Food dehydrator project

[TAT2D]

I was out googling for home-built food dehydrators. Found several sites offering plans for purchase, and a few sketchy descriptions. Several references to a plan from a guy at OSU as well, but mostly in out-of-print books from Amazon.

Then I found what I was after --

<broken link removed>

"The majority of the text and plans provided here were originally obtained from the Oregon State University Extension Service Circular 855, and were last revised in 1984 by Dale E. Kirk, professor emeritus of agricultural engineering at Oregon State University..."

It looks like a typical up-draft unit, but he deals with the usual problem of the last tray getting wet air (and working more slowly) by tapering the depth of the lower trays to allow more bypass air. This does mean you have to make your own trays, but maybe that's not a bad thing if you'd like to replace them periodically. Also means you can't shuffle the tray positions to balance out drying rates, but perhaps the bypass works as designed.

The other hot set-up, I gather, is buying the loose trays from the Excaliber folks and building your own box around 'em.

MrB

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[DALE]

I built this last year. Works well except for the screen. I did use screen but then bought some dehydrator mesh sheets to lay on the screen. Prevents sticking and the sheets are easier to clean.

http://www.northwestfirearms.com/forum/showthread.php?t=14084&highlight=dehydrator

 

[bersaguy]

I have also built a food dehydrator from the OSU plan, about 35 years ago. It is still going strong after hundreds (or thousands) of pounds of fruit and vegetables through it. It is a great design, but a little bulky by todays standards.

 

[Gunner3456]

Are stupid questions allowed here, LOL?

Our kitchen range has what's called a convection oven. The best I can tell, it simply has small fans in it to keep air circulating rather than the normal static air.

Now, for instance, it will bake three shelves of cookies, all evenly and all getting done at the same time. Our older ovens all needed to have different cookie sheets removed at different times and you had to watch them. Also, all of the cookies on any one sheet weren't necessarily all equally done.

Another thing is that you subtract 1/4 of the cooking time from what the cookbook says. If it says an hour, you set the timer for 45 minutes. Everything comes out even and perfect.

Think of it this way. Suppose you had two ice cubes to melt. You put cold water from your sink faucet in a bowl and drop one cube in it. The other cube you hold under the running water. Of course the one under the running water melts first because the "cold" is being removed from around it at all times, and new water makes contact. I think it's that principle, but with heat instead of cold.

Why couldn't someone put a couple of small circulating fans in that thing to even out the heat and moisture throughout? What would happen?

I'm thinking of something like cheap 4" computer fans and a cheap or used computer power supply to power them. Or... ??

 

[DALE]

Are stupid questions allowed here, LOL?

Our kitchen range has what's called a convection oven. The best I can tell, it simply has small fans in it to keep air circulating rather than the normal static air.

Now, for instance, it will bake three shelves of cookies, all evenly and all getting done at the same time. Our older ovens all needed to have different cookie sheets removed at different times and you had to watch them. Also, all of the cookies on any one sheet weren't necessarily all equally done.

Another thing is that you subtract 1/4 of the cooking time from what the cookbook says. If it says an hour, you set the timer for 45 minutes. Everything comes out even and perfect.

Think of it this way. Suppose you had two ice cubes to melt. You put cold water from your sink faucet in a bowl and drop one cube in it. The other cube you hold under the running water. Of course the one under the running water melts first because the "cold" is being removed from around it at all times, and new water makes contact. I think it's that principle, but with heat instead of cold.

Why couldn't someone put a couple of small circulating fans in that thing to even out the heat and moisture throughout? What would happen?

I'm thinking of something like cheap 4" computer fans and a cheap or used computer power supply to power them. Or... ??

Are you referring to the OSU plans? It has a duct fan that circulates the air.

 

[Gunner3456]

Are you referring to the OSU plans? It has a duct fan that circulates the air.

OK, I'm unable to see exactly how it works. Does it draw in outside air, or just circulate the air in the box as a convection oven does?

Does everything dehydrate evenly, all at the same time? If so, then it's good to go imho.

 

[DALE]

OK, I'm unable to see exactly how it works. Does it draw in outside air, or just circulate the air in the box as a convection oven does?

Does everything dehydrate evenly, all at the same time? If so, then it's good to go imho.

The fan draws in some outside air and recirculates as well. Initially it helps to open the access door slightly to help remove moisture laden air. I close it after a few hours. I would suggest that anyone serious about dehydrating should look at the excaliber or similar model. To build this using new components isn't cheap. I just like building my own stuff, so didn't mind. It is big, heavy and bulky.

 

[bersaguy]

There is an adjustible vent on the door of the dryer that I built from the OSU plans. It is approx. a 4" diameter hole in the door covered by a sheet aluminum cover. You can adjust the airflow.

The heating elements are thermostatically controlled and it include a circulating fan.

 

[Gunner3456]

Sounds like it works great then.

 

[TAT2D]

Hey, all --

Thanks for the link to the earlier thread when this came up, six months ago. I gotta' get better at searching the forums. The idea for the tray sheets from Bi-Mart sounds like a really good idea. I did find the cone-heaters here --

<broken link removed>

Seems like they're awfully fond of 'em, tho'. ~$25 each, tho' likely one could be enough, if you get the right size on the first try... Still, you could go through a bunch of lamps for that price. But you save money trading nine porcelain sockets for one, I suppose. Being an exposed element it would provide a slightly heightened shock and burn hazard.

Dale mentioned in the other thread adding more lamps, as he was only getting 140-deg. How about bumping the 100 W lamps to 150s, if you have the clearance.

I'm wondering what could be done to reduce the bulkiness w/o reducing the capacity. Could the trays sit closer together? Could the volume at heater area at the bottom be reduced, perhaps w/ one of the cone-heaters, laid sideways, and with appropriate heat shields? How about putting all the electrical bits on a tray, so that could be removed for cleaning? How about provision for an over-temp shut-off or a shut-off timer? Maybe I'm over analyzing it...

MrB

 

[slideglider]

I thought I remember reading somewhere that a traditional oven will work if it has the convection option and digital controls to keep the temperature stable in around 150. I think they kept the oven door cracked open with a wedge if I remember right.

 

[Gunner3456]

I thought I remember reading somewhere that a traditional oven will work if it has the convection option and digital controls to keep the temperature stable in around 150. I think they kept the oven door cracked open with a wedge if I remember right.

I don't know about that - interesting. I'd want to calculate the power usage of both. The dehydrator is easy. How many bulbs at how much wattage, and the fan should say...

I do have one of those electrical tools that makes a loop around a wire and reads the power usage. I could do that by accessing the cord. I'd want to incorporate more shelves somehow. There's too much distance between the three factory ones and therefore wasted space for that purpose.

Also, I believe it would heat the house - not a good thing in the summer.

I'm not sure you'd have to crack the door. It does vent itself to prevent steam buildup. The glass door never fogs up.

It sure would be handy to have it right in the kitchen though.

 

[TAT2D]

I'd want to calculate the power usage of both. The dehydrator is easy. How many bulbs at how much wattage, and the fan should say...

Times duty-cycle. The heater isn't running all the time. The fan is almost free, and skewed power-factor at that.

I do have one of those electrical tools that makes a loop around a wire and reads the power usage.

http://www.p3international.com/products/p4460.html

These units are (were?) ~ $27 at Costco. Kinda' fun. Along with everything else, you can plug, say, your refrigerator in through it for a week and it'll show how much your frige is actually using, given start-up surge, duty cycle, etc.

MrB

 

[Gunner3456]

Times duty-cycle. The heater isn't running all the time. The fan is almost free, and skewed power-factor at that.

http://www.p3international.com/products/p4460.html

These units are (were?) ~ $27 at Costco. Kinda' fun. Along with everything else, you can plug, say, your refrigerator in through it for a week and it'll show how much your frige is actually using, given start-up surge, duty cycle, etc.

MrB

Nice deal there from Costco. It wouldn't work on 220, or something which is hard wired, such as a range.

I have something similar to this, which just loops around any wire: Link

 

[TAT2D]

The idea for the tray sheets from Bi-Mart sounds like a really good idea.

Popped into Bi-Mart last night. Found some sturdy looking metal wire screens for $7-8 each; and some plastic screens, 2, plus a DVD and some jerky spice for $15. Think I'm back to plan-A.

MrB

 

[Gunner3456]

OK, so what's the deal on shelf life on dried fruits and veggies, and jerky?

Do you store it with oxygen absorbers, vacuum seal it... ??

How long will it keep and what's the best method?

I googled that and I'm getting tired of google. They let people pay to be first on the list of returns. The first 8 pages had nothing but sites that want to sell dehydrated foods and/or dehydrators.

 

[bersaguy]

OK, so what's the deal on shelf life on dried fruits and veggies, and jerky?

Do you store it with oxygen absorbers, vacuum seal it... ??

How long will it keep and what's the best method?

I googled that and I'm getting tired of google. They let people pay to be first on the list of returns. The first 8 pages had nothing but sites that want to sell dehydrated foods and/or dehydrators.

Dried fruits and veggies are easy to store. We let them cool to room temp and then put them into large glass jars (we use the large size Adams peanut butter jars. They have a wide mouth and hold more than a quart.) The jars of dried goodies get stored in the pantry away from sunlight.

Generally we dry as much as we can and most is consumed by the next harvest. So as to what the max. shelf life is, I really don't know.

The local office of the Extension Service is a good source for info on drying foods.

 

[Gunner3456]

Dried fruits and veggies are easy to store. We let them cool to room temp and then put them into large glass jars (we use the large size Adams peanut butter jars. They have a wide mouth and hold more than a quart.) The jars of dried goodies get stored in the pantry away from sunlight.

Generally we dry as much as we can and most is consumed by the next harvest. So as to what the max. shelf life is, I really don't know.

The local office of the Extension Service is a good source for info on drying foods.

Thanks.

If they'll last from harvest to harvest, that's a good thing to know.