For an
oilseed press to operate properly, the incoming seed must be clean and of the proper moisture content. Seed cleaning and storage information is provided in a separate fact sheet, “Oilseed Cleaning and Storage”.
Generally 10% is used as a rule of thumb for the moisture content at which to store grain and seeds. While the seed will store well at this moisture content, it most likely will not press well. Seed that is too moist will produce meal that is gummy and will not produce oil as it passes through the press. The moisture in the seed ties up the oil and does not allow the oil and meal to separate as it should.
All grains have moisture contents at which they press best. A general rule to start from is that the ideal moisture for pressing is in the 7-8% range. Experience shows canola presses best in the 6-8% moisture content range, with other oilseeds requiring similar moisture contents. If the moisture content of the seed being pressed drops too low the temperature of the press head increases when pressing and will make it difficult to stay under the 120F (50C) temperature limit for cold pressed oil if that is important to the operation. Lower moisture content seeds result in higher press temperatures and a lower yield of oil.
Moisture content is often the culprit if pressing is difficult. On one occasion, bags of canola at 7% moisture content to be pressed were placed on the floor of the pressing area. When pressing time came a week later, the seed would not press. After numerous failed attempts at getting the press started with this seed, the moisture content was tested again and had dropped to 4%. Unknowingly the seed had been stored directly under a heating vent and had dried considerably by heated air blowing across the bags.
For information on moisture con-tents for pressing, consult someone familiar with press operation. Often an email or phone call to the press manufacturer will help in getting started on a new type of seed. When an opportunity to press Brazil nuts was presented, an email to the manufacturer delivered the news that the press barrel needed to be heated to about 93C (200 F) for pressing to work correctly with this high oil con-tent nut. Without this information a great deal of time was used unproductively as various lower temperatures, speeds and tip sizes were unsuccessfully tried.
