The way mint oil is extracted from the plant after harvest may soon become much less costly and more efficient, if tests now being conducted at the University of Oregon prove out.
Mint oil has been traditionally extracted with the use of steam.
The cost of producing that steam has become progressively more expensive, until it has reached a point of diminishing returns, according to the Washington Mint Growers Association.
The energy source used in the steam distillation process has been petroleum based, either diesel or natural gas, which was used to heat the boilers that produced the steam.
That process has remained essentially the same for nearly 100 years, but in the last several years, the cost of petroleum-based energy has risen to the point that it is the single most expensive input in the production of mint oil.
Since 2004, tests have been underway to demonstrate the feasibility and effectiveness of solvent-free microwave extraction methods.
According to information provided by the association, it has been confirmed in the laboratory using 100-gram samples of mint hay that from 30 to 60 percent of the energy used in the steam distillation process can be saved with the microwave process.
There are also many other benefits, such as environmental stewardship, reduction of labor costs, management flexibility, and significant water savings.
The microwave process eliminates the need to introduce water into the distillation process, because it uses a portion of the water already in the harvested crop to create the necessary steam.
The hay residue produced by the microwave process is dry, rather than moist, as in the traditional method, and is thus much lighter and could be easily baled and offered to the marketplace similar to peat moss or other similar products.
With the microwave process, there is no boiler, no boiler maintenance, and no petroleum source needed.
The microwave process requires no warm-up time, and eliminates the greenhouse gases that would be generated by a petroleum-fired boiler.
In laboratory testing, mint-oil condensate was produced and collected within 10 seconds after microwave heating was initiated, according to the information provided by the association.
The laboratory 100-gram testing was followed by testing of sample sizes from 100 to 1000 times the size of the initial tests.
That was so promising that the decision was made to develop a field test unit for use this summer.  
Existing equipment will be used to create the field test unit that will move mint hay from a standard tub or alternate transport tub onto a conveyor belt that will pass the hay through a microwave applicator.
Experimenters believe that a microwave processor could be made mobile, similar to a combine used for seed crops, that could collect mint oil directly from the field.
Testing will be carried out this summer, and the experiments conducted will be the first direct comparison of chopped mint hay by steam distillation and chopped mint hay by microwave extraction.
Support for the experiments will be provided by the Washington Mint Growers, Oregon Mint Growers, and the Mint Industry Research Council.