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Jam and marmelade
Jams and marmelades are fruit jellies. The fruit has a shelf life of several months to more than a year due to addition of sugar, gelation and vacuum packaging. Once opened (release of the vacuum) the fruit jellies have a durability of a few weeks, at least when it is stored at cool temperatures (under 7°C). Besides jam and marmelade another fruitjelly is known, named confiture. In confiture hole fruits are used. For processing of jam the fruits are cut fine or even mashed. Marmelade consists of citric fruit most times the skins are used too. This gives a bitter sweet taste to the marmelade.
|Processing of traditional jam|
|Cutting and mashing|
|Processing of diet jam|
Processing of traditional jamFor the production of traditional jam four basic ingredients are needed: fruit (35-40%), sugar (55-65%), pectin (0.5%) and acid (0.3%). During the process a part of the water present in the fruit evaporates.
The fruit contains a small amount of pectin. This gives gelation. But the amount of natural gelatine is too small to gelate all the mass. Therefore extra pectin is needed. The sugar has, besides the function of giving taste, a function in gelating the mass.
CleaningFor the production of jam the fruit is cleaned at first. The unwanted parts are removed of the fruit. Than the fruit is washed with cold clean water to remove sand and mud.
Cutting and mashingAfter that the fruits are being cut (to a size of 0,1 to 0,5 cm3) and a part of fruit are being mashed. The puree with fruit parts is first cooked. Next a mixture of acid, sugar and pectin is added. To avoid lumps the pectin it is mixed with sugar at forehand. Cooking releases the 0,2-2% natural pectin, concentrates the mass and provides the solubility of sugar, acid and pectin. And helps to form a network between the pectin molecules and sugar.
GelatingThe gel network in jam can be formed between the pectin molecules, connected at several places. Pectin is a polymer of galacturonic acid molecules. It is partly estered with methanol. The amount of esters is responsible for the properties of the pectin. By the processing of traditional jam highly estered pectin is used, also called HM-pectin (High Methyl Estered pectin). This pectin forms a gel with the use of sugar and acid, an other name for this gel is sugar-acid-gel. The network holds water (with soluble matters as sugar) and fruit parts.
The pectin molecules can not make a gel network without sugar and acid. Due to the high water content of the fruit mass a hydratation layer (water molecules binded to the hydrogen bindings) is formed around the pectin molecules. Therefore the pectin molecules can not move freely and can not come close enough to each other to bind. Besides this, the free carboxyl groups are dissociated. H+ is loosened, a negative end is the result. This results in a a negative charge of the pectin molecules. A negative charge makes the molecules depart from each other. Binding is impossible.
Sugar binds water and takes water from the hydratation layer. The hydratation layer gets thinner and the pectin molecules can move more freely. But the negative charge is actually still very high, so the molecules keep pushing off each other.
When the acid is added the pH drops under 3.5. The positive hydrogen molecules bind the dissociated groups. The negative charge gets more neutral and the pectin molecules can approach each other so they can bind at several places.
CoolingThe binding between the pectin molecules exists of hydrogen bindings, between hydroxyl groups and between hydroxyl and non-estered carboxyl groups. The gel is a strong network that can keep fruit parts on its place. The network needs to be formed before the fruit parts starts floating. For a small part gelation takes place during the cooking process, but the utmost part of the gelation takes place during cooling down of the mass. For the correct distribution of the fruit a proper cooling process is required.
FillingAfter the cooking the hot jam is filled into glass pots. These pots need to be sterile, in spile of the high sugar content moulds and yeasts can grow. Moulds can not grow in a anaerobic medium. The pot should be vacuum closed to give mould growth no chance .
A vacuum in the pot can be reached easily by closing the pots in a normal way and turn the pots upside down for several minutes. The air can, while the jam is still warm, escape trough the pot and the lid. Because the jam is right behind the lid, air can not go into the pot.
After vacuum packaging the jam can be turned to its normal position and cooled to 20°C. Cooling of the jam pots can be done effective in streaming cold water. In this way gel forming will be obtained easily and the fruit has no possibility to float and is kept well divided.
Processing of diet jamThe production of jam requires a relative large amount of sugar. In diet jams this is not wanted. Without the large amount of sugar the HM-pectin network can not be formed. But the production of a network is possible with the use of Low Methyl Estered pectin (LM-pectin). With this pectin the network is based on a totally different principle.
The network of LM-pectin can be formed at a higher pH (higher then 3,5) and a low sugar content. But it requires cations like calcium ions. The calcium ions form a binding with the dissociated carboxyl groups and a calcium-pectinate-gel is formed.