To download the PDF version of this plan click here!
Farms that need to cool smaller volumes of produce can also benefit from forced air cooling. Whether cooling stacked pallets, pallet bins or individual cartons, the same principals apply. A smaller pallet cooler was noted on the previous page, but this concept can be scaled down even further to fit your needs. Here is a prototype, that could fit on a countertop with-in a walk-in cooler.
Constructed of 2×4’s on top of a horizontal base made from 1/2” plywood cut 24” deep and 44” wide. Angled reinforcements were needed to stiffen the assembly.
A downloadable/printable pdf of this article is available here.
The preservation of quality in fresh market and storage crops on small and medium-sized farms in the Northeast depends on the rapid reduction of pulp temperature and maintenance of relatively low temperatures to slow metabolic respiration.
There is strong foundational work showing that rapidly reducing the temperature at the start of the cold chain increases product quality when delivered to the consumer. Postharvest handling is critical for fresh produce farmers and the markets they sell to. Effort and expense invested in growing fruits and vegetables can be wasted without good handling practices at and following harvest (Gross 2014). Consumers expect the best from fresh produce. Quality and freshness are ranked with high importance among consumers. Farmers market respondents respectively rank quality (63% ) and freshness (59%), as highly important factors in their buying decisions. Nearly 87% of the respondents indicated that availability and quality of fresh produce affected their decision about where to purchase (Gorindasamy 2002).
Precooling involves flowing a controlled, chilled fluid (air or water) over the product to improve heat transfer for removal of field heat to depress respiration and initiate the cold chain.
One of the most important postharvest factors influencing quality is temperature. Temperature directly impacts the rate of metabolic respiration and associated decay. Produce which is not cooled quickly degrades in quality (Sargeant 1991). Table grapes, for example, deteriorate more in 1 hour at 90 °F then in one day at 39 °F or one week at 32 °F (Thomson et al 2008). Lower quality leads to a decrease in sales, inefficient use of storage space, and wasted labor due to the time taken to grow, clean, and store product that doesn’t sell. Coolers are a good addition to most farms but fall short of meeting optimal precooling needs. When produce is packed in boxes, stacked on a pallet and directly placed into a cooler, cooling time will be a minimum of 24 hours and may take many days. (Thompson et al 2008).
One method to reduce cooling time is through forced air cooling (FAC). In FAC systems, refrigeration cools a space and blowers are set in position to actively draw the cold air through the produce. The cooling time drops from 24 hours to 10 hours or less when using a static cold room due to the increased air flow (increased convective heat transfer) (Thompson et al 2008, Boyette 1989).
Attempts have been made at smaller scale pre-coolers to reduce field heat at harvest in absence of coolers (Thompson and Spinoglio 1996). Retrofitting a cargo container with insulation and cooling with a large capacity air conditioner was also explored (Boyette & Rohrbach 1990). This forced-air cold room offered space for many pallets of produce but it still took many hours to reduce the temperature internally, especially for the boxes on pallets in the center of the container. The key is integrating both cooling and air flow effectively (see Figures 1 & 2).
A mobile forced air cold box mounted on a trailer was constructed and demonstrated in Florida (Talbot and Fletcher 1993) aimed at farms growing produce on 5-50 acres. This unit could be self-built. Experiments showed that grapes could be cooled by 15 °F per hour. For denser produce like melons and tomatoes, the cooling times were longer. The construction cost at that time was close to $5,000.
We have built prototype FAC’s for a single, fully or partially loaded pallet (figure 2) and also a 1-3 carton (either bulb crate or 1 1/9th bushel box) “counter-top” model. The construction details of these units are provided on the following pages of the PDF linked above.
Key Points of Precooling
Starts the cold chain by rapidly reducing respiration.
Reduced respiration leads to higher quality over a longer storage and distribution time.
Cooling is improved with the combination of active cooling and forced air flow with a blower.
1-3 CFM of airflow at 0.5 IWC static pressure per pound of product is the rule of thumb for sizing.
Ventilated containers (e.g. holes or slats) are necessary to ensure airflow is actually through the product.
Close up any large openings to prevent short-circuiting air flow.
Sound like a good idea to you? Build plans are available for both of these prototypes!
It is easy to ignore the thing beneath our feet, but floors are an important part of produce wash and pack areas that deserve special attention. They can impact efficiency, ergonomics, employee health, worker fatigue, personnel safety, and produce safety. There are also a number of design features involved with these seemingly simple structures that should be considered1,2.
No two wash-pack areas are the same. Every farm has different needs driven by different crops, scales of production, layout, existing infrastructure, and management approaches.
Smaller market farms may have a very simple, open packshed design consisting of “four sticks and a lid” used primarily during the summer months. The floor of these structures could be anything: a dirt floor, grass, or gravel surface. If you choose to have a dirt floor, consider laying down weed mat or landscape fabric to create a tidy work environment. It is helpful to consider drainage, specifically providing intentional drains from wash tanks and sinks that direct outflow away from the work area, production areas and bodies of water. The intent is to keep the surface underfoot relatively dry and free of standing water, prevent cross-contamination between drainage water and production areas and to prevent nutrient loading in bodies of water.
Larger farms and those engaged in season extension and winter markets may find benefit from an improved floor, permanent roof and walls. When scaling up, consider the benefits of an enclosed packshed which can provide:
Protection from the elements as you work further into the shoulder seasons. Cooler working environment in the summer for you, your crew, the produce, and your equipment or warmer (if heated) in the fall, winter, and spring.
Cleaner environment for handling produce and storing containers. An enclosed space is more “cleanable” as it has doors and windows to keep dust, bugs, birds and other wildlife away from you and your produce.
This presentation was given by Chris Callahan from at the Great Lakes Expo in Grand Rapids Michigan in December 2017. He discusses the differences between fruit and vegetable storage needs, finish surfaces for wash/pack areas or coolers as well as temperature and humidity controls.
A frequently asked question we get is about vapor barrier usage in coolers. See Chris’ answer below addressing that question. This video shot is pulled from the above presentation and was shared on our Instagram page.
This conference is filled with a variety of vendors at the trade show, presentations covering specific details of individual crops and varieties, and even talks on designing your farm with an eye on food safety. Another interesting activity that went on was the farmer to farmer sessions that are not presentations but a lead conversation to discuss what works and what doesn’t on your farm. A lot of tips, tricks, and common complaints are all brought up and shared during this literally circled up conversation.
If you’ve never been here are a few photos from the event, which was very snowy in mid-December.
Here is a short highlight video from the conference!
In December, UVM Ag Engineering ventured out to Grand Rapids, MI to attend the Great Lakes Expo.
This exposition was HUGE and full of a variety of seed companies, equipment suppliers, and machinery on display. There was a lot of technology targeted towards fruit growing which is big in that region which was neat to see.
Native Son farm is a small diversified vegetable farm in Tupelo Mississippi, who had been washing vegetables by hand and started looking at automated wash lines. With zero experience on automated washing, he began first researching the common barrel washer, reading reviews, and watching videos online. Will Reed reached out to Deerfield Supply out Kentucky who distributed AZS equipment. Upon meeting Harvey from AZS, he learned about the rinse conveyor, which is less aggressive on the crops than a barrel washer. It is also designed with cleaning in mind which has a high level of food safety appeal.