Ok check this out, I really find pleasure in experimenting with different methods of alkaloid extraction.Based on several factors ($$,time,chems,ect) I have been doing an A/B using distilled vinegar and DH2O in small enough amounts to fresh san pedro blended fresh and boiled past the snot green to the point where you can see the alkaloids have been absorbed into the acid/h20.
Then it's filtered an wrung out threw a t-shirt and the remaining green watery layer is boiled off to the point when another filter job gets all remaining plant debree. Once I've gotten the now clearish golden glob almost completely dry I add 250ml of ethenol or pure acetone and a white solid forms and is quickly filtered to continue with a now translucent golden syrup.

Question?
Whats the white precipitate?

Could be mesc and cacti alkaloids. Hope you didnt throw it out!

They are in their salt acetate form from the vinegar, suspended and partially dissolved in the syrup. Since salts are not very soluble in high proof ethanol or pure acetone, once the solution begins dissolving the syrup the salted alkaloids could crash out. You can know for sure by checking if the white precipitate dissolves in water. If it does, then it is likely mesc and alkaloids you want to keep. Could try crystallizing the white precip by dissolving in water and evaporating, if so desired.