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The paper describes a mobile extractor for wet fractionation of alfalfa. The extractor was equipped with vertical hammermills and a screw press. During a first experiment, two chop lengths (8.9 and 17.7 mm), three levels of feed rate (ranging from 81 to 451 kg/h) and two types of hammer (flat edge, V-edge) were evaluated in terms of extraction ratio of total mass, dry matter and protein. The degree of cell rupture (DCR) was also evaluated by measuring the release of chlorophyll A after the hammermill process. Results showed that the extractor removed on average 43% of the total wet mass and 38% of the protein from fresh alfalfa initially at 76% moisture. The extraction of protein was increased with a shorter chop length and with the flat edge hammers. Environmental factors such as a colder ambient temperature and a higher initial moisture of fresh alfalfa also increased the extraction ratio for protein. A coefficient of determination (R2) of 33% was obtained between the protein extraction ratio and the DCR. During a second experiment, the wet milled fiber was processed twice through the screw press. The second press treatment increased total mass extraction by 23% (from 44.1 to 54.3%) and protein extraction by 16% (from 36.7 to 42.4%). The extractor could be easily moved from farm to farm, and to various regions for the extraction of specialty ingredients in alfalfa.