Food Drying and Preservation in a Greenhouse Solar Dehydrator

Final Report for FNC13-933

Project Type: Farmer/Rancher
Funds awarded in 2013: $7,476.29
Projected End Date: 12/31/2015
Region: North Central
State: Michigan
Project Coordinator:
Patrick Scharinger
Pond Hill Farm
Kelly Doyle
Pond Hill Farm
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Project Information



Pond Hill Farm is a family owned and operated farm and agri-tourism destination for local residents and traveling tourists, open year-round. The farm grows approximately 30 acres of produce on its total 157 acres of land, selling the harvest daily in its on-site farm market, in its seasonal Garden Café, at 4 local weekly farmer’s markets, and wholesaling to a number of local distributors. Our fresh produce includes kale, broccoli, carrots, onions, tomatoes, lettuce greens, cucumbers, squash, etc. We also have a rapidly growing line of canned goods produced at our on-site licensed canning facility, as well as a 3-acre vineyard growing grapes for our own wines for sale in our tasting room. We grow vegetables year-round with the help of our two heated greenhouses, two low tunnels, and hoop-house (awarded though a research grant through the C.S. Mott Group at Michigan State University).


Pond Hill Farm has strived for economic and environmental sustainability since its inception. By diversifying our markets (selling wholesale, at farmer’s markets, through our farm store and on-site café), diversifying our crops (various fruits, vegetables, flowers and hops) and diversifying our business (farm/ café/ winery/ cannery/ spring flowers/ store/ events location) we are able to sustain ourselves economically. Environmentally, we rotate our crops every year, plant cover crops to enhance our soil, spread manure, collect food scraps from our café and excess food grown to feed our animals, recycle all possible materials to minimize on-farm waste.


GOALS: There are 3 main problems that our project set out to address:

  • Having local food products year-round in a region with a relatively short growing season
  • Finding a profitable use for surplus and/or blemished produce
  • Inefficient utilization of greenhouse space during summer months.

Our goal was to mitigate these problems by building a solar dehydrator to use in our greenhouse space that could produce a shelf-stable product using excess produce, utilizing the greenhouse in peak heat of summer season. We hoped to build a model that was easily replicable and had the capacity to produce shelf-stable product on a scale large enough to warrant economic impact.


We built our initial dehydrator (40” x 41” x 48”) using smooth easily washable materials (aluminum sheeting for the walls and stainless steel drying screens) as to comply with health officials request (the screens needed to be of a size to fit into our industrial dish washer to sanitize, and the dehydrator needed to protect from outside critters and dust). Our concept was to build a unit that could easily be used in conjunction with other units in order to scale up our processes and dry more produce at once. Our initial model included small circulation fans to promote airflow, but we soon realized that the small fans were not sufficient and updated to larger box fans on one side with a mesh screening to keep particles and critters from getting in. The sides of our dehydrator had doors that opened from each side so that we could easily remove our screens from each side. When we built our second unit, we removed the wall furthest from our fans on the first unit and joined it onto the end.


Our process of preparing food generally included using our commercial kitchen to cut or wash the produce, add seasonings or spices for flavoring, and then pack into food-safe containers for transport to our greenhouse. We experimented with drying of many things that we grow on our farm. We focused on the crops we tend to have a surplus of, including kale, wild leeks, potatoes, zucchini, hops, melons, tomatoes and rhubarb. Sundried 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 and onions dried easily when shredded or sliced finely, and rehydrated nicely in water for soup blends. Considerably more challenging to dry were the potatoes, zucchini, and tomatoes, containing high water levels and therefore requiring high temperatures for longer periods of time to extract the water, and they 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 was fairly inconsistent.

Considering our greenhouse’s placement to the sun, we generally prepped our food first thing in the morning and loaded our dehydrators around 10 am as it started to warm up. Around mid-day, our greenhouse would achieve over 100 degree temperatures (while our dehydrator would often reach about 130 degrees) but the build-up of the moisture within the greenhouse would pose a problem for drying, so we found it beneficial to manually open the end doors to allow for more airflow and release the condensation. By around 5:30 or 6:00 the temperatures would begin to drop which is when we prepared ourselves to pull our product, or check for doneness. If the product looked, felt, and tasted done, we would then pull our product and put it into tubs to be transported and stored where they could condition overnight and be checked the next morning to see if they maintained their dryness. At the end of the process we also transported our drying screens to the dishwasher, and cleaned the dehydrator with sanitizer, and prepared for packaging.


We involved several people in the consultation of this project. Included was Wendy Wieland of our local season extension agency who helped us connect with some folks to promote and educate about our project. We connected with our MDARD (Michigan Department of Agriculture and Regional Development) official, Tim Treadway, to get assistance in answering our questions of food safety as we developed our dehydrator concepts. We worked with the head chef and sous chef of The Garden Café for culinary expertise when developing ideas for flavorings and with technical questions about water activity levels, drying, and food safe handling. We involved with this project, 24 student interns, both of college and post-college level education, who were able to participate with our food preparation, harvest and marketing, in addition to contributing ideas that we hadn’t considered to further our project ideas. Our project was also shared with an “After-Hours” event we hosted for the Harbor Springs Chamber of Commerce.


Of all of the items that we dried, we were most successful drying and marketing kale as “kale chips”, as there was less water activity than most of the other items we dried, as we always seemed to have a surplus of kale, and as our markets were particularly interested in this newer trendy food item. In our first year, we generated about $2,500 in sales from the product that we were finally able to market (at $5 for 1.2 oz of chips) through various market channels (3 farmers markets, our farm store, and 1 summer folk music festival we cater for). In our second year, we did roughly $1,500 in sales, as our kale crop was less abundant, and as our weather was unseasonably cool and cloudy, and we discovered many challenges with the addition of our second unit. Our other dried products never made it to the marketing stage, as we struggled with drying consistency, time constraints, lower crop yields, and (as stated before) unseasonably cool/ cloudy weather throughout the summer more information about our challenges below).


We encountered many challenges, particularly in our second year, with our project and products that we hadn’t anticipated.

  • Inconsistency in product – In general, we had a lot of difficulty maintaining a consistent product because of how much the project relied on the weather conditions. Because the greenhouse was so weather-dependent, we often found that our product would spoil as a predicted sunny day became overcast, or if the temperatures we expected weren’t achieved both in and outside of the greenhouse. In the future, if there were a backup heating unit to help see a product through, I could imagine a greater feasibility.
  • Moisture buildup in greenhouse – Without manually regulating the airflow by opening and closing greenhouse doors throughout the day, the greenhouse would build up an incredible amount of moisture that kept our product from fully dehydrating.
  • Difficulties with using multiple units – We had more success in drying our produce with one single unit, although we had trouble fully delineating why the two units wouldn’t work as well together. We tinkered with several ways to build more heat and facilitate better airflow inside (including building a little mini greenhouse over our heating unit, adding and subtracting fans, subtracting trays of product, etc.) but ultimately we just struggled to find a consistent way to dry everything inside the two conjoined units.
  • Time constraints – Perhaps the biggest challenge to this project were issues with time constraints. The time investment in not only harvesting a surplus crop, but washing it, prepping it, transporting the product to the greenhouse, monitoring it, taking it out, conditioning it, packaging it, and cleaning the unit after each batch inevitably didn’t validate the amount of product we were actually able to produce and sell, considering all of the inconsistent product we were generating. Often, all of the prep work would be done only to discover that the forecast had been wrong, and all time and energy spent went to waste. In addition, all of the work that goes into the dehydrator happens during peak summer where farmers already carry the bulk of their workload, so adding this project on top of the other farm responsibilities proved incredibly demanding.


Social Impact:

In 2 years we were able to reach out to 24 student interns (both college and post-college) who learned about and involved themselves in our solar dehydration project. Our work was shared through various markets with hundreds of local residents, university professors, season extension agents, and generated a strong interest among fellow farmers looking to diversify their farms and farm products. We provided information about the dehydrator and our project on our packaging, including where they could learn more about our dehydrator online (we measured around 200 visits to our dehydrator page, some of which was facilitated through our Facebook postings).


Economic Impact:

We generated $2500 in sales from our various markets in our first year; $1,500 in sales in our second. If there had been a way to streamline some of the inconsistencies I imagine that this may have provided 1 part-time seasonal position for someone, were they also fully able to dedicate the time during peak season to focus on the production entirely.


Environmental Impact:

We spent two seasons "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 was box fans).


We conducted a yearly demonstration including 24 student farm interns (college/ post-college) explaining our processes in solar dehydrating, our methods, our process for designing the dehydrator, the food safety concerns involved in the project, and the many successes and challenges we encountered along the way. Many of these interns continued to participate, helping in the preparation and sales of the product, and some of the monitoring and testing of the product.

We shared this product on our Facebook and webpage, tracking around 550 views to our Facebook and around 200 visits to the webpage. We included explanations of our project both on our website and on our actual marketed goods describing the grant and the sustainable benefits of drying in a solar dehydrator.

We were asked to participate in the 2013 Northern Michigan Small Farm Conference but declined because we considered the depth of research we aspired to achieve and hadn’t yet been reached, and that we needed more information before we felt comfortable sharing.

(Pictures attached)



Project Objectives:

Over the course of the year, we plan to measure a variety of components in order to assess this project as a model of sustainability and productivity.

We intend to keep detailed records of temperatures reached and time necessary to dry individual goods, as well as testing our products to assure food safety and measure water activity level, in order to determine what precise environmental factors must exist in order to successfully and safely dehydrate foods and create a shelf-stable product.

To measure the economic benefits of our project, we will track the number of personnel hours needed to maintain operation of the dehydrator, including dehydrator construction hours, time cleaning and processing the produce, as well as packaging and marketing the items. We will track the amount of product and sales dollars to measure against all other expenses along the way to determine certain product’s profit margins, and whether or not our design has the ability to pay itself off in the long or short-term.

We will measure social benefits by tracking participation levels in the workshops and outreach events we participate in, and include evaluations where possible. We will gauge interest levels to our project and products by tracking visits to our website’s dehydrator page.


Participation Summary
Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.