Add the coffee beans to a slow cooker or crockpot.

Cover the coffee beans with olive oil.

Stir the mixture so that the coffee beans are coated with the oil. Turn on the crockpot (low heat for roasted beans, medium/high heat for un-roasted beans).

Stir the coffee beans every hour so that you don't burn them. The total time can be between 8 to 10 hours. 

If you are using green coffee beans, you may need to check them more often. Turn the crockpot setting to low when the green coffee beans turn brown. 

Now, keep a piece of cheesecloth on the mouth of the mason jar. Place a tea strainer on the cheesecloth to catch the coffee beans and any smaller impurities. 

Scoop out the coffee beans from the crockpot and put it in the tea strainer. Press the coffee beans with the back of a spoon to squeeze out the oil and then discard them. 

Pour the remaining oil from the crockpot into the cheesecloth.

Seal the mason jar and store in a cool, dark and dry place until you are ready to use it!