Biodiesel Glossary

  1. Cold-press
  2. Hot-press
  3. Full-press
  4. Pre-press
  5. Degumming
  6. Phosphatides
  7. Neutralizing
  8. Free Fatty Acid (FFA)
  9. Soapstock

Cold-press: the seed is not heated at all or its initial temperature is only slightly increased by approximately 20 °C before entering the presses. Depending on processing conditions the residual oil in the cake will be between 10 to 14%, which is 2 to 4% higher than running a hot, full-press system. Because of its inefficiency, a cold-press system is typically used for low capacities of 100 MTD or less of seed throughput.

Because of the gentle seed treatment the oil obtained in a cold-press system is of the highest quality (e.g. cold-pressed virgin olive oil) because it contains the lowest amount of free-fatty acids and phosphatides. The oil usually commands a premium when used for human food consumption. Depending on the seed quality and processing conditions the obtained oil may not need further processing such as degumming and neutralizing before the transesterification process (biodiesel process).

[Biodiesel Glossary]

Hot-press: is the process that is widely used with a full-press or prepress system because of its higher oil yield. The incoming seed is heated in a conditioner and/or cooker to temperatures between 80 and 105 °C prior to entering the expeller press. Compared to the "cold-press" mode, the high temperature allows for a lower residual oil in the cake by 2 to 4%.

A hot press system reduces the required horsepower in the presses and also minimizes the wear and tear. The disadvantage in comparison to the cold-press system is the lower oil quality, which will require further refining to make it suitable for the biodiesel process.

[Biodiesel Glossary]

Full-press: the seed is squeezed as much as possible in the expeller press, leaving a minimum of residual oil in the cake (meal). Typical results are between 8 and 10% of oil in the cake. Within a certain range one can adjust the equipment and operating conditions to lower the residual oil in the cake. However, under such circumstances, due to the higher friction and heat built-up of the cake in the expeller press the risk is high for degradation of the protein, resulting in a lower commercial value when used for animal feed. In a full-press operation the obtained cake is not further processed in a solvent extraction.

[Biodiesel Glossary]

Pre-press: the seed is more "gently" squeezed to obtain a residual oil of about 16 to 22% in the cake. The cake is then further processed in a solvent extraction process where it becomes "meal" with approximately 1% residual oil. It is generally accepted that, depending on market conditions for the oil and the meal, a pre-press /solvent extraction system becomes economically feasible with capacities above 750 MT to 1,000 MT/day.

[Biodiesel Glossary]

Degumming: generic expression for removal of phosphatides.

Phosphatides: also called a "gum": chemical combination of an alcohol with phosphoric acid and a nitrogen compound.

Neutralizing: removal of free fatty acids, trace metals.

Free Fatty Acid (FFA): a fatty acid that is split from a triglyceride by hydrolysis.

Soapstock: the by-product from the neutralizing step containing soap, gums, water, oil and other impurities.

[Biodiesel Glossary]