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< prev - next > Food processing Preserves KnO 100272_Passion fruit jam (Printable PDF)
Passion fruit jam
Practical Action
In most countries, preservative cannot be added to the jam. 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). Sodium bicarbonate is not a
preservative. It is added to adjust the pH of the jam if the juice is too acidic. Jams give a gel
when there is the correct ratio of pectin to water and the pH is between 2.5-3.45pH. The
optimum pH to give a good gel is pH 3.0. Therefore, sodium bicarbonate is generally added to
passion fruit juice to decrease the acidity.
Wash whole fruits in clean water and discard any bad fruits.
Cut fruits in half with a stainless steel knife and scoop out the pulp with a stainless steel spoon.
Stainless steel equipment is preferred for fruit as it does not stain the flesh and does not react
with the acidity of the juice. If stainless steel is not available, make sure the knives and spoons
are not rusted. Use a plastic spoon to scoop out the flesh.
Extract the juice from the pulp by liquidising the pulp at a very low speed for about a minute. It
is important to use a low speed to prevent the seeds from chipping. Chipped seeds appear as
black specks in the jam. They are very difficult to remove and give the product a bad appearance.
Tip the contents into a muslin cloth and squeeze out the juice leaving the seeds behind. This
method will give a yield of raw juice from whole fruit of between 30 to 35%.
Measure the amount of juice extracted and use this to calculate how much skin pulp is required.
Skin pulp is added to the jam as it contains natural pectin and so saves adding artificial pectin
which is expensive.
To make skin pulp take the same quantity of skins, as skin pulp required. Boil the skins for
approximately 30 minutes, until the flesh of the skin is soft and translucent. Then remove the
skins from the water and scoop out the flesh from the outer cuticle. Liquidise this softened flesh
with water (2 parts softened flesh to 1 part water) until it forms a smooth cream. Use the water in
which the skins were boiled as this will contain pectin washed out during the boiling. Squeeze
the mixture through a muslin cloth to remove hard pieces of pith.
Mix the raw juice with sodium bicarbonate (NaHCO3) before boiling (if the NaHCO3 is added
during boiling the jam will bubble-up over the top of the saucepan). Add the sugar and water and
heat gently at first to ensure the sugar has dissolved. Then boil rapidly to evaporate the water and
continue until the jam thickens. Keep stirring during boiling to make sure the jam does not stick
to the base of the pan. Jam 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 jam (also known as the
“Degrees Brix” or “end-point of the jam”) 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 jam or
jelly. If the final TSS of jam is lower than 65-68% the shelf life will be reduced. The jam 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 jam will be very stiff and the sugar might start to form crystals in the