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Agrodok 3Preservation of fruit andvegetablesIfe Fitz JamesBas Kuipers

This publication is sponsored by: KERKINACTIE.KERKINACTIE attaches high priority to rural development in its work, and supportsorganisations active in this field. Agriculture and food production are activities of vitalimportance in rural areas. Kerkinactie supports this kind of work directly and also indirectlyproviding support for the collection, compilation and spread of information and knowledge. Agromisa Foundation, Wageningen, 2003.All rights reserved. No part of this book may be reproduced in any form, by print, photocopy,microfilm or any other means, without written permission from the publisher.First edition: 1984Second revised edition: 1990Third revised edition: 1997Fourth, completely revised edition: 2003Authors: Ife Fitz James, Bas KuipersEditor: Bas KuipersIllustrator: Mamadi JabbiTranslation: Catharina de Kat-ReynenISBN: 90 77073 302NUGI: 835

ForewordThis Agrodok is meant to be a practical manual giving a review of thesimple techniques used to preserve fruits and vegetables.In addition to information provided in the previous edition of thisAgrodok, this fourth edition covers more theoretical information onfood decay in general, its causes and dangerous effects, as well aspreventive measures that can be taken. In our opinion this knowledgeis necessary if you want to start a small-scale preserving business, towhich a whole chapter is devoted in this edition.The general introduction deals with the principles of spoilage prevention. The various methods of preserving are then explained, and themain points of spoilage specific to the method are covered. The nextchapters deal with jam and juice making and attention is paid to drying vegetables and fruit, as well as salting of vegetables. Freezing isnot discussed, since this technique needs facilities usually not available in many developing countries. We have tried to describe everymethod as practically as possible, including descriptions of the required materials and techniques.Finally we would like to thank some people for their contributions tothe realization of this Agrodok: Domien Bruinsma for writing chapter8 and critically reading the different concepts, Jan Schreurs for textediting, Mamadi Jabbi for making some new illustrations and WillemWürdemann for critically reading the content of this Agrodok.Ife Fitz JamesBas KuipersForeword3

Contents1Introduction22.12.22.3Food spoilage: causes, effects and prevention8What is food spoilage?8What are micro-organisms, and what factors affect theirgrowth?10What do micro-organisms do to fruits and vegetables? 1233.13.23.33.43.53.6PreparationCleaning and washingLye 14.24.34.44.5Preserving by heatingIntroductionPackingPreparationThree types of heatingStorage and gQuality of the fresh productPreparationDrying methodsWhen is the drying process finished?Packing and storageConsuming dried productsThree examples31323234404041426Preserving vegetables with salt and/or vinegar444Preservation of fruit and vegetables6

6.16.26.3Preserving with saltRequirements for saltingPreserving in vinegar7Jam and juice making, syrups, jellies and candied fruit51Making fruit juices52Preparation of other fruit products587.17.288.18.2444849Developing a small-scale food processing enterprise61Marketing a fresh or processed product62Organizing a processing enterprise64Further reading68Useful addresses70Appendix 1: Pasteurization of fruits and vegetables72Appendix 2: Sterilization in a boiling water bath74Appendix 3: Sterilization in a pressure cooker or autoclave76Appendix 4: Preparation and drying conditions79Appendix 5: Preparation of vegetables for salting83Appendix 6: Juice extraction methods84Glossary86Contents5

1IntroductionAll living creatures, including humans, depend on nature for theirfood. Humans are not only hunters and gatherers, but also farmers. Welive from hunting and fishing, agriculture and animal husbandry. Mostof our food consists of agricultural products, which are usually seasonal and spoil quickly. To make food available throughout the year,humans have developed methods to prolong the storage life of products: to preserve them. The rotting process can be postponed by adding preservatives, optimizing storage conditions, or applying moderntechniques. The last option will not be discussed in this Agrodok. Thisbooklet focuses on the traditional preservation methods still commonly used in developing countries for fruits and vegetables.Fruits and vegetables provide an abundant and inexpensive source ofenergy, body-building nutrients, vitamins and minerals. Their nutritional value is highest when they are fresh, but it is not always possible to consume them immediately. During the harvest season, freshproduce is available in abundance, but at other times it is scarce.Moreover, most fruits and vegetables are only edible for a very shorttime, unless they are promptly and properly preserved.This Agrodok will focus on a few simple and relatively inexpensivepreservation techniques that can be applied on a small scale by anindividual or a small group (of families for example). Chapter 2 provides information on food spoilage in general, its causes and dangerous effects, as well as measures that can be taken to prevent it. Specific knowledge is needed to apply the right preservation methods.Fruits and vegetables have to be specially prepared, for example, before they can be preserved. How this is done is explained in Chapter 3.Chapters 4 to 7 describe the various preservation methods: heating,drying, and the use of additives such as salt and sugar. In times ofscarcity, preserved food can be sold for a good price. It can even beworthwhile to start a small preserving business. Chapter 8 explainswhat this would involve. More information can be found through the6Preservation of fruit and vegetables

addresses and literature listed in Chapter 9 and in the appendixes thatfollow, which provide specific information on how to prepare andpreserve the various types of fruits and vegetables. Various terms thatmay be new to readers are defined in the glossary at the end of thebooklet.Agromisa welcomes all readers’ comments that could contribute toimproving the quality of our publications. A survey form is thereforeincluded in the middle of this booklet, which can be completed andreturned to us. Readers seeking more information on food preservationare also encouraged to contact Agromisa’s Question and Answer Service at the address listed in the back of this booklet.Introduction7

2Food spoilage: causes, effectsand prevention2.1What is food spoilage?Every change in food that causes it to lose its desired quality andeventually become inedible is called food spoilage or rotting. As notedearlier, this Agrodok focuses specifically on fruits and vegetables. Aslong as they are not harvested, their quality remains relatively stable –if they are not damaged by disease or eaten by insects or other animals. However, the harvest cannot be postponed indefinitely: whenthe time is right, it is time to act. As soon as the fruits and vegetablesare cut off from their natural nutrient supply, their quality begins todiminish. This is due to a natural process that starts as soon as thebiological cycle is broken by harvesting. Once it is harvested, the agricultural product is edible for only a limited time, which can vary froma few days to weeks. The product then begins to spoil or ‘rot’. Wedistinguish between various types of spoilage:123456physical spoilagephysiological agingspoilage due to insects or rodentsmechanical damagechemical and enzyme spoilagemicrobial spoilagePhysical spoilage is caused for example by dehydration. Physiologicalaging occurs as soon as the biological cycle is broken through harvesting. Neither process can be prevented, but they can be delayed by storing the agricultural products in a dry and draft-free area at as low atemperature as possible.Insects and rodents can cause a lot of damage. Not only by eating theproducts, but also by passing on micro-organisms through their hair8Preservation of fruit and vegetables

and droppings. The affected parts of the plants are then especiallysusceptible to diseases.Chemical and enzyme spoilage occurs especially when vegetables andfruit are damaged by falling or breaking. Such damage can releaseenzymes that trigger chemical reactions. Tomatoes become soft, forexample, and apples and other types of fruit turn brown. The fruit canalso become rancid. The same processes can also be triggered by insects: the fruit becomes damaged, which causes enzymes to be released. Enzymes can be deactivated by heating the fruit or vegetables.The same effect can be achieved by making the fruit or vegetablessour or by drying them, but the enzymes become active again as soonas the acidity is reduced or water is added.The peel of a fruit or vegetable provides natural protection againstmicro-organisms. As soon as this shield is damaged by falling, crushing, cutting, peeling or cooking, the chance of spoilage increases considerably. Crushing occurs most often when fruits or vegetables arepiled up too high.To prevent harvested products from spoiling, they can be preserved:physiological aging and enzyme changes are then stopped and microorganisms are prevented from multiplying on the product. To retainthe desired quality of a product longer than if it were simply storedafter harvesting, it must be preserved. To preserve food it must first betreated, with the goal of stopping physiological aging and enzymechanges and preventing the growth of micro-organisms.Before discussing the specific treatment methods, we will first focuson the subject of micro-organisms. What are micro-organisms? Whyare they dangerous? How can you prevent them from making yousick? The answers to these questions will help you understand thesteps required to safely preserve food.Food spoilage: causes, effects and prevention9

2.2What are micro-organisms, and whatfactors affect their growth?Micro-organisms are very small, one-celled animals. There are threetypes: bacteria, moulds and yeasts. Bacteria and yeasts cannot be seenwith the naked eye, but moulds are often visible because they formvisible thin threads (filaments) or a solid cluster. Just like humans,micro-organisms require certain minimum living conditions. Theycannot survive without:? sufficient water? oxygen? the right degree of acidity? nutrients? the right temperatureWater is necessary for maintaining many physical processes. Wherethere is a shortage or lack of water micro-organisms cannot grow, suchas in dried legumes. Drying is therefore one way to prevent spoilage.Meat and fish do not have to be 100% dry in order to preserve them.By adding salt, the remaining water becomes unsuitable for microorganisms. The same effect can be achieved by adding sugar to fruit.Enzymatic spoilage is also inhibited by drying.Most micro-organisms need oxygen. If there is a shortage of oxygen,it is difficult for bacteria to survive, let alone multiply. But there arealways a few that manage to survive. As soon as the oxygen supply isincreased, these remaining bacteria will again grow and multiply.Some types of micro-organisms even thrive in an oxygen-poor environment.Bacteria grow best in an environment that is not too acidic. Lessacidic products are therefore especially susceptible to bacterial spoilage. Examples of such products are meat, eggs, milk and various typesof vegetables. Beer, yoghurt, wine, vinegar and fruit are less sensitivebecause they are more acidic. Adding acidity to products slows downthe process of microbial spoilage. The degree of acidity is measured asa pH level. A neutral product like milk has a pH of 7; meat has a pH of10Preservation of fruit and vegetables

about 6, carrots have a pH of 5 and oranges about 4. The more acidic aproduct is, the lower the pH value will be.Just like humans, micro-organisms also need nutrients: sugars, proteins, fats, minerals and vitamins. These are rarely in short supply,because they can be found in all food products.To thrive, micro-organisms need a temperature of between 5 and65 C. At temperatures above 65 C it becomes very difficult for themto survive; and they definitely die if boiled, as long as they are boiledfor a certain length of time, such as 10 minutes. When heated, themicro-organisms slowly die off, but not all at the same time. Heatingat temperatures lower than 100 C thus has to be sustained for a longerperiod. The growth of micro-organisms is also slowed down significantly at temperatures between 0 and 5 C (as in a refrigerator), whichmakes it possible to store the food products for a few additional days.At temperatures below 0 C microbial growth is stopped completely,but the micro-organisms themselves remain alive. They will becomeactive again as soon as the temperature rises above 0 C.To preserve food, it is sometimes necessary to make drastic changes tothe micro-organisms’ living conditions. We can remove water (drying), increase the acidity, or first heat the products (to kill the bacteria)and then store them in air-tight containers to prevent oxygen fromentering (preserving/canning). These and other methods will be discussed later in this booklet.Do micro-organisms grow differently on vegetables and fruit?Vegetables and fruit have a lot in common. But there are also important differences, which determine the type of spoilage they are mostsusceptible to. Damaged fruits, which are usually somewhat acidic,are very susceptible to the growth of yeasts and moulds. Vegetablesare generally less acidic, and their spoilage is usually caused by bacteria. Though not visible to the naked eye, bacteria can still be presentin large numbers.Food spoilage: causes, effects and prevention11

What types of micro-organisms grow on what products? Moulds can be found on al