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what are good methods of oil extraction from plant materials?

 
Thekla McDaniels
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I know there are industrial presses made in India, or ? that cost in the 20,000 (US) dollars, and there are the hand crank ones that use the warmth of a candle or oil flame to warm the oil being pressed to make it flow.

Neither of these seems just right for me. Surely people were pressing oil before the industrial revolution! Does anyone have any ideas how it was done, or how to go about it?
 
John Elliott
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Thekla McDaniels wrote:I know there are industrial presses made in India, or ? that cost in the 20,000 (US) dollars, and there are the hand crank ones that use the warmth of a candle or oil flame to warm the oil being pressed to make it flow.

Neither of these seems just right for me. Surely people were pressing oil before the industrial revolution! Does anyone have any ideas how it was done, or how to go about it?


OK, as one of the resident chemists, I'll take a stab at this along with your other question:

What is anyone growing on perennials to press for oil? I can think of olives (but who would want to burn such precious stuff), hazel and other nuts, rosehip seeds make a nice cosmetic oil, but again, would fuel oil be a good use for that?


The development of this particular bit of chemical technology is lost in antiquity and probably predates soap making -- for to make soap from ashes and fat, you have to have some nice clean fatty acid molecules. I would guess that the first oils to be kept for storage were those that congealed overnight after a big repast on some piece of fatty game. And the technology really got a boost with the invention of the clay pot. All you had to do is boil up some fat containing biomass and let it sit out in the cool of the night. In the morning, you carefully lift off the fat that has risen to the top and congealed.

Now boiling may be fine for a low-tech operation, but heating water uses a lot of fuel and fats have next to no solubility in water, so you have to make sure that cell vesicles rupture and release their oil in the cooking process. Some biological structures take a long time to break down and release their trapped oils, so the next step is to use a solvent more active than water that can extract the oil molecule. These are known as "defatting solvents", which by the way you don't want to be getting on your skin, because they will also remove skin oils that you would really rather retain. Peanut flour is made by defatting peanut butter, and many solvents are possible: hexane, acetone, carbon tetrachloride, whatever is on sale in the paint aisle of the hardware store. This is not known by the general public, but if they were to complain, the food technology engineer's answer would be "what are you worried about, all the solvent is extracted in the next step and recycled".

His protestations aside, most people will pay a premium for extra virgin olive oil, molecules that have been gently coaxed from the olive without the use of solvents. If you want to find home setups for pressing oil, it helps to search for it in Italian, like this video I found on YouTube:



Since I live in Georgia, the ubiquitous oilseed is the peanut, although I have heard of small experimental olive orchards here. I've grown peanuts, but never enough to be making large quantities of peanut butter, peanut flour, and peanut oil. I've also grown sunflowers, and that would be my second choice for an oilseed adapted to my climate. I think the answer to what oilseed is best is whatever does well in your area. Most seeds contain oil to give the plant seedling a nutritional boost, so if there is some prolific "weed" in your area, collect up the seeds, grind them and boil them, and see how much oil floats to the top.
 
C. Letellier
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Location: Greybull WY north central WY zone 4 bordering on 3
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For olives and some other oil crops the original method was stone wheels. Here is a youtube video of one of them. Skip in to 1:50 for the start of the actual pressing operation as before that is picking and other.



If you do a google search for "stone wheel olive oil" and go down to the images result you can see there are hundreds of designs for the stone wheels. They did the crushing and in some cases were set up gather through special channels and small holes the very first of the oil. Notice how they press it afterwards in the video with a screw press and basket weave filters. This was often done a couple of times repeated of crushing then pressing. The first pressing was considered to be better oil as it was what came easily out. The pulp goes back under the wheel and the process is repeated. This along with heat was a whole lot of the process before the industrial revolution and the evolution of solvent wash techniques to get more oil out.

I remember reading about a water powered centrifuge used in I think it was Greece? that you might go looking for. It use for olive oil was one of the first uses of a centrifuge as an industrial process and dated back a long ways. It is how it is done on an industrial scale now.

The other common modern method is the filter press. These can be fairly simple or really complex. Here is a link to simple version for olives but it would likely do almost any oil. Notice that most of it could probably be replaced to do this small scale on the cheap. The press frame itself you can buy though places like harbor freight fairly cheaply. Odds are if you are rural you have a neighbor with such a press in his shop already. The grinder you could likely replace with a meat grinder running a fine cut plate or maybe a blender or food processor. The mixer for oil droplet process you could likely substitute a beater mixer or bread dough hook on a small scale and at the bucket scale rigging something like their mixer is readily doable. So basically the stuff to actually go in the press is all you would need to start likely if you use your head for substitutes.

Simple olive oil press

From there the filter press can change for larger scales. I have never been around them for food or oil but about 15 years ago I did attend a class on them for processing radiator shop sludge from the sump. But the same type of equipment would easily work for food grade stuff as it is all available in food safe rated materials. The commercial set up for it sold for something like $10k or $12k but the guy had built his own for about $3000. They started with a 30 gallon plastic barrel of sludge shoveled out of the sump. Normally they would have sucked straight from the sump but for the class they brought it into where we were seated. The pump was an air operated double chamber sludge pump.(many of these have food safe ratings on them) From it went to a stack of special square ceramic plates with filter membranes in them. There are 2 end plates and count of the plates in between can be varied. Each plate was about 1 foot square and 2 inches thick. The cavity in the middle was roughly 8 inches square and the plates sealed together with o-rings. Apparently the plates were about about each $250 back then and the membranes were something like $25 each. His home built frame was built so he could add more plates later. They use their shop porta-power to push the o-rings together.(hydraulic jack would work fine here). The membranes filtered to 1/2 micron. The sludge was about the consistency of runny concrete for the thicker part down to almost water at the surface. As the pump ran the clear water came out the outflow tube. They did the whole 30 gallon barrel of sludge in 2 emptyings of the press filters. The first batch that ran sludge till the pump stalled felt dry to your hand. The second batch because he ran out of sludge and couldn't pack it as tight felt mildly damp. It was amazing how clear the water coming out was. I had been familiar with household filters at 5 microns that the water was still cloudy. That wasn't the case here. The water was totally clear. It had gone from mud to clear water and basically dry packed dirt. The ceramic plate boxes said they were food safe right on them and the filter membranes. The pumps I know from the catalogs are available in food safe materials. So a couple of food safe hoses and containers is all that is left. The neat thing is that while the guy had only done 3 center plates if he later decided he wanted 10 or 20 plates he simply needed to add plates to his frame. Some of the industrial presses can have hundreds of plates in a single frame.

Now the final one I am familiar with from researching biodiesel production is twin screw extruders presses. They get a lesser percentage oil out but the neat thing is they are continuous operation not batch. The video I watched there they had shopped US made ones but couldn't find one they thought they could afford so they had found a cheap chinese import for something like 1/10 the price. They went on to list all the problems they had to solve to get it working. Cheap has its price. They ran corn through this extruder all day every day and fed the output of the crushed grain to the livestock daily since it apparently spoils through oxidation fairly quickly. But because of the heat and friction of going through the press it was cooked somewhat and that apparently raised its food value to livestock so they actually figured they were losing very little in spite of removing part of the oil. Depending on what you wanted to do this might be worth researching.
 
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