Add approximately equal weight of sugar to weight of fruit and
if required, citric acid to obtain pH 3.0-3.3, (pH meter optional)
and any extra pectin required. For marmalade, add thinly
sliced citrus peels that have been boiled in 60% sugar syrup
for 15 minutes and stored for at least 24 hours before use.
Check thickness of peels. A preservative, such as 1.8%
sodium benzoate is optional.