Bho Filtering Question

Hello,
Canadian here, with a question about filtering plant matter from bho extraction. I have noticed that when I run food grade butane through any plant matter that has any fan leafs in it, then I get a black residue that comes off the material. I do not have this problem when I use high quality trim or bud. It only happens with lower quality material.
Currently I use 4 coffee filters to filter my bho before reducing it and vac purging.
Is there any way to filter the butane better so I do not get the black residue from the fan leafs?
 
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The residue is probably a high amount of waxes that are found in fan leaves. There is just a lot of fats and waxes that also dissolve into the butane. There is a freezing process that helps to remove the waxes, but I don't know the specifics. The extra waxes also can make it very crumbly,or very dark/gooey. At least this is my experience about it.
 
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