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       Chris Callahan
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       Rutland, VT 05701
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UVM Extension AgEngineering Blog

Processing Mature Green Tomatoes

Posted: July 2nd, 2014 by Chris Callahan

Solar Hot Water Heating in Vermont Greenhouses

Posted: May 14th, 2014 by Chris Callahan

Biomass Heating in Vermont Greenhouses

Posted: May 13th, 2014 by Chris Callahan

Farm to Plate Energy Success Stories

Posted: March 11th, 2014 by Chris Callahan

Vermont’s Comprehensive Energy Plan calls for obtaining 90% of the state’s energy from renewable sources by 2050 and reduce greenhouse gas emissions 50% from a 1990 baseline. What role can Vermont’s food system play in advancing this goal?

The Energy Cross-cutting Team of the Farm to Plate Network has released seven Energy Success Stories that showcase farms, businesses, vendors, installers, and technical assistance providers that have made a difference with energy efficiency savings and renewable energy production.

The stories were prepared by JJ Vandette and staff at Efficiency Vermont, Chris Callahan from UVM Extension, Alex DePillis from the Agency of Agriculture, and Sarah Galbraith and Scott Sawyer at VSJF. Funding for the project was provided by the Northeast Dairy Sustainability Collaborative (Ben & Jerry’s, Cabot Creamery Cooperative, Organic Valley, Stonyfield, Vermont Agency of Agriculture, and the Sustainable Food Lab).

The seven Energy Success Stories are the first in a series of resources that will highlight farms and businesses throughout Vermont’s food system that have made significant progress in saving energy and producing renewable energy.

The first 7 Energy Success Stories can be found on the Atlas at these links:

They can also be downloaded as PDFs here:


DIY Auto-fill Humidifier

Posted: March 4th, 2014 by Chris Callahan

I recently built a humidifier I think others might find useful.  This could be useful for cheese aging, meat curing, and storage of winter crops all of which require maintaining specific temperature and humidity. The details are available on the Tool Wiki at FarmHack.  Take a look, and let me know if you find ways to improve it or if you have any questions.  As part of this project I also developed this handy spreadsheet that calculates relative humidity based on dry-bulb and wet-bulb temperature and/or calculates wet-bulb temperature based on dry-bulb temperature and relative humidity.  The spreadsheet also helps you tailor the humidifier design to your needs by estimating humidification capacity in gallons of water evaporated per 24 hours.

The idea was to turn a 5 gallon bucket into a high capacity (4 gal/day), automatic fill humidifier. The bucket serves as a reservoir for the water and also as a mounting platform for the parts required to operate the humidifier. Water heated to a know temperature will transfer a predictable amount of water vapor to an air stream of a known temperature and humidity (wet bulb temperature). We use this property to develop a highly controlled humidifier using a temperature control to sense water temperature and control the heater, tank deicer for heat, and a CPU fan for air flow. We also add a toilet fill valve to the assembly to allow for automatic fill of the humidifier.


Oilseed Economics Update 2014

Posted: March 4th, 2014 by Chris Callahan

Yesterday we held our annual Oilseed Producer’s Meeting.  At this meeting, I presented an economic overview of oilseeds in Vermont.  Ina nutshell, Vermont has an installed on-farm biodiesel capacity of 600,000 gal/yr (5 sites) with a normalized initial cost of $1/gal of capacity (better than national average). Fuel can be produced for an average cost of $2.13/gal, and meal can be produced at an average cost of $340/ton.  The greenhouse gas emissions associated with this model are 60-100% better than US avg oilseed production (net sink) while the average energy return on energy invested (EROEI) is 4 to 1 (i.e. 4 gallons produced for every gallon used in production.  The model is on-farm production for on-farm use; i.e. cost avoidance.

This study made use of the Vermont Oilseed Cost and Profit Calculator, a tool we have developed over the years to collect all the enterprise costs associated with an on-farm oilseed operation that may turn the crop into meal, oil, and/or biodiesel.  It helps growers and others interested in the topic arrive at specific product costs and compare those costs to market prices.  We also have summarized three different likely oilseed enterprise scenarios in e report titled Vermont On-Farm Oilseed Enterprises: Production Capacity and Breakeven Economics. This work has had strong support from the Vermont Bioenergy Initiative of the Vermont Sustainable Jobs Fund and has been accomplished in close cooperation with the UVM Extension Northwest Crops and Soils Program.

Small Scale Oilseed Press Evaulations

Posted: March 2nd, 2014 by Chris Callahan

We recently completed a series of small scale oilseed press evaluations related to on-farm oilseed processing.  The video below summarizes the different presses and a full report is available for download.

UVM Hops Harvester, Yellow Dog Hopyard and Rock Art Brewery on Across the Fence

Posted: March 2nd, 2014 by Chris Callahan

Across the Fence, the longest running daily farm and home television program in the country, joined us when we were harvesting last summer with the UVM Mobile Hops Harvester. In this segment, hear from Nick Aleria of Yellow Dog Hopyard in Cabot. VT and Matt Nadeau of Rock Art Brewery in Morrisville, VT about how local hops are important to their businesses and how the machine has helped this to be feasible. Across the Fence is a 15 minute program produced by University of Vermont Extension. The program airs weekdays at 12:10 pm on WCAX TV, Channel 3.

Greenhouse & Tunnel Tour Video Series

Posted: January 27th, 2014 by Chris Callahan

Hop Harvesting Roundup

Posted: January 7th, 2014 by Chris Callahan

I recently presented a summary of mechanical hop harvesters at the 2013 NEHA Hops Conference in Morrisville, NY.  As I prepared that material I was struck by how far we’ve come since 2010. In just three years since our small team embarked upon the development of the UVM Mobile Hops Harvester, several independently designed mechanical harvesters have become available and several builds of the UVM type harvester have also been developed by others. These are summarized in the presentation file linked above including videos of some of them.

Does Mechanical Harvesting Pay?

I also thought it may be helpful to show the impact of mechanical harvesting on a small hop farm. The reality is that hand picking hops is only realistic early in the development of a hop farm and only at very small scales of production. It depends on the interest of the pickers and the community atmosphere that many growers develop around their young enterprises.  However, it is unlikely that the hand picking can support larger volume production at current labor rates and the rate of harvest will also be slower than necessary for preserving maximum hop quality.

So how expensive is a mechanical harvester? And can it actually pay for itself? Let’s do the numbers.

Assume a machine cost of $20,000, assembled, installed and ready to go (actual costs for the available machines are included in the presentation file above).  Let’s say that machine is capable of harvesting 60 bines per hour (a light load for most) and that each bine is yielding 1 dry pound of hops.  Let’s also assume 1000 bines per acre, and a one acre yard. We’ll look at high volume scenarios later.  The benefit of mechanical harvesting is labor savings, so we need to assume the base case is paid hand picking at a wage of $7.25 per hour and a rate of 1 dry pound per hour (about one bine). Let’s also note that the machine might require 4 people vs. the one person we’re comparing it to, so it has a higher “per hour” labor rate. We’ll also assume that the machine has a life of 20 years, over which it’s initial cost is spread (as though it is being depreciated like other assets).

We have to make one simplification to the calculation before proceeding. We need to assume a common gross profit prior to harvest.  In other words, the cost of the yard structure, the rhizomes, water, nutrients, any pest and disease management, etc. is all the same between the two cases and allows for a gross profit of, say, $10 per dry pound. With all that laid out, we can summarize the case as shown in the following table.

Yard size 1 acre
Density 1000 bines per acre
Plant yield 1 dry pound per bine
Gross profit prior to harvest  $10.00 per dry pound
Machine cost  $20,000 initial
Machine life 20 years
Machine rate 60 bines per hour
Machine labor 4 persons
Labor cost  $7.25 per hour
Hand picking rate 1 bines per hour
Machine harvest cost  $1.48 per dry pound
Hand picking cost  $7.25 per dry pound
Mechanical advantage  $5.77 per dry pound
 $5,767 annually
Simple payback period
Ammortized 0.2 years
Non-ammortized 3.5 years

Admittedly, we can argue over the assumptions presented here.  A machine could cost more to build or buy than I have assumed.  Someone may be able to hand pick much quicker than I have presented.  The machine rate could (and probably will be) higher than assumed above. The gross profit of $10 per dry pound assumed may be more or less.  But I think it is safe to say that mechanical harvesting can pay for itself and, perhaps as important, allows a certain scale and quality of production that isn’t supported by hand picking.

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