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Technical Briefs and Manuals: English
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As the name suggests, lime marmalade is a preserve made from limes and sugar. Marmalades can also be made from other citrus fruits - notably oranges, lemons, grapefruit or a mixture of any of these. This recipe is based on practical experiences of making lime marmalade in the West Indies. When using other citrus fruits or limes that are grown in a different region, it is likely that minor modifications to the formulation will be needed to account for the different levels of acidity.
The production of traditional lime marmalade by the small-scale processor is perfectly feasible provided the equipment is available and the general principles for jam making are understood and followed.
Lime marmalade is made according to the basic principles of jam and marmalade production. However, there are two potential problem areas which the processor should be aware of:
1. Lime is unusual in that it has a very high acidity (and low pH). Jams and jellies need to have a pH between 3.0 and 3.3 to enable the pectin to set the gel. Most fruits lie in this pH range but if they have a pH higher than 3.3, citric acid can be added to the fruit to bring the pH down to the required range. Lime juice however has a pH of 2.7 to 2.9 and therefore the pH has to be increased. It is possible to do this quite easily by adding sodium bicarbonate (baking powder) to the fruit pulp.
In the experience in the West Indies, it was found that the addition of 20g of sodium bicarbonate per litre of lime juice was sufficient to give the required pH adjustment. In each situation, it is important to get the correct pH, which should be done by adding sodium bicarbonate to the lime juice and measuring the acidity with a pH meter.
If a pH meter is not available, it may be necessary to seek outside advice. Alternatively, the amount to add can be determined by trial and error. Carry out a series of small trial batches using different levels of bicarbonate and find out the best level by checking the set of the marmalade.
2. The second problem in marmalade production is getting an even distribution of shredded peel throughout the product. If the correct technique is not used the peel tends to float to the surface of the jar during setting. It is important to soak the peel slices in a sugar solution before they are added to the marmalade to increase their density. This means that the marmalade making process is somewhat longer than for jam making and planning for production should take this into account.
At first glance the production of jams and marmalade may seem like the best option for utilising a glut of fruit. In fact, this is not the case. To make a consistently good quality product requires a certain level of skill and technical input and some specialist equipment – stainless steel boiling pans, refractometer, glass jars and lids for packaging. Preserve making also requires large quantities of sugar and in some cases the addition of pectin, both of which can be expensive ingredients. Therefore, as with all food products, it is essential that the processor carries out a full technical, economic and marketing feasibility study prior to starting the enterprise. Not only will this exercise determine the potential market for the products, it will be a useful tool for planning production and day-to-day running of the business and can be used to approach a bank for a loan if one is required. See the Practical action technical brief on how to carry out a market and technical feasibility study for further information.
1 litre lime juice 20g sodium bicarbonate 3kg sugar 1200g 5 SAG pectin (made up from 40g pectin, 200g sugar, 960ml water) Few drops of green food colour (optional) 200g prepared sugared lime peel
The extraction of lime juice is the most time consuming step for the small-scale manufacturer. It is strongly recommended that if a local commercial lime processor exists, racked juice should be purchased in bulk.
If no such supplier exists then there is no alternative but to extract the juice oneself using small manual or electric squeezers (see Figure 1). It must be remembered at all times that lime juice is very acidic and therefore attacks metals. It is essential to use only good quality food-grade plastic, stainless steel and wooden utensils to collect the juice. The extracted juice must be strained to remove pulp prior to use. If required, lime juice can be extracted and stored in bulk preserved with 1000ppm sulphur dioxide (using 3g of sodium metabisulphite per litre of juice).
The lime peel needs to be cut into very thin strips about 12 to 25mm long and as thin as possible. This is another slow and tedious job which can also be a potential hazard point for contamination by flies and other insects. The cut slices should be kept covered until they are used. A very sharp stainless steel knife should be used to cut the peel into slices. The process can be speeded up by using a small peeler to remove the peel from the limes (see Figure 2) before they are squeezed.
If fresh peel is incorporated directly into the marmalade it will float to the surface during setting and produce a very unsatisfactory product. The shredded peel needs to be saturated with sugar before use so that it has the same density as the marmalade and stayssuspended in the gel andevenly distributed through the jar.
The shredded peel should be well mixed with dry sugar (1kg peel + 1kg sugar) and left in a sealed container for at least a week, mixing occasionally. During this time a sugar solution will form as the moisture from the peel mixes with the dry sugar. The pieces of peel will float in the heavy sugar syrup. Sodium metabisulphate can be added to the sugar (1g per 1kg of peel) to prevent the growth of moulds and yeasts.
This sweet mixture of peel and sugar will be highly attractive to ants and insects. Make sure that the container is covered with a lid or netting and stand it in a trough of water to prevent ants.
The ideal situation is to use commercially available pectin as it has a standard setting power and produces the same product time after time. If it is impossible (or too costly) to buy pectin, it can be extracted from citrus peels or passion fruit rinds, but you will have to experiment on how much to add to the juice to get a good set (see the technical brief on fruit waste utilisation for more information on pectin production).
The best pectin for marmalade is a fast-set pectin. Fast set pectin is preferable because it forms a gel quickly and so holds the pieces of peel in place throughout the marmalade. The usual strength of commercial pectin is 150 SAG. To make a marmalade you need a pectin with a setting power of about 5SAG. Therefore the commercial pectin needs to be diluted (30 times in this case) prior to use.
• Dry mix the pectin and sugar thoroughly. • Heat the water to 70‑75°C and slowly add the sugar/pectin, mix with constant stirring. If a small electric stirrer is available there will be less chance of lumps forming. • Heat to boiling and boil for 1 minute, again with constant stirring. • Hold at 50‑60°C (a double saucepan is useful here).
The technical brief on jams and marmalade production outlines the principles of jam boiling. Ideally a heavy based stainless steel pan or double bottomed jam pan will be available for boiling the mixture. The other desirable pieces of equipment are a wooden stirrer, jam thermometer and possibly a refractometer (figure 3) for testing the total soluble solids and determining the end point of the boiling process.
1. Place the lime juice, bicarbonate and half the sugar in the pan, heat slowly to dissolve the sugar and then bring to the boil. Boil for 3 - 5 minutes with steady stirring (it is impossible to state boiling times exactly, as this depends on the heat source etc).
2. Add the remaining half of the sugar, peel, pectin and green colour and continue boiling until the required sugar level (68%) is reached (as measured either by refractometer, jam boiling thermometer or skill of the producer).
3. Filling and capping Hot fill the finished preserve into clean, dry jars and cap immediately. Care is needed not to fill too hot or too cold, the ideal range being 82‑85°C. Filling whilst too hot can result in drops of steam condensing on the inside of the lid, falling back onto the surface of the product and diluting it to below 68% sugar solids (so that moulds and yeasts can grow). Too cold filling carries the danger of microbiological contamination from the jar etc.
Cap the jars quickly using either screw type or 'Omnia' type push-on lids. When the jars have cooled and a vacuum has formed (about 50°C) rinse them in a bath of clean chlorinated water - one tablespoon of bleach per 4.5 lires of water. Dry the jars and label (see the technical brief on labelling for more details of the legal requirements for food labels).
4. Storage If properly preserved and packaged in glass, marmalade can be stored for up to one year away from direct sunlight. If it is packaged in plastic bottles, it can only be stored for about 4-6 months.
Practical Action Technical Briefs Fruit waste utilisation Jams, jellies and marmalades Food labelling How to carry out a feasibility study
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://www.practicalaction.org/
This technical brief was updated by S. Azam Ali in March 2009. Dr. S Azam-Ali is a consultant in food processing and nutrition with over 15 years experience of working with small-scale processors in developing countries.
This article was added to our catalogue on Monday 25 September, 2006.
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