How to Make Watermelon Jam

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Watermelon Jam - Small-Scale Manufacture

Short Description

  • Problem: creating watermelon jam
  • Idea: Make it yourself
  • Difficulty: low
  • Price Range: low
  • Material Needeed: various cooking equipment
  • Geographic Area: worldwide
  • How Many people? 1 or more

Fully ripe watermelons that have a soft red flesh should be used for making jam. Watermelons contain little natural pectin so pectin has to be added to ensure the jam will have a good set. The yield of usable fruit from the whole fruit is approximately 43%.


Fruit juice

74% (starting recipe


55% before boiling)

Green ginger




Citric acid


In most countries, adding preservative to jam is not allowed. Only a residue of preservative is allowed in jam which has been made from fruit pulp which has been stored with chemical preservatives, (100ppm sulphur dioxide or 500ppm benzoic acid). Citric acid is not a preservative but is added to adjust the pH. Jams give a gel when there is the correct ratio of pectin to water and the pH is between 2.5-3.45 pH. The optimum pH to give a good gel is pH 3.0.


Wash whole fruit in clean water and discard any bad part of the fruit.

Remove the skin from the melon, cut the flesh into small pieces and remove the seeds. Mash the pieces into a pulp and strain through a muslin cloth.

Mix the pectin with a small portion of the sugar. This dry mixing of the pectin is important because pectin powder is very difficult to dissolve in water because it clumps together. If it is still a problem to dissolve, grind the sugar to a fine powder and then mix it with the pectin.

Mix the fruit juice, sugar, citric acid and green ginger in a stainless steel saucepan and start boiling the mixture. Near the end of the boiling process the pectin dry mix can be added. (The pectin should not be heated for longer than necessary because it will be broken down and then the jam will not set.) Jam should not be boiled for more than 12-15 minutes otherwise this can give rise to caramel flavours, over sweetness and discolouration, apart from being a waste of energy. By reducing the amount of water in the starting recipe the boiling time can be reduced.

The 'end point' is reached when the total soluble solids is up to 70% this is measured with a refractometer, (In most countries the legal minimum sugar levels in jam are 65% for jam in hermetically sealed containers and 68.5% for jam in non air tight containers.) 70% gives a safety factor. Jam with over 70% sugar can give problems during storage as sugar will recrystallise out into large chunks. The 'end point' is usually reached around 106-108°C (depending on barometric pressure and height above sea level).

When the jam has nearly reached this temperature samples are taken and tested on a refractometer, the sample must be cooled before being measured. This can be done be smearing it on a cold dry plate or saucepan lid. All implements used to take the sample must be dry, otherwise the reading will be reduced. It is important to stir the jam at all times during the heating process, otherwise burning will occur at the bottom of the saucepan, causing off flavours and discolouration. When the 'end point' has been reached, the jam should be filled into jars which have been cleaned and then steamed to sterilise them, and are still hot so that the jars do not crack. The jars should be filled as quickly as possible so that the jam is not heated for longer than necessary, or recontaminated because it has cooled down before being sealed in the jar.

The lip of the jar should be clean and dry (wipe with clean tissue paper) before placing the lid on it. The filled jars can be placed in water to cool down the jam so that it does no keep cooking in the jar, the water level should be kept below the lid of the jar. The gel formation takes place as the temperature comes down to around 55°C, if the jam is moved when the gel is forming the gel structure will be broken and the jam will not set.

Equipment list

Jars, omnia lids and labels

Omnia capper

Cooking facilities, gas ring, electric ring, etc

Stainless steel saucepan

Thermometer in protective jacket

Stainless steel cutting knife and spoon

Wooden spoon for stirring


Steam generator

Cutting board


Measuring cylinder



Mashing tool

References and further reading

Jam, Jellies and Marmalade, Practical Action Technical Brief

Passion Fruit Jam, Practical Action Technical Brief

Pineapple Jam, Practical Action Technical Brief

Strawberry Jam, Practical Action Technical Brief

Useful addresses and contacts

Note: This is a selective list of suppliers and does not imply endorsement by Practical Action and howtopedia.

Bellingham + Stanley Ltd.
Longfield Road, North Farm Industrial Estate
Tunbridge Wells, Kent, TN2 3EY
United Kingdom
Tel: +44 1892 500400
Fax: +44 1892 543115
Refractometers producers

Practical Action, The Schumacher Centre for Technology & Development
Bourton Hall, Bourton-on-Dunsmore, Rugby, Warwickshire CV23 9QZ, UK
Tel: +44 (0)1926 634400 Fax: +44(0)1926 634401 E-mail: Web:

Intermediate Technology Development Group Ltd Patron HRH -The Prince of Wales, KG, KT, GCB
Company Rag. No 871964. England Rag. Charity No 247257 VAT No 241 6164 92

References and further reading

This Howtopedia entry was derived from the Practical Action Technical Brief Energy from the Wind.
To look at the original document follow this link:

Useful addresses

Practical Action The Schumacher Centre for Technology & Development, Bourton on Dunsmore, RUGBY, CV23 9QZ, United Kingdom.
Tel.: +44 (0) 1926 634400, Fax: +44 (0) 1926 634401