Well... the cannabis must be ground as fine as possible to help its absorption by the oil. As finer it is, as better.

And i think just mixing it with the oil, without heating, wouldnt work very well... heating is needed for increasing the speed the THC is dissolved.
For example: some people dissolve the weed in alcohol for making a tincture called green dragon. (BTW its also a very good way for ingesting cannabis). When they just let the weed soaking in it, without heating, it takes weeks to get an reasonable amount of THC dissolved in the alcohol. But heating it allows the tincture be made in only one hour.

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