Our SARE Grant funded building and testing two low cost approaches to dehydrating fresh produce, herbs and flowers on our small Maryland farm. We built and compared two food dehydrators, one passive solar design and one using an electric heater and fan. We constructed the two dryers for a fraction of the cost of comparable commercial units and had great success drying a range of products including tomatoes, kale and flowers.
The construction material for both dryers was only $600 combined and the drying capacity and quality of these dryers is comparable to commercial units that sell for between $6,000 and $20,000. We hired a carpenter to build the dryers so we spent a total of $1,600 for construction and building materials. Both our dryers performed well in our tests reducing moisture content up to 93% for tomatoes. We measured our results by weighing our products before and after drying, conducting a taste test and recording our experiences using both types of dryers.
While the two dryers performed very well on many products, we need to refine our production methods and invest in an indoor packing area before we can be licensed to bring our dried food products to market in Maryland. In the meantime, we were able to market dried flowers.
Our grant explored low-tech solutions for dehydrating crops on our farm to help reduce waste and increase farm profit from new value added products. In early 2013, we built two dehydrators to test on our farm. The first model is an outdoor passive solar stack dryer that utilizes the chimney effect to dry products with increased air flow. The second model is an indoor electric cabinet style food dryer.
We built the two dryers in the spring of 2013 and tested them for two farm seasons on a wide variety of crops. We made a few design modifications and developed our drying techniques as we worked. We tested both dryers using greens, tomatoes, flowers, sweet potatoes, eggplant, hot peppers, basil and other herbs. We continued testing and refining though the 2013 and 2014 farm seasons.
We packed our products using a vacuum sealer in plastic and glass. We held tastings in December 2013 to get feedback on six of our dried products: 2 kale chip recipes, dried tomatoes, basil, spearmint and sweet potato chips. We applied the feedback and made some adjustments to both dryers for the 2014 season.
- Building a solar dehydrator (completed Spring 2013, design attached below)
- Building an farm-scale electric dehydrator (completed Spring 2013, design attached below)
- Testing both dryers on the following crops: tomatoes, basil, kale, sweet potatoes, flowers and mint/mixed herbs. Weighing crops before and after drying. (2013 and 2014 farm season)
- Holding a taste test and measuring feedback (completed December 2013)
- Sharing results at conferences and through a Acres USA, a national sustainable agriculture publication (completed winter 2014)
The Solar Dryer
The passive solar model designed by UC Davis Professors James Thompson and Michael Reid utilizes the chimney effect to dry products with increased air flow (see PowerPoint below the Outreach section below for plan). They have helped farmers build and test similar models in California, Thailand and Honduras. They were able to achieve excellent results with this incredibly low-cost and low-tech model for drying products like tomatoes and mangoes. The solar dryer is very simple and can be built for less than $100.
Thompson is optimistic the dryer design offers promising new low-tech solutions for farmers. According to Thompson, “The UC Davis Chimney Dryer is a significant improvement in solar drying technology. It heats the drying air like all solar dryers, but it also moves the air past the product at high speed. A chimney provides the air movement and the drying chamber design squeezes air through a small area so it flows five times faster than a typical cabinet drier.”
Most farms will have the materials on hand to build the solar dryer with the exception of the drying trays. The plans include making a 100-foot x 2-foot soil berm that is covered in plastic. We used our raised bed maker and adjusted the berm by hand. The chimney is a 2-square-foot x 6-foot tall wood frame that is also covered in plastic with openings at the top and bottom. The drying trays are laid on some wood framing that is placed on the plastic covered berm and covered with a second layer of plastic sheeting. In our second year, we modified this dryer by lifting the drying surface up on a table like platform instead of using the soil berm.
The solar dryer performed very well during our first tests in June and July. We were able to dry greens and herbs within hours and pull them out before nightfall. The color remained vibrant and the materials appeared fully dried and crumbly to the touch. The solar dryer excelled at drying herbs and flowers with an initial low moisture content. The basil, rosemary and spearmint all dried within hours and had similar color to the herbs dried in the electric dryer.
With large flowers like cockscomb celosia and large loads of flowers, we had better results leaving them in the solar dryer for two days. We dried large amounts of globe amaranth at one time, laying the flowers about three inches thick. This required more drying time since there was less air circulation and moisture got trapped between the flowers. Overall, we had excellent results drying flowers with much better color and consistency than air drying.
Another advantage to the solar dryer is the elbow room and variable headspace. The plastic cover could be raised and lowered and larger items could span more than one tray. In this way we were not limited by tray size and could pile on some awkward, large items like 3-foot stems of larkspur or branching basil. This dryer is designed to have a narrow passage between the product and the plastic cover. If the plastic is raised to accommodate larger items, it will also increase drying time because the tunnel will be wider and the air will not pass through as quickly.
We ran into challenges with this dryer when drying tomatoes because of their high initial moisture. With the exception of the hottest days, the tomatoes required more than one full day in the dryer. Unloading and reloading is labor intensive so it seems ideal to dry products in the solar dryer that take one day or less like the herbs and flowers.
A second problem with this dryer is that the area did not drain well after heavy rains when it was on a soil berm. Since we dug around the area to create a raised bed area for drying, the rain pooled near the dryer and took several days to dry after a hard rain.
In 2014, following the advice from the designers of the solar dryer, we built a platform to dry the product on. This reduced moisture and helped create a cleaner drying area. The platform was also much higher and ergonomic.
In both 2013 and 2014, the solar dryer excelled at drying herbs and flowers with an initial low moisture content. The basil, rosemary and spearmint all dried within hours and had similar color to the herbs dried in the electric dryer. Kale also dried well on this dryer on hot days.
The Chest Dryer
The second dryer utilizes electric heat and a fan, and it also based on plans from UC Davis. The electric dryer we built was based on a graduate student’s design from University of California at Davis (plan attached). It is a cabinet which can accommodate 18 trays in two stacked columns. The dryer has a small electric heater, fan, thermostat and vents. We hired a carpenter to build this model with supplies that cost about $600 but many farmers could build similar models on their own or by converting a small shed or outbuilding. The carpenter built both the dryers for $1,000.
The electric dryer did very well for us, with just a few hitches along the way. Everything we put in the electric dryer dried very nicely within 24-48 hours, and we could leave it running consecutively. The dryer is very clean and pest free. We calculated the energy cost of running the electric dryer to be about $1.40 per 24 hours of continuous use based on a cost of 9 cents per killowatt hour.
On the downside, we were limited to the tray size which meant a little more preparation for loading the dryer efficiently was needed. It did require checking, especially when the greenhouse it was sited in was already hot, to make sure it wasn’t getting too hot.
In 2013, we put the electric dyer in the corner of a high tunnel. On hot days, having the dryer in the tunnel must have saved energy by speeding drying times. However, there were also a few times when it was so hot in the greenhouse we had to make sure the dryer was not getting too hot. In the 2013 season we dried sweet potatoes, tomatoes, kale, basil, mint and hot peppers and flowers in the electric dryer.
During the 2014 season, we relocated the electric dryer to a cooler packing shed and replaced the fan. The dryer continued to run very well and dry products successfully. In 2014, we dried a large amount of tomatoes in the electric dryer. We dried several varieties including Big Beef, Mountain Magic and Iron Lady. The tomatoes lost virtually all their weight to evaporation. On August 15, nine pounds of sliced tomatoes on one try, went down to 5oz. Other trays had similar moisture loss (see table below). The before and after weights of four trays that day are given below. The ability of the dryer to adequately dry the tomatoes and other high moisture crops is clear.
August 15 Before and After Weights of Large Sliced Tomatoes
The Two Dryers
We decided to use 23 by 23 inch stainless steel mesh trays instead of plastic and to modify the specs so we could use the same trays interchangeably between the two dryers. The trays cost $15 each. This worked out well because most of the time we used one dryer or the other. For safety reasons, we chose to avoid using chrome, non-stick or plastic trays for drying. Nearly all commercial units use one of these materials so we decided to use stainless steel donut trays which were fairly affordable and very safe. We purchased the donut screens from Food Service Warehouse. (http://www.foodservicewarehouse.com/update-international/ds-23sq/p5486.aspx)
We tested the dryers over two seasons. We captured the weight of the products before and after drying and noted the consistency of the dried products. We experimented with different drying times and temperatures. The attached data sheet shows weights and drying duration for different batches of products. On the advice of an initial meeting with the Maryland Food Safety department we erred on the side of very dry products that would could break and crumble rather than bend. The data sheet shows that we reduced the weight of our dried products from 77% for kale to 93% for tomatoes. The 2013 products appear to be shelf stable after more than 12 months in storage.
The carpenter who built the dryer installed a thermometer which allowed us to adjust the temperature by turning the heating unit up or down and adjusting the vent. We were able to maintain a consistent temperature most of the time. Toward the end of drying cycles, temperature sometimes rose too high. Installing a thermostat that controls the heater or vent would clearly offer more temperature control.
We made one adjustment to how we prepared the tomatoes. The first few batches, we cut the tomatoes in circles and placed the inside of the tomatoes face down on the trays. This was a mistake. The tomatoes placed this way stuck to the tray and were difficult to peel off. The next time we cut the tomatoes in wedges and placed them skin down on the tray. This made all the difference. The tomatoes came off the tray easily after drying. We experimented with packaging products both with vacuum sealed bags and mason jars. As we worked we also refined our techniques with each product and sped up packaging.
The second part of our data collection was a taste testing on 6 products in the winter of 2013. We asked participants to rate our products on a scale of 1-5 for taste, appearance, texture and overall impressions. Our products received great reviews and helpful feedback which we applied in our second season.
Late in our project we purchased a digital relative humidity meter on the advice of our advisor James Thomson. This small device can be a huge help because you can easily calculate the available moisture in a sample based on the relative humidity (RH) reading. An RH of 40% means you have .4 available moisture. Most products need .6 or greater to grow any harmful bacteria. We look forward to using this more during future use of our dryers in order to gauge product safety without requiring lab testing for moisture content. We added the available water measurements to some of our samples on the data sheet. We found our samples were within the safe zone for available water.
We were very happy that we were able to dry so many varied products with success. There had been interest in this project from neighboring farms and others as a result of the public outreach. I shared the plans with farmers in other states and demonstrated the dryer in our community. I hope my project will help other farms start similar operations.
For more on outcomes see the accomplishments section below.
Licensing and Legal Hurdles:
So far our biggest hurdle has been getting our products approved for sale by the Maryland Department of Health. In a meeting with the state inspector, we learned the solar dryer cannot pass health inspection in our state because it is too exposed to the outdoors. We will therefore only use it for drying flowers, for which it is very well suited. The electric dryer can pass the health inspection but we must first construct a better building for it. The inspector found the shed in which it is now in too exposed to the outdoors. We plan build a building in 2015 for the dryer.
He thought he could approve the electric dryer for use in 2015 if we move it into a building with a fully enclosed space. If the building has running water, the inspector said we can prep vegetables in the building before putting them in the dryer. If not, we can get the kitchen certified and carry cut vegetables in closed containers from the kitchen to the dryer. We are also exploring obtaining a small shipping container or box from a box truck. The inspector advised us that both are good alternative to building a structure.
The health department inspector did not see a way to approve tomatoes or kale from our solar dryer because the design requires the product to be outside during the drying process. He did think it is possible to approve drying tea herbs that are intended to be boiled before they are consumed. This was discouraging, because we were able to dry greens like kale quite well in the solar dryer on hot days.
He also provided feedback on our packaging and raised concerns about the potential to grow botulism spores in our vacuum packed dried tomatoes. In 2013, we sealed bags of dried tomatoes and basil tightly by vacuuming out as much air as possible. The inspector advised that we seal the bags with some air to avoid an anaerobic environment hospitable to botulism. During 2015 year, we will do lab testing on all of the products before they can be approved for sale and will likely focus on the electric dryer for all products except teas and dried flowers.
We plan to revisit approval with the inspector with the added information of the easily measured available water from our new RH meter which shows our products are dried to safe levels.
Over all, we found the meetings with the health inspector very constructive and are now much more ready to market the dried products than in 2013. While we did not get to the point of bringing our product to market in 2014, we should be able to gain approval in 2015. Farmers in other states with different health department requirements may be able to gain approval faster.
We met our goals of building and testing the two dryers during the 2013 and 2014 seasons. We were able to build the two dryers at a very low cost and remain within our planned budget. Our electric cabinet dryer is comparable to units that sell from $6,000 of $20,000 and was constructed for less than $600 in materials. The solar dryer cost even less to construct and is free to run.
We tested the two dryers on various crops including tomatoes, kale, herbs, sweet potatoes, and flowers. During 2014, we made modifications to both dryers to and began to develop a protocol for successful use of the two dryers. The main modification to the solar dryer was putting it up on 3ft high table to reduce moisture from the ground. We replaced a plastic fan in the electric dryer with a metal fan. We were able to create attractive and tasty value added products from the excess produce on our farm including dried tomatoes, kale and herbs.
During the winter of 2014, we held a successful tasting event where participants tried six of our products. We included our chef consultant Tom Meuller in the tasting. We were quite pleased with the results of our tasting. The tomatoes, kale and basil all received great reviews and we hope to have these products market ready in 2015. We find our dried tomatoes are excellent to use after we soak them in water and saute them in olive oil.
The dried flowers have enormous potential for us. Unlike with fresh flowers, there is no issue with needing to sell a large amount of blooming flowers at one time. Nor are there concerns with vase life. The dried flowers are a product we can potentially wholesale to florists or floral distributors in large numbers without the time pressure associated with fresh flowers. Some of the dried flowers like the cornflower have potential for sale as decorative food items such as confetti for catering trays.
Education & Outreach Activities and Participation Summary
We completed the outreach phase of this grant in early 2014. I spoke at two regional conferences and published an article in a national magazine. In all of these venues, I shared our experience, our dryer plans and information about the SARE program and grants.
1) I spoke on a SARE panel at the Future Harvest/Casa conference in College Park Maryland. This is a gathering of organic and sustainable farmers, advocates and educators from the whole Chesapeake Bay region. I created a Powerpoint presentation and shared my experience using the two driers. There were 30 participants in the panel.
2) I presented a similar presentation at the Maryland Organic Food and Farmers meeting in Annapolis, MD in February 2014. There were about 30 farmers in attendance and there was time for discussion and questions. I will offer follow up information at the 2015 MOFFA meeting.
3) I published an article in Acres USA in March of 2014 about the grant and my experience using the dehydrators. As a result of the article, I responded to several email inquiries from farmers in the US who were interested in more information and plans.
4) We shared our dryers with local farmers and friends who were interested in learning and drying some of their own excess crop like hot peppers.
The project demonstrated that for a small capital investment farmers can build commercial scale food dehydrators that work well on various products. We were also able to successfully spread the word about our work to many other farmers both in the region and nationwide.
While the project did not go as far as we hoped in the first two years, our struggles with licensing were instructive. We did not anticipate having to build a separate structure for the electric dryer but should be able to do this for an additional $2,000. Farmers without adequate outbuildings should consider partnering with an existing commercial kitchen or building a packing shed that can accommodate the electric dryer and packing area.
Farm scale dehydrators could be a huge asset for many small scale farms. There is tremendous potential to create a wide range of value added products including teas, flowers, dried snacks and more.
Further research would be helpful to define best practices for drying and packing dried produce on a small scale including use of the affordable RH meter to test for available water. The use of available water as a measurement should be promoted among farmers who are interested in marketing dried foods. There is some information availalble including this helpful piece from Clemson University in North Carolina (http://www.clemson.edu/extension/food_nutrition/canning/tips/39available_moisture.html).
If best practices were defined on a national level, it would help to facilitate more small scale operations. It might be also be helpful for farmers to work in cooperatives or with chefs or food hubs for drying and packing as an alternative to on farm processing.