Food Chemistry

852 18 Fruits and Fruit Products

marmalade is then poured into appropriate con-
tainers.

18.2.6.2 Jams

Jams are produced similarly to marmalades but
usually from one kind of fruit. They are thick-
ened by boiling and constant stirring of the whole
or sliced fresh or fresh stored raw material, or of
fruit pulp. Ordinary jams are also made from fruit
slurry. Boiling under a vacuum at 65–80◦Cof-
fers the advantage of preserving the aroma and
color. The disadvantages are the absence of su-
crose inversion and the low caramelization. These
reactions produce the characteristic taste of jams
boiled in an open kettle (T: 105◦C). Table 18.38
provides compositional data for some commer-
cial jams. The optimal pH of 3.0 required for
gelling is adjusted by the addition of lactic, cit-
ric or tartaric acid, if necessary.

18.2.6.3 Jellies

Jellies are gelatinous, spreadable preparations
made from the juice or aqueous extract of fresh
fruits by boiling down with sugar. The addition of
fruit pectin (0.5% as calcium pectate) and tartaric
acid or lactic acid (0.5%) is normal. In general,
the water content is 42%, and the sugar content
between 50% and 70%. The juice is boiled down
in open kettles or in vacuum kettles with sugar
(about half the weight of the fruit), pectin, if
necessary, and the substances mentioned above.

Table 18.38.Composition of various jams (average val-
ues in %)

Jam from Moisture Total Total Ash Dietary
sugar acida fiber

Strawberries 35. 058. 70 .89 0.23 0. 80
Apricots 36. 951. 31 .14 0.28 0. 60
Cherries 36. 657. 31 .26 0.28 0. 50
Blackberries 34. 258. 00 .37 0.24 1. 20
Raspberries 35. 954. 61 .03 0.23 1. 20
Bilberries 35. 155. 80 .60 0.22 0. 37 b
Plums/prunes 31. 159. 10 .42 0.24 0. 43 b

aSum of malic and citric acid.
bPectin as calcium pectate.

The scum is carefully skimmed off and the

mixture is boiled further until a moisture content

of about 42% is reached.

18.2.7 Plum Sauce (Damson Cheese)

Plum/prune sauce is produced by thickening

through boiling of fresh fruit pulps or fruit

slurries. The use of dried plums is also common.

Normally, the product has no added sugar,

but sweetened products or products with other

ingredients added are also produced. The soluble

solids have to be at least 60% by weight.

18.2.8 Fruit Juices

Fruit juices are usually obtained directly from

fruit by mechanical means, and also from juice

concentrates (cf. 18.2.10) by dilution with water.

The solid matter content is generally 5–20%. The

juices are consumed as such or are used as in-

termediary products, e. g., for the production of

syrups, jellies, lemonades, fruit juice liqueurs or

fruit candies. Fruit juice production is regulated

in most countries.

Juices from acidic fruits are usually sweetened

by adding sucrose, glucose or fructose. Juices

used for further processing usually contain chem-

ical preservatives to inhibit fermentation. Some

juices from berries and stone fruits, because of

their high acid content, are not suitable for dir-

ect consumption. Addition of sugar and subse-

quent dilution with water provides fruit nectars

or sweet musts (cf. 18.2.9). Since 1990, the per

capita consumption of fruit juice and fruit nectar

in Germany has been fairly constant at 40 l. In the

case of fruit juices, the products presented in Ta-

ble 18.39 are predominant.

Table 18.39.Per capita consumption of fruit juices in

Germany (2004)

Product Amount (l)

Apple juice 12. 8

Orange juice 8. 9

Multivitamin juice 3. 8

Grape juice 1. 3