Fully ripe watermelons that have a soft red flesh should be used for making jelly. The juice is extracted from the fruit and used to make a jelly, rather than a jam (jams contain pieces of fruit pulp whereas jellies are made from fruit juice). 
Watermelons contain little natural pectin so pectin has to be added to ensure the jelly will have a good set. Other fruits that are high in pectin, for example apple, rind of passion fruit, can be mixed with the watermelon juice if commercial pectin is not available. Watermelon juice is not very acidic (pH above 5.0) which is too high to make a good jam or jelly. Jams give a gel when there is the correct ratio of pectin to water and the pH is between 2.5 and 3.45 pH. The optimum pH to give a good gel is pH 3.0. Therefore citric acid has to be added to the recipe to reduce the pH and increase the acidity of the juice. The yield of usable fruit from the whole fruit is approximately 43%.
Recipe
(starting recipe before boiling)
Fruit juice: 74%
Sugar: 55%
Green ginger: 0.8%
Pectin: 0.4%
Citric acid: 0.7%
Method
1. Wash whole fruit in clean water and discard any bad part of the fruit.
2. 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.
3. 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.
4. 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 jelly will not set.) The jelly should not be boiled for more than 12-15 minutes as 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.
Boiling to reach the final sugar concentration
The aim of boiling is to reduce the water content of the mixture and concentrate the fruit and sugar in as short a time as possible. The final Total Soluble Solids (TSS) content of a jelly (also known as the “Degrees Brix” or “end-point of the jelly”) should be 65 to 68% (the TSS is a measure of the amount of material that is soluble in water. It is expressed as a percentage -a product with 100% soluble solids, has no water and one with 0% soluble solids is all water).
The correct sugar content is critical for proper gel formation and for preservation of the jelly. If the final TSS of jelly is lower than 65-68%, the shelf life will be reduced. The jelly will have a runny consistency and bacteria and moulds will be able to grow in the product. If the TSS is higher than 68%, the jelly will be very stiff and the sugar might form crystals during storage.
The end-point of boiling is measured in different ways. The most accurate method is to use a refractometer to measure the total sugar concentration. Remove the pan from the heat during testing as the jelly will continue to cook and may become over-cooked. It is always possible to cook the mixture a little bit more, but once it is over-cooked (and too thick) it cannot be reversed.
Cool the sample before it is measured by 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 jelly at all times during heating, otherwise it may burn at the bottom of the saucepan, causing off flavours and discoloration.
This method is not really suitable for home-use as a refractometer costs about US$ 150. It is only when making jelly for sale that a refractometer is necessary, to ensure consistency between different batches of the jelly. When making jam or jelly for home consumption, other methods can be used to determine the end point: these include the drop test, the skin wrinkle test, or the use of a jam thermometer to test the temperature (68% sugar corresponds to a jam temperature of 105°C).
When the jelly starts to thicken, it is important to test for the end point at frequent intervals. Remember to remove the pan from the heat source while you test or it will continue to thicken and may burn.
Filling into jars, cooling and labelling
Wash and sterilise the glass jars and lids by placing in a pan of water and boiling for 10 minutes. Remove the jars from the water with a pair of tongs and stand upside down to drain. Do not dry with a towel as this could contaminate the jars.
If glass jars are not available, use plastic jars. These cannot be sterilised with boiling water as they will melt. They should be thoroughly cleaned in warm soapy water and rinsed with a weak solution of sodium metabisulphite. Sterilising tablets (made of sodium metabisulphite) can be bought for this purpose.
Allow the jelly to cool slightly (to about 80°C for glass jars and 60°C for plastic jars) and then pour it into clean, sterilised jars. The jars should still be warm to prevent them from cracking when the hot jelly is poured in. If the jelly is cooled too much it will be difficult to pour. Place the clean lids on top and fasten. Invert the jars to form a seal. The filled jars can be placed in water to cool down the jelly so that it does not keep cooking in the jar. The water should not be too cold or the glass may crack. Also, the water level must be kept below the lid of the jar. The gel starts to form as the temperature of the jelly reduces (about 55°C) and continues until it is cold. The jars should not be moved or shaken while they are cooling or the gel will not form and the jelly will not set.
Storage
Jam and jelly that is hygienically prepared, boiled until it reaches the correct final total soluble solids (68%) and which is packaged in sterilised glass jars can be stored for up to a year so long as it is kept in a cool place away from direct sunlight. Jam or jelly that is packaged in plastic containers has a shorter shelf life – up to 4 months.
Equipment list
Glass 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
Refractometer
Cutting board
Scales
Liquidiser or mashing tool
Watermelon Jelly
makes 2 1/2 to 2 3/4 pints
6 cups pureed watermelon (remove any seeds prior to pureeing)
5 cups white sugar
4 6 tablespoons bottled lemon juice (due to concerns about acidity, I’ve increased the amount of lemon juice called for in this recipe)
1 packet powdered pectin
Combine watermelon puree, sugar and lemon juice in a large, non-reactive pot. Bring to a boil and let cook until the temperature of the nascent jelly reaches 220 degrees. Add the powdered pectin and boil for another five minutes.
Remove from the heat and pour into prepared jars. Wipe rims, apply lids and screw on bands. Process in a boiling water canner for 10 minutes.
When time is up, remove from canner and let jars cool. When they’re cool enough to handle, remove rings and test seals. You can eat immediately or store unopened jars in a cool, dark place for up to a year.
*Note: This jelly can take up to one week to set. Please give it time. ~ Recipe found at food in jars
Sources: 1. Practical Action
The Schumacher Centre for Technology and Development
Bourton-on-Dunsmore
Rugby, Warwickshire, CV23 9QZ
United Kingdom
Tel: +44 (0)1926 634400
Fax: +44 (0)1926 634401
E-mail: inforserv@practicalaction.org.uk
Website: http://practicalaction.org/practicalanswers/
2. foodinjars.com
Photo: etsy.com
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