Fructose is the sweetest of all naturally occurring sugars. It is found in fruits, vegetables,
and honey. This monosaccharide is a reducing sugar, capable of combining
with amino acids to produce desirable ‘brown’ flavours and colours in products like
baked goods.
The clumping tendency is easily overcome when some dry, readily soluble substance
like sugar is mixed with the pectin to serve as a spacer. Usually four to five
times as much sugar as pectin is used.
Liquid spacing agents such as glucose, sucrose syrup, or honey may be used to
make a slurry so that when water is added, with stirring, the pectin goes into solution
without clumping.
In a great many instances, the cause for the failure of a batch to set properly is improper or
incomplete dissolving of the pectin. Sufficient water or fruit juice (to which no sugar has
been added) should be used so that there are at least 15 L for every ½ kg of pectin. The
pectin should be mixed with only four to five parts of sugar so that when it is dissolved in
the water or fruit juice, it will not produce a heavy sugar syrup. It should be stirred into the
warm liquid to prevent any lumping and then brought to a very vigorous boil to make sure
that all the pectin is in solution before any additional sugar is added to the batch. If ½ kg
of pectin is being dispersed in sufficient water to make 12–15 L of solution, the agitation
should be of high speed type to prevent the forming of lumps while the pectin is being
slowly sifted into the solution. In this degree of concentration, the batch should be run at
least 15min before the pectin can be considered completely in solution, or if it is being
dissolved in a steam-jacketed kettle, the final solution can be brought to a vigorous boil,
which would ensure complete solution. (See section on Dissolving Pectin.)
2. The Brix of the finished product should be checked—if the final cook is below the recommended
temperature of 105°C (221°F) for a 65°Brix product, the result will be a weakness in the texture
of the gel. In trouble of this type, a refractometer, with a direct-reading sugar scale, is invaluable
because instantaneous and easy readings of the soluble solids can be obtained directly.
3. The pH of the batch should be tested. The pH has a significant effect on pectin gel formation.
Even though sugar and pectin are present in correct amounts, no gel will form until acidity has
been adjusted below a limiting pH, which is near 3.50. A shift of 0.05 in the range of 3.3–3.5
can sometimes make the difference between success or failure for a jelly maker. Fruit jellies of
pH 3.3–3.5 may require several weeks to reach maximum firmness. A small portion of the jelly
or jam should be checked on the pH meter to determine if the pH value is higher, above 3.5, than
that recommended where maximum gel strength will be obtained. If so, there is the possibility
that not enough acid has been added or the acid has been left out altogether. Another possibility
is that the fruit juice or the fruit may contain an abnormally high amount of buffer salts. These
salts will tend to reduce the effective acidity in the batch and may completely prevent setting.
4. Failure to add a sufficient amount of pectin. Often, an insufficient amount of pectin was
added, or through an oversight, the pectin may have been left completely out of the batch. If
the pH and Brix of the finished product are within their respective satisfactory ranges, it may
be entirely possible that not enough pectin was added at the beginning of the cook.
9.13.2 Excessive floating of fruit in the jam
Fruit can normally be prevented from floating by using rapid-set pectin during the
cooking of open-kettle jams and cooling the batch to approximately 88°C (190 °F)
before filling it. In the case of vacuum cooking, a helpful procedure is to break the
vacuum at the end of the cook to force the syrup into the partially evacuated centres
of the berries, increasing the weight of the berries to a point where they will not float.
However, there are some instances, such as in the manufacturing of cherry jams,
in which it is very difficult to prevent floating by either of these means, although they
336 A Complete Course in Canning and Related Processes
both are a great help in overcoming this tendency to float. The reason for the floating
of the cherries in the finished jam is that during the cooking process, the syrup around
the fruit concentrates to a greater specific gravity than the juice and syrup inside the
fruit. Therefore, the fruit is lighter than the syrup.
One means of overcoming this is to cook the batch a little beyond the desired Brix
(probably up to 71°Brix) and then reduce the syrup concentration by the addition of
water. By this process, the concentration of the syrup, both inside and outside the fruit,
is raised above the point needed; when the concentration is cut back with water, only
the syrup on the outside is reduced.