Introduction: Simple Solar Fruit Drier. Will It Work?

I have a few prune plums slowly turning into prunes on the ground so thought I would make a solar drier to slightly enhance the drying.  So it is just white shade cloth above and black landscape fabric below and about 2 inches (5 cm air gap).   The air and moisture from plums should easily pass through either the black fabric or white fabric. and the plums do get hot underneath the white shade cloth.  Please try it.  I recommend keeping the black landscape fabric no matter what and try different covers.  Maybe, glass, or plastic or mosquito net.  The idea is to make solar drying as cheap and "dumbed down" as possible so that even a guy like me can do it. on a big scale.  Big scale is really important.  Thousands of tonnes of fruit rot on the ground every year.   I also want to dry apple slices . Hopefully the cloth will keep out bugs.

Comments

gaiatechnician (author)2012-11-18

We had a glorious dry September and the prunes turned out really nice. They are about halfway between the taste of real prunes and raisins. My wife makes cookies from them and they are similar to date cookies. I think the key was that September was so much drier than usual so nothing got mouldy. Next year i will try using calcium chloride to maintain the really dry environment that we need. Thanks for inputs Brian

rimar2000 (author)2012-09-18

I think you could enhance your design adding a refflective layer under the black plastic coat.  Like this http://www.aislantestermicosrt.com.ar/aislantes/termicosg.jpg or this http://tecnoaislantes.com.ar/files/images/thermoespumaenc.jpg
Also you could add a base of spanded metal like this: http://www.sadimetal.com/contenido/PROD4ac0f8c9a0828.jpg
in order to allow the air flow around the fruit. The metal could be raised one inch or so over the black ground.

gaiatechnician (author)rimar20002012-09-18

Thanks Rimar, I think either would be helpful but the reflective stuff might restrict airlfow.? I think the expanded metal would work instead of chicken wire underneath the landscape fabric.. (I messed up because I used "plastic chicken wire" and it is too stretchy). Mine is at a little angle and the plums tend to roll downhill. I will look for chicken wire that has holes a the size of or slightly bigger than plums. That way there will be little "dents" that the plums might sit in and I might be able to angle the whole thing a little to the south.
It is a kind of fun "how cheap can you go" experiment.
People keep saying plums need really hot and quick to dehydrate but maybe not if the skin stays on? Then the skin protects against mold and lets the moisture out slowly.
Also, dew in the morning on the plums? You would think it is bad but maybe it sucks water out through the plum skin? Or maybe it is water that came out of the plum overnight? There may even be something going on like what happens in ice wine? Anyways, seems to be working, Not fast but cheaper than 10 dehydrators.

rimar2000 (author)gaiatechnician2012-09-19

Really I am not experienced in the subject, I just do my guesses. Every year I say "would have to make a fruit dehydrator" but so far I've been on intent. What I read is that we must be careful not to exceed a certain temperature because there are fruits that are "burned".

Expanded metal come in many sizes, and is cheaper than chicken wire. The advantage of this last is you can found it in any neighborhood hardware stores, while the "standard" expanded metal you can find is only the most common size, that used by plasterers for ceilings.

gaiatechnician (author)rimar20002012-09-19

Thanks, Yes it is guesswork for me too. I try to leave as much room in my gigantic "solar drier" as I can for various options. It is about 1 meter by 3 meters in size.
I think with all the "cloth" under and over the plums moisture will quickly evaporate and keep thing cooler.
I have heard that sometimes in the more professional solar driers, the airflow actually stalls because so much moisture is evaporating and it cannot go up anymore because moist air is heavy air! So with this, the air can go wherever it wants to go! Up or down
It is great that you are making suggestions. I really appreciate it.
Brian

rimar2000 (author)gaiatechnician2012-09-19

ERROR ERROR ERROR...! Humid air is NOT heavier air.

Although it seems ridiculous, water vapor is lighter than air. Then, when air and steam are mixed, the result is lighter than dry air.

From wikipedia: (http://en.wikipedia.org/wiki/Density_of_air)

"Water vapor
The addition of water vapor to air (making the air humid) reduces the density of the air, which may at first appear counter-intuitive."

gaiatechnician (author)rimar20002012-09-19

Hi, Rimar, ok. But they still have documented some problems where they got something wrong and drying was not a success. It is September now and the days are sure getting shorter here. It still gets hot and it is drier than usual but the time when the plums are getting the full sun is greatly diminished from even a week ago.
Brian

gaiatechnician (author)2012-09-19

Several really short videos about the project are going up right now. It does seem to be working. http://www.youtube.com/playlist?list=PLkzXlmAwZTZc8doLlRF_ZGZ03gImBuvGC&feature=view_all

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Bio: I am a stone mason. My hobby is making new solar cooking and gardening stuff. I have used solar heat to cook soil for a ... More »
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