Solar Food Preservation

I briefly mentioned my solar dehydrator project in a previous post. Now that this project has been wrapped up, here's a little more detail.

Having lived most of my life in temperate climates, I'm used to the idea of seasonal fruits and veggies, and the need to preserve produce in order to have something tasty to eat in the winter. Sure, NAFTA eliminates some of that need, but preserving food is still an important part of American culture.

During the first few months in Ecuador, I quickly realized that food preservation is very rare here. Before refrigeration was widely available, meat and fish were smoked or dried to extend the bounty of a hunt for up to a month. Now, even if a family doesn't own a fridge, the store down the street that sells chicken probably does. So few people preserve meat anymore.

Although food preservation isn't common, there are some products that need to be dried as part of the processing. Cacao, coffee, and plantain (for grinding into flour) are the most common.

At the school farm, the teachers were experimenting with designs to accelerate the drying of cacao and improve the quality (mold and flies are very common when sun-drying cacao).

Version 1.0 of the solar dehydrator.

The first design they came up with had a lot of good qualities:
-Made from recycled/free materials
-Improved airflow below cacao compared with sun-drying on a tarp
-Easy to use


However, there's nothing keeping flies away, and you can see there is still a problem with mold. For an improved design, we needed to meet the following characteristics
-No way for flying or crawling insects to access food
-Movable, to take advantage of morning and afternoon sun
-Built from recycled/cheap, locally available materials
-Food can be left in over night (we expected food to take at least 2 days of bright sun to fully dry)
I found a design for a solar dehydrator that was intended for use in northern Minnesota, with similar humidity to Santa Clara. With a few modifications, here's the result.

Ricardo laying the air-flow-channel layer onto the base.

Isaac adding the filled food frames

Kirstie with the solar heat collector

Version 2.0, complete with glass top

This design worked better than I hoped. In one attempt, we dried plantain in two days - a process which normally takes two weeks using traditional methods. Having confirmed the design's potential for drying cacao, coffee, and plantain, we branched out into fruits. On a good hot day, we dried some sweet bananas in just one day.

Mmm, look at that crystalized natural sugar on some of the bananas!

Papaya that got a little TOO hot while drying.

While experimenting with different foods, I wanted to tweak some aspects of the design. The cheesecloth used for supporting the food was the most expensive part of the design, so we tried making a frame with bamboo slats instead.

Isaac and Carlos working on version 2.1

We decided the bamboo frames weren't a good idea after the first night, when we found evidence of cockroach nibblings on the food.

At this point, we decided the project was interesting enough to merit getting the students involved. I worked with the students to assess how version 2.0 could be improved in order to better meet the needs of the farm. They suggested we make it bigger, with a higher base (to eliminate the need to bend over while filling it). Then we got started building.

We realized that a higher base would make the unit heavy enough that rotating it 180 degrees for the afternoon sun would be difficult. After hunting around, we found some old drafting tables with a tilting mechanism that worked great for bases.

Version 2.2

We used the corrugated plastic for the top layer in the final version after the students broke two glass sheets handling the dehydrator.

In the end, the project was only a partial success. Although larger and seemingly more complex, version 2.2 just didn't get as hot as 2.1 did. I attribute this difference primarily to the corrugated plastic top in version 2.2.

However, the students and teachers all learned a lot about the iterative design process, and we ended up with a device that, although far from perfect, accomplished the original goals of allowing rapid drying of cacao and plantain without giving insects access to the food.

Additionally, we all grew a lot closer as a result of the project. Being used to an educational system where teachers often tell students exactly what to do and how to do it, the students enjoyed the opportunity to work alongside myself and their teachers, and appreciated having their ideas considered and implemented.

..Isaac..


This post is part of the Peace Corps Projects and Rethinking High Tech series.