and strain through a muslin cloth.
Mix the pectin with a small portion of the sugar. This dry mixing of the pectin is important
because pectin powder is very difficult to dissolve in water because it clumps together. If it is
still a problem to dissolve, grind the sugar to a fine powder and then mix it with the pectin.
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 jam will not set.) Jam should not be boiled for more than 12-15 minutes otherwise 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.
The 'end point' is reached when the total soluble solids is up to 70% this is measured with a
refractometer, (In most countries the legal minimum sugar levels in jam, are 65% for jam in
hermetically sealed containers, and 68.5% for jam in non air tight containers.) 70% gives a
safety factor. Jam with over 70% sugar can give problems during storage as sugar will
recrystallise out into large chunks. The 'end point' is usually reached around 106-108C
(depending on barometric pressure and height above sea level).
When the jam has nearly reached this temperature samples are taken and tested on a
refractometer, the sample must be cooled before being measured. This can be done be
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
the heating process, otherwise burning will occur at the bottom of the saucepan, causing off