The technical brief on jams and marmalade production outlines the principles of jam boiling.
Ideally a heavy based stainless steel pan or double bottomed jam pan will be available for boiling
the mixture. The other desirable pieces of equipment are a wooden stirrer, jam thermometer and
possibly a refractometer (figure 3) for testing the total soluble solids and determining the end
point of the boiling process.
1. Place the lime juice, bicarbonate and half the sugar in the pan, heat slowly to dissolve
the sugar and then bring to the boil. Boil for 3 - 5 minutes with steady stirring (it is
impossible to state boiling times exactly, as this depends on the heat source etc).
2. Add the remaining half of the sugar, peel, pectin and green colour and continue boiling
until the required sugar level (68%) is reached (as measured either by refractometer, jam
boiling thermometer or skill of the producer).
3. Filling and capping
Hot fill the finished preserve into
clean, dry jars and cap
immediately. Care is needed not to
fill too hot or too cold, the ideal
range being 82-85°C. Filling whilst
too hot can result in drops of steam
condensing on the inside of the lid,
falling back onto the surface of the
product and diluting it to below
68% sugar solids (so that moulds
and yeasts can grow). Too cold
filling carries the danger of
microbiological contamination from
the jar etc.
Cap the jars quickly using either
screw type or 'Omnia' type push-on
lids. When the jars have cooled
and a vacuum has formed (about
Figure 3: Refractometer
50°C) rinse them in a bath of clean
chlorinated water - one tablespoon
of bleach per 4.5 litres of water.
Dry the jars and label (see the technical brief on labelling for more details of the legal
requirements for food labels).
If properly preserved and packaged in glass, marmalade can be stored for up to one
year away from direct sunlight. If it is packaged in plastic bottles, it can only be
stored for about 4-6 months.
pH meter (optional)
Stainless steel pan
Gas ring or other heat source