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  • bobdowser commented on velacreations's instructable Solar Food Dryer2 years ago
    Solar Food Dryer

    East Texas is where our humidity comes from! We got the remnants of a dead hurricane from there back in August of 2007 that parked here for two days and dropped 44 inches of rain (2 summer's worth) in 36 hours.

    You need added heat to draw moisture from the food. You can get that by heating air and moving it around food through convection, forced or passive. And you can do so by direct or indirect radiant heating of the food itself. Either way, the food heats and moisture moves from the food to the air. Try a real-world experiment and build a few different dryers. The unit pictured isn't the best one out there and it's not the worst either. Obviously a dryer isn't intended as a cooker. Temperatures should be limited. And most designs can be quickly and easily modified to match the food, its thickness, the weather conditions, and the ambient temp by using various densities of shade cloth over the collector area to damp down excessive heating on clear, hot days while drying thin, easy-to-dry food...

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    You need added heat to draw moisture from the food. You can get that by heating air and moving it around food through convection, forced or passive. And you can do so by direct or indirect radiant heating of the food itself. Either way, the food heats and moisture moves from the food to the air. Try a real-world experiment and build a few different dryers. The unit pictured isn't the best one out there and it's not the worst either. Obviously a dryer isn't intended as a cooker. Temperatures should be limited. And most designs can be quickly and easily modified to match the food, its thickness, the weather conditions, and the ambient temp by using various densities of shade cloth over the collector area to damp down excessive heating on clear, hot days while drying thin, easy-to-dry foods. But first the dryer must generate enough heat for more marginal drying days. Because on cloudier days, drying thicker slices of wet foods, you'll end up with a stinking moldy mess in a box dryer. I ran into that with several designs back in the 80s before we designed the indirect radiant dryer. And even with a hotter dryer, in the past 30+ years we've had to use our wood-fired sauna as a dryer a few times on days when the weather forecasters just got it completely wrong!

    I think you'll find that your food indeed does get heated. But the more densely you stack your trays the less sunlight the collector "sees". Ideally a dryer would be equally efficient no matter the loading, but that seldom occurs in practice. In our flat radiant design the trays can be loaded densely edge-to-edge as long as the food is one layer thick. Drying is about getting food dry in an efficient manner, before it rots in place. The amount of heat, where it is generated, how much is generated, how it can be regulated for different situations, and how it gets removed seem to be the roots of our disagreement on design.

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  • A Radiant Solar Food Dehydrator that doesn't fight physics - GeoPathfinder.com

    I'm not precisely sure what you mean by "pre-dry". When drying foods, no matter which sort of dehydrator is used, some foods require steam blanching to inactivate enzymes that would otherwise continue their post-harvest conversion of sugar to starch. These include sweet corn, peas, broccoli, cauliflower, green beans, and asparagus. If you don't blanch them they end up tasting like cardboard. Some really wet, thick foods dry better if you either "gut" them (removing seeds and liquid from tomatoes by squeezing them and laying them "skin" side down on the screens, so they won't stick), or simply squash them flat, drain their liquid, and dry them on a stainless steel cookie sheet to make "leathers" (raspberries, strawberries, etc.). This and many othe...

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    I'm not precisely sure what you mean by "pre-dry". When drying foods, no matter which sort of dehydrator is used, some foods require steam blanching to inactivate enzymes that would otherwise continue their post-harvest conversion of sugar to starch. These include sweet corn, peas, broccoli, cauliflower, green beans, and asparagus. If you don't blanch them they end up tasting like cardboard. Some really wet, thick foods dry better if you either "gut" them (removing seeds and liquid from tomatoes by squeezing them and laying them "skin" side down on the screens, so they won't stick), or simply squash them flat, drain their liquid, and dry them on a stainless steel cookie sheet to make "leathers" (raspberries, strawberries, etc.). This and many other "tricks" to make drying easier, whether solar or not, are covered in our book, "Feeding Ourselves - The Four-Season Pantry from Plant to Plate". A download link can be found at http://payhip.com/b/Nk1e .

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