Glossary and Abbreviations - Unido

Sweet potato jam
Sweet potato jam is made from pulped root with added sugar, pectin and citric acid. The
combination of high acidity (pH around 3.0) and high sugar content (68-72%), prevents mould
growth after opening the jar. There are two important points to remember when making jam:
1) There must be the correct proportions of pulp, sugar, acid and pectin in order to form a
good gel.
2) Water must be boiled off quickly to concentrate the mixture before it darkens. A stainless
steel pan and a gas burner can be used, and the mixture should be constantly stirred to
prevent it burning onto the base of the pan, particularly towards the end of boiling when it
thickens.
Methods to test for the correct point to stop boiling are described in Section 6.1, and a
summary of common faults in jam making is shown in Table 4.10.
Pectin is available commercially as either a powder or a liquid concentrate. It is stable if
stored in cool, dry place and it will only lose about 2% of its gelling power per year.
Powdered pectin is added to the sweet potato pulp at 3-6g per kg of final product, but it
should first be mixed with about five times its weight of sugar to prevent lumps forming when
it is added to the pulp. Liquid concentrate can be added directly to the pulp. There are a
large number of different types of pectin, such as ‘rapid set’ and ‘slow set’ and it is
necessary to specify carefully the type required when ordering pectin from a supplier.
Jam should be hot filled (at around 85 o C) into glass jars and sealed with a new lid. If the
temperature is too high, steam condenses to water on the inside of the lid and dilutes sugar at
the surface of the jam, which can cause mould growth. If the temperature is too low, the jam
thickens and is difficult to pour into containers. Jars should be filled to approximately 9/10 ths full,
to help a vacuum to form in the space above the product as it cools. The problems of obtaining
glass jars in Uganda have led some producers to use polythene tubs, but these are not easy to
hot-fill because they melt, and the lid seals are often not good enough to prevent product
leaking out and attracting insects. Polypropylene pots are more suitable, especially if a heat
sealed foil lid is used.
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