The only time I ever got a good extraction was with very little basic water and shredded bark. I botched it every other time.
With ACRB (if that's what you're using), you get kind of oily stuff on account of the NMT which is an oil.
Good to use freezing as well since a lot of that NMT oil floats in freezing naphtha, and you can skim it off and give to your newbie friends or whatever since it's mostly NMT but has enough DMT as well. The good stuff stays suspended or snows to the bottom.
I couldn't say for sure if shredded is better but it's what I got this time. Shredded has good, low surface area but won't gunk up in solution like powder. It comes down to personal preference, I think.
For me, I would go shredded then cut it up even finer with scissors or some kind of grinding device, then even go so far as to freeze cycle it to break down cell walls. Acacia makes sticky goo that likes to sludge up in STB (which I also prefer).
Hell, get both and see which one gets a better yield ^_^
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