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1. Fruit and vegetable products


Nutritional significance
Processing
Jams, jellies, marmalades and fruit cheeses
Chutney, pickles, and sauces
Dried fruit and vegetables
Processing notes
Packaging
Suitability for small-scale production

Many organizations, from both the government and non-government sectors, are actively promoting the processing of fruit and vegetables. The reasons for this include:

· Attempts to preserve seasonal gluts which often lie rotting on the roadside.
· Difficulties in storing large quantities of fresh produce without incurring heavy losses.
· Small local markets for the large quantities of fresh produce in season.
· Ineffective distribution and transportation to meet demand in other, often urban, areas.

Due to the above constraints, rural producers are often forced to give produce away or let it rot. To prevent this loss, many may be tempted to convert such gluts into value-added products to be sold in the urban areas. However, before production begins, it is advisable that the market is assessed, and that demand for the processed product is determined. A surplus of fresh food is not sufficient reason for starting production.

Pineapples left to rot in time of glut

Many indigenous fruit and vegetable products such as fruit leathers, fruit pastes/jams, pickles, and dried chips are made in the home. These preserved products are usually stored for future use and are often not intended for sale.

In some countries, the advance of tourism and the growth of an urban middle class has produced a developing market for a wide range of western-style products including jams, jellies, and crystallized fruit sweets. Existing products are often made on an industrial scale, have sophisticated packaging, and are promoted by extensive marketing campaigns. Therefore, if a small-scale producer is aiming to compete effectively, the maintenance of high quality, in terms of both product and packaging, and keeping costs low is essential.

Nutritional significance

Fruits and vegetables provide an abundant and cheap source of vitamins, minerals, and fibre. Their importance in the diet is largely determined by culture, for example, a religion such as Hinduism demands that its followers are vegetarian and their diet therefore contains a high proportion of fruit and vegetables. Other communities, however, only serve vegetables as accompaniments to main meals, and fruits as appetizers and desserts.

It is preferable to consume fruit and vegetables when fresh, as the nutritional content is then usually at its highest. Some techniques, such as blanching, leach out many water-soluble vitamins into the surrounding liquid and if this liquid is not consumed, many nutrients are lost. Other methods such as sterilization expose the food to high temperatures which destroy some of the B vitamins. The table below illustrates the stability of nutrients, when exposed to certain processing or storage conditions.

Stability of vitamins under different conditions

Nutrient

Air

Light

Heat

Maximum cooking losses (per cent)

Vitamin A

U

U

S

40

Vitamin C

U

U

U

100

Biotin

S

S

U

60

Vitamin D

U

U

S

40

Vitamin K

S

U

S

5

Pyridoxine (Vitamin B6)

S

U

U

40

Riboflavin (Vitamin B2)

S

U

U

75

Thiamine (Vitamin B1)

U

U

U

55

S = stable (no important destruction)
U = unstable (significant destruction)

The importance of these losses depend on the actual nutritional status of an individual consumer (for example, the nutrients they are lacking, and the amount needing to be consumed).

Processing

Although there are many similarities between the processing of fruit and vegetables, it is important to realize the following differences.

Fruits are nearly all acidic and are commonly called 'high acid' foods. This acidity naturally controls the type of micro-organisms that are able to grow in fruit products. The spoilage microorganisms that are likely to be found in such products are moulds and yeasts, which if consumed, rarely cause illness. Processing may be achieved by using preservatives such as sugar, salt and vinegar, and by drying, concentration or fermentation.

Vegetables are less acidic than fruits and for that reason are classified as 'low acid' products. A wide range of micro-organisms are able to grow in moist low-acid products, which may lead to spoilage and the possibility of food poisoning. To prevent this, vegetables can be processed by heating to destroy bacteria, or by pickling, salting, or drying to inhibit bacterial growth. Care is needed when processing low acid products, such as vegetables, to minimize the risk of transmitting food poisoning bacteria to consumers.

Jams, jellies, marmalades and fruit cheeses

Collectively known as preserves, these products are finding an increased importance in many countries, particularly in the more affluent urban areas. Fruit is most commonly used as the raw material, but some vegetables such as pumpkin can be used.

The principles of preservation involve heating to destroy enzymes and micro-organisms, combined with a high acidity and sugar content to prevent re-contamination. The mix of ingredients is quite complex, but basically involves the correct combination of acid, sugar, and the gelling compound 'pectin' (pectin is present naturally in plants, but may also be added in a commercially-produced form), to achieve the desired gel structure. The ingredients are then boiled together to evaporate water and achieve the correct sugar content.

Jams

This is a solid gel made from fruit pulp or juice, sugar, and pectin. It can be made from a single fruit or from a combination, but in either ease the fruit content should be at least 40 per cent. In mixed-fruit jams, the first-named fruit should be at least 50 per cent of the total fruit added (based on European legislation). The total sugar content of jam should not be less than 68 per cent to prevent mould growth after opening the jar.

Jellies

These are crystal-clear jams, produced using filtered juice instead of fruit pulp.

Marmalades

These are produced mainly from clear citrus juices and have fine shreds of peel suspended in the gel. Commonly-used fruits include limes, grapefruits, lemons and oranges. Ginger may be used alone or in combination with the citrus fruit. The fruit content should not be less than 20 per cent citrus fruit, and the sugar content is similar to jam.

Fruit cheeses

These are highly boiled jam-like mixtures that have a final sugar level of 75-85 per cent and thus set in a solid block. They can be cut into bars or cubes, or further processed as ingredients in confectionery or baked goods.

The table below outlines the stages needed for the production of some fruit and vegetable products:

Production stages for some preserves

Process/product

Prepare raw material

Pulp/extract

Sieve

Strain

Add other ingredients

Boil

Fill

Pack

Jam (whole-fruit)

*




*

*

*

*

Jam

*

*

*


*

*

*

*

Jelly

*

*


*

*

*

*

*

Marmalade

*

*


*

*

*

*

*

Fruit cheese

*

*

*



*

*

*

Equipment required

Processing stage

Equipment

Section reference

Prepare raw material



Fruit and vegetable cleaners

14.1

Peeling machinery

51.0

De-stoners

21.0

Fruit and vegetable choppers

12.1

Cutting, slicing and dicing equipment

17.0

Pulp/extract


Fruit presses

53.1

Pulpers/juicers

55.0

Juice centrifuges

07.3

Sieve/strain

Sieves

29.3

Strainers

29.4

Add other ingredients

Weighing and measuring equipment

64.1 and 64.2

pH meters

52.0

Refractometer

56.0

Boil

Boiling pans or Steam jacketed pans

48.0

Thermometer

63.0

Heat source

36.0

Fill

Solid filling machine

28.2

Pack/seal

Sealing machine

47.1

Capping machine

47.2

Cutting pineapple

Preparation of the raw material

The process begins with washing the incoming raw materials, and it is vital that the water used is potable. In some regions it may be difficult to obtain a supply of clean water and it may be necessary to purify it. This can be carried out by boiling the water and allowing it to settle, but this is a slow process and is costly in terms of fuelwood. It is possible to purchase water-filters or make your own. In all cases it is advisable that local expert advice is sought on the suitability of the water in any location before processing takes place.

Pulping/juice extraction

Juice can be extracted in a number of ways:

· by steaming the fruit
· by reaming the fruit (for citrus fruit)
· by pressing
· by pulping, using purpose-made pulpers, blenders, or a pestle and mortar.

Straining

The starting material for the production of jellies is a clear juice. To achieve this, the extracted juice must be strained using a muslin cloth bag. Additionally, sugar syrups should be strained in order to remove any unwanted material.

Addition of ingredients and process control

As in all processing, it is necessary to ensure that the correct amounts of ingredients are added, and that temperatures and other process conditions are standardized. This will ensure that the product has constant quality time after time. To standardize recipes successfully it is useful to have the following:

· a pH meter or pH papers for checking the acidity level (the optimum range is 3.0-3.3)
· a thermometer for temperature measurement
· accurate scales for the measurement of small amounts of ingredients such as preservatives
· a refractometer for accurately assessing sugar content.

(Note: the boiling temperature can also be used as a less accurate measure of sugar content. The advantage is that a thermometer is cheaper than a refractometer.)

Boiling

Boiling can be carried out in a stainless steel or enamelled metal pot. If pans made from other materials are used there is the possibility that the fruit acids will react with the pan and cause 'off' flavours. For larger production it is best to use a steam jacketed pan.

There are two heating stages in the manufacture of jam. Initially, it is necessary to heat the fruit slowly in order to soften the flesh and extract the pectin. Once this is completed, it is vital to boil the mixture rapidly. This change in heat output is difficult to achieve without an easily-controllable heat source and the choice of heat source should be an important consideration before embarking on production.

Filtering sugar syrup

Filling jam into bottles

During boiling care must be taken to avoid localized overheating which is likely to lead to burning and colour change. Boiling is carried out until the desired sugar content is reached. There are various ways to test for this. It can be conveniently measured using a hand-held refractometer, or a sugar thermometer. These may be out of financial reach for a small producer, but if a product of consistent quality is to be produced, batch after batch, their use is highly recommended. Alternative checks, including placing a drop of the product in cold water to see if it sets, are less accurate, and require experience and skill to work effectively.

Filling and packaging

A good product packed in a dirty container will soon deteriorate, therefore it is essential that the containers used are thoroughly washed and sterilized. (For details refer to the Packaging chapter.)

The preserve should be hot-filled into suitable containers which are then sealed with a lid. The temperature of filling is important too hot, and the steam will condense on the inside of the lid and drop down onto the surface of the preserve. This will dilute the sugar on the surface and allow mould growth. If the temperature is too low, the preserve will thicken and be difficult to pour and a partial vacuum will not form in the jar. Ideally the temperature should be 82-85°C.

Filling can be achieved using jugs and simple funnels. For higher production rates small hand-operated or semiautomatic piston-fillers are available. In all cases, the jars should be filled to the correct level, approximately 9/10ths full, to assist the formation of a vacuum as the product cools.

Finally, the jars are held upright while the gel is formed during cooling. This can be done by standing the jars on shelves, or, more quickly, using a low-cost water-cooler (see Packaging chapter for more details). A partial vacuum should form between the surface of the jam and the lid when the product cools. This can be seen by a slight depression in the lid. If a vacuum does not form, it means that the jar is leaking or the filling temperature was too low.

The packaging is likely to be one of the main costs involved in production. Ideally, glass jars should be used, with new metal lids. It is possible to use paper, polythene, or cloth tied with an elastic band or cotton, to cover the jars. The appearance of the product is, however, less professional, and there is a risk of contamination by insects. This is not recommended unless metal lids are impossible to obtain.

Increasingly, products are being packaged in pots with aluminium foil lids by large manufacturers. These packs are becoming popular with urban consumers as they are cheaper and more convenient than glass. However, they are difficult to obtain in many countries and are often expensive. Alternatives include plastic pouches/sachets. Technical advice should be sought if these packs are being considered.

Chutney, pickles, and sauces

These products are popular in some regions where they are used as accompaniments to meals. There are hundreds of varieties in existence and they can be made from a wide range of fruits and vegetables.

The basic principle of preservation for all of these products is the use of acetic acid (vinegar). Acetic acid preserves the product by making the environment acidic, and by so doing it inhibits the growth of spoilage and food-poisoning micro-organisms. Other ingredients such as salt and sugar add to the preservative effect.

Chutney

These are jam-like mixtures which have added vinegar and spices. The high sugar content exerts a preservative effect, and a high level of vinegar addition is not always needed. These products are hot-filled.

Pickles

Pickles can be either fermented or unfermented, sweet or sour, and can be made from either whole or chopped fruit.

Sauces

These are thick liquids made from pulped fruit and/or vegetables, with the addition of salt, sugar, and vinegar. They require pasteurization and are filled while hot.

The table (right) outlines typical processing stages for a representative range of products.

Product

Sweet pickle fermented

Sour pickle fermented

Unfermented pickle

Sauce

Select fruit/ vegetable

*

*

*

*

Prepare fruit/ vegetable

*

*

*

*

Add to brine solution and mix

* 5% brine + 1-2% sugar; leave for 1-2 weeks

* 5% brine; leave for 1-2 weeks



Add salt



*

*

Mix with vinegar




*

Boil




*

Prepare vinegar mixture and boil

* 3% salt 5% vinegar and sugar

* 3% salt + 5% vinegar

* 3% + 6% vinegar and sugar


Pour hot vinegar mixture over the vegetables/fruit

*

*

*


Pack (seal and label)

*

*

*

*

Pasteurize




*

Equipment required

Processing stage

Equipment

Section reference

Prepare raw material



Fruit and vegetable cleaners

14.1

Peeling machinery

51.0

De-stoners

21.0

Fruit and vegetable choppers

12.1

Cutting, slicing, and dicing equipment

17.0

Blanch

Steam blancher

01.0

or boiling pan

48.0

Heat source

36.0

Mix sugar and other ingredients

Weighing and measuring equipment

64.1 and 64.2

Brine meter

64.6

Boil

Boiling pan

48.1

Heat source

36.0

Thermometer

63.0

Fill

Liquid filling machine

28.1

Solid filling machine

28.2

Pack

Capping machine

47.2

Sealing machine

47.1

Pasteurize

Water bath and large boiling pan

48.0

Pasteurizer

50.0

Peeling apples

Preparation of the materials

Equipment needed for de-stoning and cutting are as indicated in the section for jams.

Addition of ingredients

To ensure that the product has a long shelf-life, it is necessary to balance the sugar concentration and acidity. To do this it is likely that the following pieces of equipment will be necessary:

· pH meter
· Brine meter
· Refractometer.

It is possible to calculate a value known as the 'preservation index'. This is used to assess whether the product is safe from food spoilage and poisoning micro-organisms. The value can be calculated as follows:

If you do not have access to basic laboratory equipment or are not sure how to carry out the calculation, it is best to take the sample to a food-testing laboratory and they will be able to tell you whether you need to adjust the recipe.

Pasteurization

Pickles, which have an adequate preservation index, do not need to be pasteurized. However, as an additional safety measure, it is common to boil the vinegar mixture, add it to the vegetables, and fill the product into the jars while it is still hot. In this way the hot mixture will form a partial vacuum in the jar and prevent recontamination.

Sauces can be pasteurized before filling using a stainless steel pan or a steam jacketed pan, depending on the rate of production. Alternatively, pasteurization can take place after filling by placing the filled containers with the lids loosely on in a pan of boiling water and the water level around the shoulder of the jar. The time required for pasteurization will depend on the product, but most sauces are heated to between 80-95°C for five to ten minutes.

Filling and packaging

The same considerations for sterilizing and filling bottles apply as for jams. Glass jars are the most commonly-used packaging material. Pickles may also be packed in small quantities in polythene pouches. These simple pouches are sealed with a powered bar-sealer. To avoid seepage, it is suggested that a double pouch be used (i.e. an inner pouch made from food-grade polythene placed in an outer pouch made from cheaper polythene, and a label between the two).

Dried fruit and vegetables

Drying produce in the sun is simple and has the advantage of being a traditionally-understood technology with little or no fuel and equipment costs.

Drying removes water from the surface of the food by the combined effects of air flow, air temperature, and air humidity. The relationship between the three is important if drying is to be successful. When the moisture content is lowered below a certain level, micro-organisms cannot grow, and the produce is preserved.

In humid climates, dried products must be packaged well in order to prevent moisture uptake and protect against spoilage.

Air-dried products

These are the most common type of dried fruit and vegetables. Some products may be blanched or sulphured/sulphited to protect the natural colour and aid preservation. Dried fruit pulp is often named 'fruit leather'.

Dried and fried products

These are products which are partly dried, and then deep-fried, to produce a snack food. Examples include banana chips and bombay mix.

Osmotically dried fruits

These are fruits which are soaked in hot concentrated sugar syrups to extract some of the water prior to drying.

Production stages for dried fruits and vegetables

Process/product

Air-dried fruit

Air-dried vegetables

Fried/dried product

Osmotically dried fruits

Prepare raw materials

*

*

*

*

Blanch


*



Sulphuring/sulphiting

*Some

*Some



Prepare sugar syrup




*

Soak in syrup




*

Pulp

*Some (e.g. fruit leathers)




Strain/filter

*Some (e.g. fruit leathers)




Boil

*Some (e.g. fruit leathers)


*


Pour into thin sheets

*Some (e.g. fruit leathers)




Dry

*

*

*

*

Deep-fry



*


Pack

*

*

*

*

Equipment required

Processing stage

Equipment

Section reference

Prepare raw material

Fruit and vegetable cleaners

14.1

De-stoners

21.0

Peeling machinery

51.0

Fruit and vegetable choppers

12.1

Cutting, slicing and dicing machinery

17.0

Blanch

Steam blancher 01.0 or boiling pan

48.0

Sulphur/sulphite

Weighing and measuring equipment

64.1 and 64.2

Sulphur cabinet


Prepare sugar and syrup

Weighing and measuring equipment

64.1 and 64.2

Boiling pan

48.0

Heat source

36.0

Soak in syrup

Boiling pan

48.0

Food grade tank

03.1

Pulp

Pulper/juicer

55.0

Strain/filter

Muslin cloth


Stainless steel strainer/filter

29.0

Dry

Solar dryer

23.1

Fuel-fired dryer

23.2

Electric dryer

23.3

Deep-fry

Fryers

33.0

Pack

Sealing machinery

47.1

Processing notes

During drying, many fruits and vegetables experience some changes in colour. These can be lessened by carrying out some simple processing stages prior to drying (for example, blanching, sulphuring, and sulphiting).

Blanching is a short heating treatment in water or steam, and is often a necessary processing stage. It has many functions, but essentially it destroys enzymes which are responsible for causing browning, and reduces the total number of micro-organisms in the food.

For production on a small scale, the produce can either be wrapped inside a muslin cloth or in a wire basket, and immersed into boiling water. As the food is in direct contact with the water there is some loss of water-soluble vitamins. Steam blanching can be carried out by placing the produce in a strainer, which is then fitted over a pot of boiling water and covered with a lid to prevent the steam escaping. Steaming takes a few minutes longer than the water method but it has the advantage of losing fewer nutrients, as vitamins are not leached into the water. For larger production, a tray blancher can be purchased.

Sulphuring/sulphiting

With some dried products, the use of chemical preservatives will improve the colour and increase the shelf-life. The most commonly used preservative is sulphur dioxide. There are two methods: sulphuring and sulphiting. Sulphuring is more commonly used for fruits, and sulphiting for vegetables.

Sulphiting involves the use of sulphite salts, such as sodium sulphite or sodium metabisulphite. They may be either added to the blanching water or more commonly used by soaking the food in a solution of the salts.

The strength of a sodium metabisulphite solution is expressed in 'parts per million' (ppm) and the strength used will depend both on the final product required and the legal standards set in any particular country.

Sulphuring is achieved by burning sulphur in a sulphur cabinet. This can be made from locally available materials. The amount of sulphur used and the time of exposure depend on the commodity, its moisture content, and the levels permitted in the final product. The food is placed inside the cabinet and sufficient sulphur is placed in a container near the trays. For most vegetables 10-12 g of sulphur (22½ level teaspoons) per kg of food is adequate. The sulphur is ignited and allowed to burn in the enclosed cabinet for 1-3 hours.

Drying techniques

The simplest method of drying is to lay the foods in the open air, either on mats, or on raised platforms. Although this is effective, there is limited control over the drying process which results in a variable product quality and a greater risk of contamination. To give more control over these aspects, solar dryers have been designed which protect the product from dirt and insects and increase the rate of drying.

Solar dryers fall into two categories - direct or indirect. In a direct dryer, the product is exposed to the sun's rays. This exposure results in vitamins being lost and a darkening in the colour of some foods. This colour change is desirable for products such as dates, but for lighter fruits, such as papaya and apricots, it is a problem.

Indirect dryers shelter the product from the sun. The heat from the sun is collected in a separate connected chamber and the heated air is passed over the food in an enclosed dryer.

Designs are also available for combined dryers. These are fitted with both a heater unit and a solar collecting chamber. When there is plenty of sunshine, the solar collector can be used, but the heater can also be used in poor weather conditions and at night.

There have been numerous designs for solar dryers, but most have met with a very poor response from rural producers. Most rural consumers are not willing to pay more for a slightly improved product quality and the investment in a dryer may not prove to be economically advantageous. In addition the relatively poor control over drying conditions compared to that for fuel-fired or electric dryers, means that they are largely unsuitable for high-value products such as spices, where an improvement in quality does generate higher income.

There are also a large number of designs of fuel-fired dryers. These have better control over drying conditions and therefore produce a higher quality product. They are able to operate at all times of the day and year, and in most cases produce a higher rate of drying. However, these benefits must be evaluated against higher capital and operating costs.

Sulphur cabinet

Packaging

Traditional packaging materials such as baskets, jute sacks, and wooden boxes have long been established for packaging dried foods such as fish and vegetables. They are for commodities which are transported in large quantities to a central marketing place and then sold loose. These packages can be used several times and are usually cheap.

Traditional packaging is only suitable provided the climate does not cause an increase in the moisture content of the food which will result in mould growth. If the climate is not suitable, dried foods should not be transported in this way. Boxes are used to prevent crushing of dried foods, and in humid climates, moisture-proof flexible films can be used (see Packaging chapter).

Some semi-moist foods such as osmotically dried fruits have special needs to prevent the reabsorption of water. Since dried fruit is a valuable product, it may be worth spending more on the package, such as a moisture-proof sealed bag. A wide range of flexible packaging materials is also available, but the use of many of these is limited due to high costs. Low-density polyethylene is a moderately good moisture barrier and cheaper than other films. It can be easily sealed using a powered bar-sealer.

Flexible materials may be used as the sole component of a package, but for most foods, a sturdy outer container is also needed to prevent crushing or to exclude light.

Suitability for small-scale production

It is technically feasible to make most fruit and vegetable products on a small scale using simple machinery, but it is likely that a group starting up in business will require substantial advice.

A common problem for small producer groups is the lack of market research. Such enterprises are often production-led, and products may be manufactured in order to use up a glut before a definite need or market for the product has been identified. Therefore, marketing will require special emphasis as this is often the most serious problem facing a new business. Rural production of value-added fruit products for urban or middle class markets has the added complication that the markets may be a long way from the producer group which may cause difficulties in negotiations and language problems, packaging supplies, and high distribution costs.

It is a common mistake to assume that poor-quality fruits and vegetables can be used to make high-quality goods. It is only possible to use rejected produce if it has been rejected for cosmetic reasons (e.g. the wrong size or slight blemishes).

For year-round production, it may be necessary to part-process raw materials into a form that can be stored in readiness for future production. Alternatively, a sequence of fruits or vegetables can be processed throughout the year in some regions. Both methods can help overcome the highly seasonal nature of fruit and vegetable crops. Despite this, in many cases processors will need a high working capital to buy the majority of raw materials in mid-season when prices are at their lowest.

A constraint in the production of preserves is that they require a large quantity of sugar. In many cases, refined white sugar has to be brought from urban centres, and may be expensive.

These points are not meant to discourage anyone from starting such a venture, but the problems should not be under-estimated, and it is best to seek advice first from a qualified technical source.


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