the fruit equals that of the syrup, they will both have the same density. This will be at the point where
the fruit will neither float nor sink in the syrup.
This can be worked out by preparing a syrup slightly too concentrated in sugar, in which the fruits float,
and adding water slowly to dilute the syrup until the point is reached at which the fruits stop floating.
Like dried vegetables, dried fruits should be cooked in totally pure water, in order to allow complete
hydration of the fruit. If sugar is desired, it should be added afterwards, or else it will prevent the fruit
from completely hydrating.
Jam is a made from heating a mixture of sugar, fruit with a little water. On cooling, this mixture will
solidify because pectin molecules will be detached from the fruit cell walls during heating, and will to
re-associate to form a 3 dimensional network. This mesh traps liquids, causing the jam to set as it
cools and a “gel” is formed.
The ability a jam has to set or gel depends on the quantity of pectin in the mixture. Acidity greatly
affects the linking of pectin molecules and thus gelling ability. Often, if fruits are not sufficiently acidic,
extra acid must be added to neutralise the negative acid groups on the pectin molecules, preventing
their repulsion, and this favouring their association and gel forming ability. The degree of esterification
of the pectin molecule affects the gelling properties of pectin, explaining why some fruits gel well and
others do not. For example, citrus and apple pectins are very good gelifiants, but beetroot pectin
however doesn’t gel.
To make a well set jam, pectin extraction should be maximised. This can be done in three ways :
· firstly, fruits high in pectin should be used. Certain fruits do not contain enough pectin to make a
good jam (rhubarb, apricots, peaches, strawberry) whereas other fruits are abundant in pectin
(oranges, apples, grapes, most berries). Fruits low in pectin are often combined with those
high in pectin, or else purified pectin can be added. Purified pectin an be used as a gelling