Throughout the years there has been a fascination with pressing alfalfa. At this point the activities in the United States have almost all ceased operation; however, we know many plants are in operation in Europe. Recently we learned of seventeen alfalfa pressing plants in France alone.
Generally incoming shredded alfalfa will have a moisture content of 80% to 85%. This is reduced to 65% to 72% in the press cake. This corresponds with producing approximately 55 pounds of press liquor (with 7% dissolved solids) for every 100 pounds of alfalfa introduced into the press.
Our applications file indicates that fresh cut alfalfa will have a bulk density of 10 to 12 pounds per cubic foot (p/cf). This increases to about 24 p/cf when the alfalfa is run through a shredder. At the same time, a project in Minnesota that is in the study stages calls for macerated alfalfa at 40 p/cf. In any case, it is important to harvest the green, young alfalfa during the morning hours while it has its highest moisture content.
The principal product made from pressing alfalfa is a chicken feed additive. The additive is very high in protein content, and, like marigold extract, it results in yellow egg yolks in layers and yellow skins in broilers.
To make this additive, alfalfa press liquor is run across screens to take out fiber and suspended solids. Then the greenish juice is heated to 190Âº to 195Âº F which coagulates the green protein. This forms a brown mass (that looks like cottage cheese or curd) that is centrifuged to pull out the coagulated material. These solids are run through a rotary dryer to produce the high value feed additive.
The liquor from the centrifuge is concentrated and sold as molasses. A waste heat evaporator is used in the concentration process to take advantage of waste energy from the drum dryer. Early installations had Vincent WHE's, dryers and presses.
In 1993 the U.K. based sugar beet company, Western Sugar of Denver, Colorado, did some testing on alfalfa. They bought a Vincent VP-12 press for the tests with the idea of using their existing sugar evaporators in the off season. They knew this was being done in Denmark. The tests were successful, but the project was never funded.
At Western Sugar it was found that our press achieved close (90%?) to the "brochure" throughput rating when the alfalfa was macerated. On the other hand, a capacity de-rating of 40% was evident when the alfalfa was only forage chopped (1" to 1-1/2" pieces).
When large volumes of forage chopped material are fed to Vincent presses, the machines require a great deal of horsepower. For this reason very heavy duty drive components and screens are used on alfalfa machines. Starting with double the normal horsepower, we go to a large diameter shaft and thicker screw flighting.
There is a project at Phytolife Science. Their original work used a Russian technology that involves growing alfalfa on soils that have been contaminated with radioactivity. As the alfalfa grows, it absorbs the radioactive particles. The alfalfa is pressed in the process of concentrating the radioactive waste. They use electromembrane separation of the juice to take out the fraction with the contaminants. Fortunately from the pressing standpoint, they macerate the alfalfa to destroy the cell wall.
When DOE funding for the radioactive project was delayed, the same group shifted to working with a cosmetics firm. Their program called for pressing alfalfa to produce a component for cosmetics. A pilot test plant was built with a Vincent press.
In 1966 Vincent sold a VP-12 press to Standard Process of Palmyra, Wisconsin. The company produces natural vitamins and herbs. They successfully press alfalfa as part of a process of producing health foods for human consumption.
Testing with the new Vincent Twin Screw Press indicates that this machine design may be superior to other presses for use on alfalfa.