I spend several hours daily now picking walnuts and laying them out in a designated room to dry. Some days “just” one bucket, other days more. And since we did not eat all walnuts from last year yet, I have been thinking about how to process them in a useful way. And I have decided to try to make walnut oil. I have wasted two kg of low-grade walnuts and one kilo of moderately good ones trying to devise a process that works and I did come up with one in the end.
The first try cost me three hours of work, 700 ml of acetone, and resulted in barely 50 ml of oil from 1 kg of shelled walnuts. Not good.
The second try cost me five hours of work, 1400 ml of acetone, and resulted in roughly 150 ml of oil from 1 kg of shelled walnuts. Better, but still not good at all. This second try also resulted in me having a still now. I might make separate posts about that after I test its newest iteration – the first iteration was not very good at recovering the acetone from the solution (acetone is just too volatile) and after I modified it, I found out I don’t necessarily need it anymore.
Because the third try resulted in roughly 500 ml of oil from 1300 g of shelled walnuts after three hours of work and without the use of any chemicals and with minimum use of elektrimcity. And with walnut oil costing around 40€ per liter, that is financially viable since the next batch should be finished faster – I have a functioning process now and there won’t be any fumbling next time.
So, here goes the process:
- Drying the shelled walnuts at 45 °C in a fruit dehumidifier for 12 hours. This step is necessary now because the walnuts are freshly collected from the garden and when ground, they do not release oil but make a paste from which the oil is very difficult to extract. My first attempts at drying the nuts for a shorter time (2 h at 80°C or roasting 5 min at 190°C) did not work, thus me trying to extract the oil with acetone. I learned that the important thing is to get the walnuts completely dry, the shelled kernels should rustle when agitated.
- Running the dried walnuts through a meat grinder. This picture is from my first attempt but it is representative of how the shredded nuts looked after first grinding in my final attempt too. I am using an old hand-cranked meat grinder because I did not want to use my mom’s kitchen robot for experimentation. I probably won’t use it for this anyway, grinding the nuts is a bit harder than grinding meat and I fear the robot could get damaged. This old thing was made in times when tools were made to last and not break a month after the warranty expires.
- Running the dried walnuts through the meat grinder again. This time they started to expel some oil already.
- And finally, I run the thoroughly shredded kernels through another nearly antique kitchen appliance – a hand-cranked juicer. This resulted in 550 g of highly compressed dry matter with some oil residue, and the rest was oil mixed with some fine particles.
- Leaving the oil to settle out the particles. It will probably take a few days. I will skim the oil from the top in the meantime and add water for the particulate matter to drop into. I may use the still again to refine the oil further, using some chemicals again, but it can wait for later. For now, I just wait for it to settle. Here you can see how it settled after 24 hours.
I was not particularly careful about Hi Jean this time. The first 1000 ml of walnut oil (including oil from the first three experimental runs) will be refined and boiled for use as a food-safe wood finish and not for direct consumption. I do not have personal experience with walnut oil yet but allegedly it has advantages over linseed oil. It has a lower viscosity and thus seeps easier into the wood. It dries quicker. And it does not yellow with age as much as linseed oil does so it should not discolor the wood as much as linseed oil does, making it useful for lighter woods as well as dark ones. I intend to make several end-grain cutting boards at some point in the future.
However, I have cleaned all the appliances thoroughly now and next time I am making the oil, I will also make 1 l of cold-pressed oil – or maybe even more – for consumption. Walnut oil is a bit of a luxury foodstuff so we have no experience with its culinary use either but I am sure we will find some use for it in our kitchen should we have it. And an advantage of 1 l of oil is that it takes a lot less storage space than 5 kg of unshelled walnuts or 3 kg of shelled ones. Making it does not cost nearly as much as even cheap cooking oils do in financial terms, picking and drying the walnuts has to be done anyway, so there is only some work on top of that. And whilst it is not easy or quick work, I do have more time than money and I need the exercise anyway.