# advice sought - solar dehydrator trays



## cowboy joe (Sep 14, 2003)

Started work on a solar dehydrator this weekend in hopes of using it to dry some of the fruit we harvest this year. I worked out the design last winter based upon work done at Appalachian State University (see the link to the article at Gary's site under food drying - http://www.builditsolar.com/Projects/Cooking/cooking.htm#Drying) The unit I'm building roughly 1/2 the size of the unit in the article. 

Here's were I need suggestions. Stainless steel mesh for the trays will run me over $100. I'm not willing to make this kind of investment without knowing how well the dehyrator will work, especially since the design is unproven. So far I have $0 into the project as I'm using materials from my scrap pile. Vinyl or metal screening is not an option as I'm not certain that I'm comfortable having such materials in contact with food...vinyl is definately out but aluminum might be OK as some cookware is made from this.

My original though was to attach cheese cloth to the wooden tray frames. I think the cheese cloth would be thin enough to allow drying without holding moisture. Then I thought about cleaning...how could I clean the cheese cloth without taking the material out of the frame. I suppose the cheese cloth could be hand washed and then dried in the sun. Not a long term solution but I might be able to get a season or two out of the cloth before it had to be replaced.

Option two was came to me the other day as I was changing sheets on the bed...pillow covers over the frames which could be taken off and tossed in the washer. Just not certain if they would hold too much moisture which might delay the dehydration process and cause mold / rot. Plus the extra layer of fabric might inhibit air flow which is not good.

Option three involves sewing which leaves me out but the thought is something along the lines of a shower cap or toilet seat cover (sorry for the analogy) with an elastic band so the material stretches over the frame...I like the concept as the cover will be easy to remove & clean. Plus, unlike the pillow cover which has a top & bottom which may block air flow, this is only single layer of fabric. The down side is the elastic will eventually dry out from the heat in the box.

The drying box is almost done except for the trays & I hope to add insulation and a reflective surface to the bottom of the chimney by the end of the week. Any thoughts on materials for the trays would be sincerely appreciated. Thanks in advance.


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## nerdrebecca (May 20, 2009)

velcro fabric to frame or place grommets in fabric and hook onto nails on the frame


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## TnAndy (Sep 15, 2005)

Don't know how the airflow in your dryer works, but a lot of them depend on air moving thru the screens. If you put any kind of cloth on there, you may block the airflow and end up with mold instead of dehydration.

Look around cooking/hardware stores for stainless cookie/pie cooling racks, then build the box to fit the racks....they aren't that expensive.


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## WisJim (Jan 14, 2004)

We spent the money and use stainless steel screens. There is a company making and selling food dehydrators that also sells a plastic screen that they say is suitable for food dryers. http://www.dryit.com/ go to "accessories" then click on 
"Looking for food-safe screening? Click here! " I can't seem to make a direct link work.

We have used the Geopathfinder design for many years-- http://www.geopathfinder.com/9473.html after trying other solar dryer designs with poor results.


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## wy_white_wolf (Oct 14, 2004)

Could you use stainless steel window screen? Might be a little hard to find as most have gone to plastic but I think it would be affordable. instead of wood frames you could even build window screens ths right size to fit the dehydrator.


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## Windy in Kansas (Jun 16, 2002)

I think that aluminum cookware is anodized whereas aluminum screening would not be.

As another alternative cloth you might consider sheer drapes. They are fine meshed which would help resist sticking foods and easily pass air through. 

You wrote about vinyl screening---have you considered nylon? Most hardware stores supply it.


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## cowboy joe (Sep 14, 2003)

The window sheers along with the grommets / velco are interesting thoughts. The cookie racks are a great idea for the bigger items but we'll also need a smaller grid for items such as cranberries. 

The anodizing would explain the difference between the screening and cookware. I looked for screening at the local stores and only came up with fiberglass & aluminum so I'll look on the internet for alternatives such as stainless.

Looks as if I have my work cut out for me experimentation wise. We make sushi & youngest DD came up with the idea of stringing sushi mats (bamboo) across the frames. Inexpensive, durable, & food safe...she gets a big hug for thinking outside the box...not that I need a reason to give her a hug. Might even be able to use these on top of say a cookie rack when we dry smaller items. Lots to think about. Thanks everyone!

BTW, the design uses a drying box on top of a chimney. A second article was published in home power by students looking to improve the original design. The students actually built the units and performed various modifications, then tested their theories under controlled condition. Included are revisions such as the effects of a reflective bottom surface, absorber types, number of layers of glass and a few others. Makes for an interesting read for those who like the technical aspects.


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## MELOC (Sep 26, 2005)

i eat at subway quite a bit and i notice they use some sort of mesh to place food in the oven for toasting. it appears to be a plastic. i wonder if they have any info on what they use?


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## RVcook (Mar 29, 2008)

When DH built a freestanding unit years ago, we too were trying to find inexpensive items to use for screening. We finally decided on a nylon mesh, stapled to the rack frame. It worked quite well, but we found that there were definitely issues with sagging. To remedy this, DH took some butcher's string and criss-crossed it underneath the fabric. It helped, but didn't totally solve the sagging problem.

If we were to do it again, I'd probably go with TNAndy's idea of using mesh cooling racks. That would also eliminate the need to build the racks themselves which would hold the screening material. For smaller items, I'd just place a piece of sheer nylon curtain fabric over the cooling racks. If you decide to go with "sheers", make absolutely sure that they're nylon and NOT fiberglass. 

RVcook


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## mightybooboo (Feb 10, 2004)

My trays use a plastic/fiberglas? screen,works real well.


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## cowboy joe (Sep 14, 2003)

Decided to go with food grade cheesecloth for the test runs (<$5 total for the amount I need)...I know the lifespan will be limited but no sense knocking myself out or spending big bucks on an untested prototype. I can always upgrade to a better solution once I know the dehydrator works.

Added the styrofoam insulation to the chimney last night and built the frame for the bug screen which fits at the bottom. Ran out of aluminum foil for the reflectors so I'll have to pick some up. This will be the first item I've had to buy. Still at the $0 investment level for the project (other than time). Figure I'll have less than $20 total invested once I pick up the material for the absorber. 

I was going to post pics but my camera won't turn on...such is life. I'll post updates now & again if anyone is interested. Thanks again for the suggestions.


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## mightybooboo (Feb 10, 2004)

Thanks Joe for sharing and good luck.I look forward to your test results.


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## cowboy joe (Sep 14, 2003)

Busy weekend. Finish construction of the dehydrator including the trays. The cheesecloth was a bit harder to work with than originally thought but it worked out OK as I had cut strips of wood to go over the top of the cloth once it was stapled to the tray. Something tells me this is a short term solution as the cheesecloth tears very easily.

So, I get the pieces together (the drying box, chimney come apart & the window comes out for storage / moving / cleaning), put the box outside, watch the temp climbs 20F in only a few minutes...then the sun goes in. That was the last I saw of the sun for the rest of the weekend...sigh. :grit: Looks like a nice weekend on the way so I hope to get the dehydrator tested then. Looks promising so far.


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## cowboy joe (Sep 14, 2003)

Quick update...the solar dehydrator worker better than expected. The unit was able to hold +50-60F temp rise while the sun was out with reasonable (even though unable to measure) air flow. Dried bananas, zucchini, & tried a few cranberries even though they are still not ready, mainly as an experiment.

The cheese cloth works OK even though the bananas stuck. I adjusted the vents for ~115F for the bananas. They were OK but kind of rubbery. Think I'll use a higher temp next time around. The 1/8" zucchini slices turned out like potato chips only better and the cranberries dried like raisins. Looking forward to trying other fruits & vegis. Thanks to everyone for the feedback.


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## mightybooboo (Feb 10, 2004)

Nice job CJ.
You want your banana chips hard.


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## gwest (Oct 9, 2008)

TnAndy said:


> Don't know how the airflow in your dryer works, but a lot of them depend on air moving thru the screens. If you put any kind of cloth on there, you may block the airflow and end up with mold instead of dehydration.
> 
> Look around cooking/hardware stores for stainless cookie/pie cooling racks, then build the box to fit the racks....they aren't that expensive.


Anyone ever try recycled polyester felt, it's plastic, air flows through it freely and it sticks to velcro like mad. It holds up to some heat also. I've used it as absober material in solar air heaters. Works good


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## Pritch (Feb 21, 2009)

I saw the guy from the TV show "Good Eats" make a dehydrator using disposable paper furnace filters and a box fan. Perhaps these filters would work for you.


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## Windy in Kansas (Jun 16, 2002)

Some of the furnace filters appear to be fiberglass strands---be mighty careful and know what you are using.


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