Food Drying and Preservation in a Greenhouse Solar Dehydrator

Food Drying and Preservation in a Greenhouse Solar Dehydrator

Summary

This year was a successful introduction to building and utilizing our first solar dehydration unit, and posed as many challenges as rewards. Our spring began with the construction of our first dehydration model, which was met with some minor structural issues we had to address early on. Our original model included smaller fans, which did not allow for adequate airflow in drying our produce. Once our small fans were replaced with bigger box fans and ventillation screens, we found our revised model worked very successfully. Once all of the structural components were secured and streamlined, our drying season began without a hitch. Despite the unseasonably cool and cloudy summer, we were able to dry and market our goods successfully over the peak summer season and sold all of the items we were able to produce. We found certain things that dried flawlessly at the 130 degree temperatures we were able to reach and maintain, while other produce was considerably more challenging to dry to adequate levels. Our learnings from this season have left much to explore in the upcoming year, including how the concurrent use of a second dehydration unit will impact drying levels and scales of production.

Objectives/Performance Targets

We had a few primary objectives while embarking on this project:

1) To build a successful, easily replicable dehydrator model that is cost-effective and safe for commercial use. Our first dehyrator (40" x 41" x 48") cost us about $1,400 to assemble, using smooth, easily washable materials (aluminum sheeting for the walls), circulation fans, and stainless steel drying screens (cost does not include labor or tools). This dehydrator was an adequate model to protect our dried goods from dust and critters, and typically added 10 degrees to the drying environment from the natural greenhouse heat. We addressed specific safety concerns with our Senior Food Specialist at MDARD, which included having appropriate cleaning equipment for the screens, having a washable, non-absorbent laminate material on the floor where the dehydration is occuring, and using appropriate transportation equipment from liscensed kitchen to greenhouse.

2) To dry a variety of produce items to adequate moisture levels that translate into value-added products. This year's growing season allowed us to focus primarily on a few select crops, and experiment with a variety of others on a lesser scale. In particular, we had an abundance of kale, wild leeks, potatoes, zucchini, hops and rhubarb. Our tomato and melon crops were highly anticipated for sun-drying, but this year made an inadequte showing. Kale was our #1 success, drying to a crisp texture easily within a day, even with added flavorings on it to make them into "kale chips". The bulbs of wild leeks dried easily when shredded or sliced finely, and rehydrated nicely in water for soup blends. Considerably more challenging to dry were the potatoes and zucchini, both containing high water levels requiring high temperatures for longer periods of time to extract the water, and are apt to brown instead of crisp. Rhubarb, while successfully turned into delicious candied gummies with the addition of sugar, was considerably harder to streamline and will be further explored this upcoming year. We are looking forward to another year of honing in on our learnings and drying processes.

3) To determine the appropriate factors needed to replicate consistent drying scenarios for these food items. This was a distinct challenge for us, as any project is that relies entirely on the weather. We discovered our most successful days of drying were the 65-70 degree mostly sunny days unhindered by cloud cover. In peak summer, we were able to achieve 120 degrees inside the greenhouse by 10-11 am, which equated to about 6-8 full hours for the successful drying of kale chips. Moisture content was managed by slightly opening and closing the front or back doors of the greenhouse during peak sun to allow for additional airflow, and this allowed the temperatures to remain high while releasing some of the moisture build.

4) To market the dried products to our consumer base, determine price-points and evaluate profitability. As stated before, dried "kale chips" were our primary success in our markets. We were able to dry 40 1.5oz containers of kale chips from one day's drying in our unit, with 4 hours labor, grossing $200 per batch. Our product proved very popular at local farmer's markets, in our farm store, and at a local music festival we attended. Our dried soup blends never made it to the market this year, but we hope to work more with this and dried herb blends in the upcoming season.

Accomplishments/Milestones

As stated previously, our successes were many over the course of the season. We were able to build a fully functional and sanitary model to use for commercial drying which addressed some of the safety-related concerns of our local MDARD advisor. We successfully dried enough kale chips to generate $2500 of sales income over the course of 3 months, selling out entirely by the end of the summer season. We believe to have built a model that is fairly easy to maintain, replicate, and use in conjunction with other units to increase productivity, while still requiring minimal energy to operate. We evaluated our opportunities for many value-added products throughout the season and, while it is a process that takes time to develop, streamline, and manage thoroughly, the solar-dehydrating process holds much promise for upcoming seasons.

Impacts and Contributions/Outcomes

Social Impact
This year we were able to reach out to 12 student interns who learned about and helped us through our solar-dehydration project. Our work was shared with hundreds of local residents, university professors, season extension agents, and generated a strong interest among fellow farmers looking to diversify their farms.

Economic Impact
Our economic impacts include generating approximately 1 part-time seasonal position that has the potential to pay for itself after the first year. We generated $2500 in sales from our various markets.

Environmental Impact
We spent a season "rescuing" and "repurposing" food grown to excess that otherwise wouldn't have made it to market, utilizing minimal energy inputs (the only external energy source were with fans).