Read Part 1- Introduction to Jam, Jelly and Marmalade Production
A. Lime Marmalade
- 1 liter lime juice
- 20g sodium bicarbonate
- 3kg sugar
- 1200g 5SAG pectin (made from 40g pectin, 200g sugar and 960ml water)
- few drops green food color
- 200g sugared lime peel shreds
- Marmalade is made according to the basic jam/marmalade method. However, there are a few quality assurance points that must be observed:
- Limes have a very high level of acidity (pH 2.7- 2.9) which means that they need to be treated differently to most other fruits.
- Fruit preserves need a pH of between 3.0 and 3.3 to enable the pectin to make a strong gel. Therefore the pH of lime juice has to be increased by adding sodium bicarbonate (baking powder).
- The amount of sodium bicarbonate added varies according to the variety and acidity of the lime. The acidity is measured using a pH meter if one is available. If one is not available, then a series of tests must be carried out to find the correct amount of sodium bicarbonate to add to make a good gel. About 20g sodium bicarbonate per litre of juice is a good starting point.
- One of the problems of making marmalade is to ensure that the peel pieces are evenly distributed throughout the gel, not floating at the top. This is achieved by soaking the peel in sugar so that it has the same density as the gel.
- After squeezing out the juice, the lime peel must be shredded into very thin slices about 1-2.5cm long. The shreds are saturated in sugar.
- The shredded peel is mixed with sugar (1kg peel and 1kg sugar) and left in a sealed container for one week, stirring occasionally. After this time, the shreds will be floating in a dense syrup. Sodium metabisulphate (1g per kg peel) can be added to prevent the growth of mould and yeast.
- Extraction of the lime juice is time consuming and tedious. Use of a small juicer is recommended. The juice is very acidic and therefore should not be collected in metallic containers. Only use food-grade plastic, stainless steel or wooden utensils. The juice must be filtered or strained to remove any pulp.
- Fruit juice can be preserved for later use by adding 3g sodium metabisulphate per liter of juice and storing in a sealed container.
- The lime juice, bicarbonate and half the sugar are placed in the pan, brought to the boil and boiled for 3 – 5 minutes with steady stirring (it is impossible to state boiling times exactly, as this depends on the heat source etc).
- The remaining half of the sugar, peel, pectin and green color are added and boiling continued until the required sugar level (68%) is reached (as measured either by refractometer or jam boiling thermometer).
B. Passion Fruit Jam
- Sugar 49%
- Fruit juice 20%
- Skin pulp 20%
- Water 11%
- Sodium bicarbonate 0.02%
- Passion fruit juice has a pH 2.6-3.0 and a high starch content. The bigger fruits (more than 30g) are more suitable for food processing as they have more juice and less rind. The fruits are most suitable for processing when all greenness has disappeared and the outer skin has a smooth or slightly crinkled surface.
- The fresh whole fruit can only be stored for a few days at ambient temperature before it deteriorates. At 6.5°C they can be stored for 3-4 weeks. The pulp can be stored for long periods in bulk with 1000-1500ppm sulphur dioxide or benzoic acid or a mixture of both, but there is a reduction in the quality of the flavor. During heat preservation the main problem to overcome is the loss of the extremely heat sensitive flavor, which is susceptible to quick oxidation.
- Sodium bicarbonate is added to adjust the pH of the juice. The optimum pH to give a good gel is pH 3.0.
- Wash whole fruits in clean water and discard any bad fruits.
- Cut fruits in half with a stainless steel knife and scoop out the pulp with a stainless steel spoon.
- Extract the juice from the pulp by liquidizing it at a very low speed (this stops the chipping of the seeds, which gives black specks in the jam that are very hard to remove and look like dirt) for about one minute. Tip the contents into a muslin cloth and squeeze out the juice leaving the seeds behind. This method will give a yield of raw juice from whole fruit of between 30-35%.
- To make skin pulp take the same quantity of skins, as skin pulp required. Boil the skins for about 30 minutes, until the flesh of the skin is soft and translucent. Remove the skins from the water and scoop out the flesh from the outer cuticle. Liquidize this softened flesh with water, (2 parts softened flesh, to 1 part water -use the water in which the skins were boiled as this contains pectin washed out during the boiling) to a smooth cream. Squeeze the mixture through a muslin cloth to remove hard pieces of pith. Skin pulp is added to the jam as it contains natural pectin and saves adding artificial pectin which is expensive.
- Mix the juice with sodium bicarbonate before boiling. If the bicarbonate is added during boiling the jam will bubble up over the top of the pan.
- Boil all the ingredients in a stainless steel pan until it reaches the ‘end-point’. Jam should not be boiled for more than 12-15 minutes as it can develop a caramelized taste, become too sweet or discolored. By reducing the amount of water that is added, the boiling time can be reduced.
- The end point is reached when the total soluble solids content is 70%. This is measured using a refractometer. Jam with over 70% sugar may crystallize during storage.
- The end point is usually reached when the temperature is 106-108 deg C. When the jam is nearly at this temperature, a small amount is removed and tested with a refractometer. The sample must be cooled before it is measured. It is important that the utensils used are dry to get an accurate reading.
- It is important to stir the jam at all times during heating to prevent burning at the bottom of the pan.
- When the endpoint has been reached, the jam is filled into clean, sterile glass jars. The jars should be sterilized with boiling water or steam and should be hot when they are filled to prevent them from cracking.
- The jars should be filled as quickly as possible so that the jam does not continue cooking for longer than needed. The tops of the jars should be wiped clean with a clean cloth and the lids placed on.