grist
/ɡrist/
noun
- grain or a batch of grain for grinding
- the product obtained from a grist of grain including the flour or meal and the grain offals
- a required or usual amount
- matter of interest or value forming the basis of a story or analysis
- something turned to advantage or use —used especially in the phrase grist for one's mill
grain
\ ˈgrān \
noun
- obsolete : a single small hard seed
- a seed or fruit of a cereal grass : CARYOPSIS
- the seeds or fruits of various food plants including the cereal grasses and in commercial and statutory usage other plants (such as the soybean)
- plants producing grain
...
Poppy grist is a weird description in general. While it is clear what is ment, it is synonymous with calling it poppy flour. Poppy grounds would probably be a better description.
The real problem is that opium is literally just the dried "sap" of the poppy flower. You harvest it from the bulbs while the plant is growing by gently cutting the bulb. If you were to grind up the bulbs, you need to filter out the fibers somehow.