Fruit and vegetable processing - Ch08 Fruit specific preservation technologies (cont.) (2024)

8.6 Fruit sugar preserves technology; jams,jellies, marmalade, fruit paste

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As a overall rule of thumb, asugar concentration of about 60% in finished or processed fruitproducts generally insures their preservation. Preservation isnot only determined by the osmotic pressure of sugar solutionsbut also by the water activity values in the liquid phase, whichcan be lowered by sugar addition; and by evaporation down to0.848 aw; this value however does not protect products from mouldand osmophile yeast attack.

Maximum saccharose concentrationthat can be achieved in the liquid phase of the product is67.89%; however higher total sugar quantities (up to 70-72%)found in products are explained by an increased reducing sugarsolubility resulting from saccharose inversion.

8.6.1 Jams

The preservation of fruit by jammaking is a familiar process carried out on a small scale byhousewives in many parts of the world. Factory jam making hasbecome a highly complex operation, where strict quality controlprocedures are employed to ensure a uniform product, but themanufacturing operations employed are in essence the same asthose employed in the house.

Fresh or pre-cooked fruit isboiled with a solution of cane or beet sugar until sufficientwater has been evaporated to give a mixture which will set to agel on cooling and which contains 32-34% water.

Gel formation is dependent on thepresence in the fruit of the carbohydrate pectin, which at a pHof 3.2 - 3.4 and in the presence of a high concentration ofsugar, has the property of forming a viscous semi-solid.

During jam boiling, allmicro-organisms are destroyed within the product, and if it isfilled hot into clean receptacles which are subsequently sealed,and then inverted so that the hot jam contacts the lid surface,spoilage by micro-organisms will not take place during storage.

The composition of jam made fromstone fruit and berry fruit is shown in Table 8.6.1. About 30% ofthe vitamin C present in fresh fruit is destroyed during thejam-making process, but that which remains in the finishedproduct is stable during storage.

The high moisture content of jam(equivalent to an equilibrium relative humidity of about 82%)makes it susceptible to mould damage once the receptacle has beenopened and exposed from some time to the air. No problems ofmicrobiological spoilage are likely to arise in the cannedproduct during storage.

TABLE 8.6.1 Composition of some fruit jams

Source: FAD/WFP, 1970

8.6.2 Marmalade

This sugar preserve is defined as"semisolid or gel-like product prepared from fruitingredients together with one or more sweetening ingredients andmay contains suitable food acids and food pectins; theingredients are concentrated by cooking to such a point that theTSS - Total Soluble Solids - of the finished marmalade is notbelow 65%".

8.6.3 Fruit paste

Fruit paste is a product obtainedin the same way as special non-gelified fruit marmalade but witha lower water content - about 25% TSS in fruit paste.

Lowering water content could beachieved by continuing boiling of the product or by drying theproduct by natural or artificial drying. An example of pastewithout sugar is the sun dried apricot or prune paste.

8.6.4 General procedure for the preparation of jams,jellies and marmalade

1. Boil the pulp or the juice (with water when necessary)
2. Add the pectin

* to the batch while stirring very vigorously
* Pectin which has previously been mixed with 5 times its weight in sugar taken from the recipe)

3. Boil for about 2 minutes to assure a complete dissolution
4. Add the sugar while keeping the batch boiling
5. Boil down quickly to desired Brix
6. Add the acid (usually citric acid) and remove the froth
7. Fill hot into the (previously cleaned) jars and close
8. Invert the jars for three minutes to pasteurize the cover

* Note: the pectin in solutioncan also be added at the end of the step (e) and has to beprepared as follows: use a strong blender. For one litre of wateradd slowly into the blender 25 g of pectin mixed with 100 g ofsugar taken from the recipe.

8.6.5 Basic recipes

The following recipes must beconsidered only as guidelines because the composition of thefruit can vary; also the taste of the consumers varies concerningthe consistency, the sweetness and acidity.

Before starting to make jam it isimportant to know the yield to settle the question on containers.The calculation is made as follows:

In these basic recipes it isassumed that the fruits are poor in pectin content.

Recipe 1. Fruit: sugar = 50:50;desired Brix in the finished product is 68.

Soluble Solids

Recipe 2. Fruit: sugar = 45:55;desired Brix in the finished product is 68.

Recipe 3. Fruit: sugar = 40:60;desired Brix in the finished product is 68.

Various factors must be takeninto account:

1. Size of the container: thequantity of pectin indicated in the recipes is valid forcontainers of 1 kg or less.

2. Finishing point: the quantityof pectin is given for a final Brix - Total Soluble Solids (TSS)of 68%.

If the final Brix is 66 increasethe pectin by 5%

" " is 65 " "" by 10%

is 64 " " " by 15%

" " is 62 " "" by 20%

" " is 60 " "" by 30%

3. Acidic taste. If the productis too acid, replace the citric acid by tartaric acid (63% of theamount of citric acid).

4. Formation of clots: If batchclots, it is probably due to the pH being too low or the or TSSbeing too high; correct accordingly.

5. Formation of liquid at thesurface: if liquid forms on the surface, it is probably due totoo low a pH or too low pectin content.

6. Crystallisation:

a) if liquid forms on thesurfaces, then the pH is too low; reduce the acid content;

b) if liquid does not form on thesurface, then TSS or pH is too high.

7. Formation of mould: the TSS isprobably below 68 deg. Brix. The filling may have been done at alow temperature. If the containers are large, wait until they arecold before closing.

8. Wrong batch: dilute the jamwith water to 30% TSS; cook briefly. Add this diluted jam to anew batch but in a ratio not exceeding 10%.

8.6.6 Processing of pineapple-papaya jam

The fruit should be prepared asper previous instructions.

For pineapples, the ends areremoved and discarded; the cores and outer parts of the fruitsare also removed. The fruit cylinders obtained are pulped througha special extractor (Fitzpatrick communiting machine) equippedwith a 0.40-in screen sieve; the pulp thus obtained is used formaking jam.

The papaya are prepared byhand-peeling the fruit; the fruit is then halved and the seedsremoved. It is then pulped in the communiting machine using a0.40-in screen sieve.

When ginger root is used asflavouring, it is peeled and macerated in a Kenwood blender to avery fine consistency.

A typical formula for apineapple-papaya jam (50:50 ratio) with ginger flavouring isgiven as follows:

Processing is carried out in thefollowing way:

The weighed fruit pulp is placedin a stainless steel steam-jacketed kettle and heated to about110°F under constant stirring.

When the product reaches thistemperature, the heat is turned off. The pectin (mixed in aboutten times its weight with some of the weighed sugar), is thenmixed into the fruit pulp, stirring constantly in order toprevent the pectin from clotting.

When the pectin has dissolved,the remainder of the sugar is added and dissolved completely inthe mixture. The heat is then turned on and the jam mixture isstirred constantly until it starts boiling vigorously. During theremainder of the cooking, the product is stirred occasionally.Near the finishing point (approximately 221° F), the citric acidand the ginger (if it is used) are also added.

Determination of the finishingpoint is done by removing samples at intervals, cooling, andreading the soluble solids by means of a refractometer equippedwith a Brix scale. After the jam reaches the proper Total SolubleSolids content, the heat is turned off and the surface scum/foamis removed.

The jam then is quickly put intoreceptacles which have been cleaned and sterilised with boilingin water for 30 minutes. The filling operation is done rapidly inorder to prevent the temperature of the jam from falling below190° F.

After filling, sterilised lids(boiled for 30 minutes in water) are placed on the receptaclesand they are then sealed.

After this operation thereceptacles are inverted for about 3 minutes to insure that thelids are sterilised. The receptacles are then placed upright. Atthis stage it is not necessary to do any further processing,therefore the receptacles are cooled in running cold water untilthey reach a temperature slightly above room temperature. Theyare then dried in air and labelled.

Evaluation of finished products.

During production at medium /large scale, it is recommended that quality controls be performedduring manufacturing.

After ten weeks of storage atroom temperature it is recommended that an examination offinished products be performed. The receptacles are opened andcontents carefully emptied on to enamel trays without disturbingthe formation of the jam.

The empty cans (if metal canswere used) are then inspected for signs of corrosion. Factorsother than flavour include colour, appearance, syrup separation,firmness and spreading quality. For flavour, jam is tested onpieces of bread. Samples are taken for measurement of pH (with aglass electrode pH meter) and Total Soluble Solids (with arefractometer equipped with a Brix scale).

This evaluation enables to have aquality check during product shelf life and to obtain data neededfor necessary improvements of future productions.

For pineapple-papaya jam,products made with 30% pineapple and 70% papaya with added gingerhas the highest score for flavour. The use of plain tin canscauses corrosion problems which is not the case when acidresistant lacquer cans are used.

8.6.7 Pineapple jam making

1. Boil 40 lb. of pulp and 12 lb. of water.
2. Add 225 g of pectin to the batch while stirring rapidly.
3. Boil for about 90 sec to assure complete dissolution.
4. Add 60 lb. of sugar gradually if possible in several portions, while keeping the batch boiling.
5. Boil down quickly to 69 deg. Brix (223 deg. F).
6. Take off steam, remove foam.
7. Add 300 cc citric acid solution 50%.
8. Fill hot (180 deg. F).
9. Invert receptacles for 3 minutes.

Check each batch for Brix 68-70deg.; acidity/pH = 3.2 +/- 0.2.

Evaluate: absence of defects;colour; flavour; consistency.

Various fruit:sugar ratios can bemanufactured; some basic recipes are as follows:

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