practical application of solar tunnel dryers

8/2/2019 Practical Application of Solar Tunnel Dryers

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Practical Application ofSolar Tunnel Dryers

Klaus Triebe, ELNATAN (Association inc. under section 21)

P.O. Box 161 Calitzdorp 6660 South Africa

[email protected] Tel/Fax++27 44 2133 859

International Solar Food Processing Conference 2009 India, Indore 14 16 January 2009


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Table of contents1. Abstract

2. Introduction

3. Background

4. Project

1. Fruit Leather

1. Preparation of drying moulds.

2. Preparation of fruit

3. Grinding of fruit

4. Mixing of fruit pulp

5. Drying of fruit leather

6. Storage

2. Fruit Juice Concentrates

1. Preparation of Dryer

2. Concentration of juices in the dryer

5. Conclusion

Abstract Solar Tunnel Dryers (STD) are weather protected food dehydration tunnels

that dry food economically and hygienically. STD are used to dry fruits and fruit pulp as well as concentration of fruit

, . Fruit leather is prepared sorted and washed and fruits, which is then

shredded with common Kitchen machines. The fruit pulp is mixed with preservatives and sugar and volumetrically

distributed unto plastic lined mould. After drying the fruit leather is stored ina cool room until finally packed or refined with chocolate.

Fruit juices are concentrated in a STD using similar drying moulds as for thefruit leather. The dryer has to be equipped with an absolute level grid toreceive the moulds.

Sterilised fruit juice is poured into moulds to a depth of 2-3 cm forevaporation. 50% of the water content is evaporated on the first day.Thereafter the evaporation slows down until the final stage of theconcentrate is reached, depending on the requirement of the final product.(E.g. Juice Concentrate, Paste, or Juice Leather)

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Introduction ELNATAN is a non-profitable organisation with a

Christian background. ELNATANs main purpose is tocrea e o s an o ra n a u s n as c s s.has a solar engineering section which has built a 10 m2

Scheffler Reflector, a Solar Tunnel Dryer and massproduces the Lazola box cookers.

ELNATAN has a fruit drying and processing plant wherethe Solar Tunnel dryer is used. Raw materials areprocessed into fruit leathers which are refined withchocolate and o hurt. We also roduce fruit uice

concentrates. All these products are sold to the public inour own shop.

ELNATAN has a further section where standard buildingwork is executed in our district.


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Backgrounda) Our Solar Drying Plant is situated in the south of South Africa in

the Cape Province. We are approx. 100km from the Coast..

c) Our average maximum Summer Temperature is 44 C.d) Average winter minimum Temperature is 2.6 C.e) We have a very dry climate.f) We do have frost in the winter that qualifies to grow fruit from the

prunes family like apricots, peaches, plums and nectarines butalso grapes and quinces as well as citrus fruits. Our fruit has ashort fresh life time and is many times available at low cost,es eciall when the normal market is unable to absorb the excess

fruit at short notice. Weather changes also make necessary toharvest fruit quickly.

g) Some producers are far away from the fresh fruit market and haveno other option than to dry their products.


Background (continue)

h) In our area people have dried fruits for the last 150 years and havealso produced fruit leather. Excessive grape juice was cooked until

substitute.i) Our company is specialised to manufacture fruit leathers and to a

lesser extent grape juice concentrate.

j) Through Heike Hoedt and Wolfgang Scheffler we were introducedto the paper, Solar Tunnel Dryer for FruitSolar Tunnel Dryer for Fruit -- by Albert Esper andby Albert Esper andWerner Muehlbauerfrom the Institute for Agriculture EngineeringWerner Muehlbauer from the Institute for Agriculture Engineeringin the Tropics and Subin the Tropics and Sub--Tropics at the University of HohenheimTropics at the University of Hohenheim(Germany)(Germany).n or er o pro uce pro uc s ree o nsec s, r ropp ngs andust we chose their tunnel dryer.




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Background (continue)l) We changed their design to suit our purpose, but the

basic design criteria we kept, 2m wide and 20m long.e ave u one o ese ryers years ago an are

very much satisfied.m) The dryer has been built in 4 sections and can be

dismantled and transported to any other location.n) One third of the dryer is used as an air heater section

and 2thirds are used for drying.o) The tunnel is covered with standard tunnel plastic UV

pro ec e an as s approx. seasons. e unne canbe opened and closed by 3 people. The tunnel isequipped with 4 fans with a total capacity from 800 -1000m3 per hour, powered by one solar panel 80W.


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Project Fruit Leather

Preparation of fruit

Grinding of fruit

Mixing of fruit pulp

Drying of fruit leather

Storage

Fruit Juice Concentrates Preparation of Dryer

Concentration of juices in the dryer


Fruit Leather

Standard fruit leather in our area is made from a pulpground in a liquidiser type of grinder. Normally this typeof pulp is cooked before drying.

We have changed the recipe by not grinding the fruit butshredding it and not cooking but drying it raw. This helpsto retain the flavour. During the drying process theflavour evaporates first before the water evaporates. Byshredding the fruit we are maintaining small individual

.structure which makes our product more attractive andtasty.

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Preparation of drying moulds We have chosen to make our moulds out of 6mm super

wood (in Germany MDF) with the sizes of 600mm lengthan mm w .

The edge of our moulds have got a 15mm high woodensquare bar. These moulds are light and handy to work.The moulds are lined with a thin layer of plastic (45micron) which is strong enough that it can be removedeasily from the finished product without tearing it.

For one dryer you should have at least 2 sets of moulds.

section (full length) the dryer will take 120 moulds thatmeans you require 240 moulds. When weatherconditions permit (high ambient temperatures like 35 C),we do not use the air heater section.


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Preparation of fruit The fruit is of good quality, fresh and firm.

The fruit is sorted and washed earl in the mornin It isgood to start when it is still dark, because you need to finishthe whole process of cutting the fruit and packing the dryerbefore 11am, that you have 2/3 of a day for the first dryingprocess.

The quality of your finished product is best when you canload the dryer early in the morning. Then the fruit has nochance to deteriorate.

30 40% of our excess moisture should evaporates on thefirst day otherwise the product is loosing on colour andtexture.

It is important that you have at least 2 days of full sunshineto create a good product. The final drying process can be insemi cloudy weather.


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Grinding of fruit

We shred our fruit with normal household shredderswhich work on a batch system with other words we aregrinding approx. 800gr. of fruit into a container then stopthe machine, empty the container and start again.

We have found that industrial shredders which workcontinuously into a big bucket are extremely expensiveand the output does not justify the extra cost. We usethese household machines for 1 - 2 years before we

.production without a big capital layout.

For our production we use 3-4 machines simultaneously.




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Mixing of fruit pulp

The shredded fruit is now immediately mixed with apreservative (sulphur dioxide powder) to prevent oxidation

. The preservative quantity is kept to a minimum to prevent the

destruction of the fruit until is dry.

After drying the sugar and the low water content will preservethe fruit. The quantity of the preservative is so low, that most of the

people do not realise that it has been used. The quantity ofpreservative depends on the type of fruit which you want tory.

After adding the preservative you have a little time as thetexture of the fruit is not deteriorating anymore.

Add only sugar just before you are spreading the mixture intothe mould then the sugar has no time to extract moisture fromthe fruit before it is poured into the moulds.




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Drying of fruit leather The fruit-sugar mixture is measured volumetric into the plastic lined moulds and

spreaded evenly with a plastic spatula. It is important that the fruit-sugar mixture is accurately measured and spread for

consistency. Uneven spread fruit give unequal drying time and create problems when weighing

and packing. The drying time is approx. 3 days, depending on weather conditions.

We have temperatures from 35 C to 44 C in our area in South Africa during normalsummer conditions. We do not need the air heater section in summer and fill the dryer completely to avoid

too high temperatures. High temperatures (above 55 C) destroy the flavour of the product. After the drying process the moulds are taken out of the dryer and stored in an airy

room cr ss-cross w se. The moisture of the product has to be equalised (in the beginning the surface of the

product is the most dry). After a day we check all moulds dryness - moulds are returned to the dryer to finish

the drying process if not completed. One drying mould will be loaded with an average mixture of 0.47kg sugar and 2.21kg

fruit pulp which gives a total of 2.68kg. The finished product weighs 0.92kg




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Storage The finished dried product is taken to a concealed chamber where

the product is exposed to a gas (Phostoxin), it has an active

in case of contamination during the drying process. We pack 6 layers of the fruit leather with the original liner plastic still

attached to the leather on top of each other and wrap this packagein plastic and seal it properly with tape.

Make sure that the packing from the fumigator to the cold store goeswithin a few hours that there is no more contamination possible.

All products which are not packed/sold immediately are stored in acool room at temperatures between 12 C and 14 C.

Our finished products are packed into rolls or in flat sheets or smallsnips. Part of our products are cut to size and covered in chocolate or

yoghurt and sold as a delicatessen - this is keeping our people busyduring the rest of the year.


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Fruit Juice Concentrates

We have in South Africa a special grape whichoriginates from the Muscadel family, we call these

rapes anepoo . These grapes have a special strong muscadel

flavour and are used mainly for table grapes of for

drying to raisins. In past times the juice of these grapes was

concentrated by cooking until it had a honey likeconsistency. Naturally most of the flavour was lost.

retains most of the flavour and vitamins.

We also make concentrates from other fruit juiceslike quince jelly (diabetics purchase mostly).

Small quantities are produced, but it is a beginning.




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Preparation of Dryer The dryer has to be absolutely flat, as

you can guess o erw se e qu wrun to one side.

In order to minimise this problem weuse similar moulds as for the leather,exce t that the rim for the moulds haveto be higher (35mm high).


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Concentration of juices in thedryer

In order to prevent fermentation, the fruit juice has tobe sterilised and is poured hot into the lined mouldso a ep o - mm.

40 to 50% of the water content is evaporated on thefirst day. Thereafter the evaporation slows down

until the final stage of the concentrate is reached. Some of the concentrate can be used as a jam; some

like the quince jelly becomes leather. We have not fully utilised all the possibilities which

,time.

Important is to utilise valuable fruit juice whichotherwise would have been wasted. The concentratecan be stored and used later as required.




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Conclusion

Solar Tunnel Dryers are ideally suitable to preserve fruitwhich would otherwise perish by producing fruit leathersand fruit juice concentrates.

These two products can conveniently be stored andtransported as needed. Fruit leather has got a verypopular market and can be profitably sold. Fruit leatheralso can be transformed further into a more valuableproduct by using chocolate or yoghurt coating.

it is proven, that this can be developed in-expensive andeconomically viable.




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