I can also suggest making tea. Use distilled water so you don't have to worry about impurities or pH. You can add a little lemon juice, maybe a teaspoon or two, but as I understand it, most of the mescaline is likely already in the malate salt form. Boil it for a a few hours, then leave it in the fridge for several hours or even for a couple days. Remove it from the fridge and carefully pour off as much of the clear liquid on top as possible pouring any of the solids. Repeat this process something like 4-6 times, collecting the resulting liquid. Note that you probably don't need more than an hour of boiling for the later extractions. The collected liquid will need to be reduced to some reasonable drinkable portion. Be mindful of heat applied in these processes. The plant matter mix may be prone to boiling over. Keep the heat especially low while reducing as the liquid thickens, which can cause the temperature to rise and increase the chance of damaging the alkaloids. Watch closely to avoid letting it get too hot or dry too quickly. For your 81g, if you can reduce it down to 160 mL, that's great, but that might be too thick and 250 mL may be more reasonable. You'll have to figure it out for your material.
Every cactus is different, and their strength can vary by many times. A very strong trip may require as little as 15g or more than 200 g. What I would do is start with 20g or one quarter of the preparation. It probably won't be that strong, but then you'll still have 60g left over for a stronger trip later. Only a handful of cacti are overpowering with only 20 g, and almost all active San Pedro do at least something at 60 g. For many 60 g is plenty strong.
I know a lot of people complain about the taste, but I think it's a bit exaggerated. Depending on the cactus and the presence of polyphenols and tannins and the like, it can be extremely bitter and also oddly salty, but it is medicine after all. IMO, the key is to avoid consuming the solids and to keep the drinkable portion small enough. Don't hesitate, allowing unpleasant flavors to linger. Just drink it. Have some water or other drink to chase with. Split the dose into two swigs, about 15-20 minutes apart, or if you can bear the flavor, sip it over a similar period. By not drinking it all at once, you reduce the likelihood of vagal reflex indued nausea which even pure mescaline can trigger sometimes.
I highly recommend taking it during the day, shortly after you wake up because it lasts a long time and I think it has more to offer in daylight than darkness. I also recommend spending much of the trip outside in a "natural" setting if possible. Keep in mind that it takes effect very slowly and will probably need at least 4 hours to peak. (I've had cacti that didn't peak until 7 hours in.) The whole experience lasts 10-14 hours or more for large doses. If you are used to mushrooms and LSD, you will probably find mescaline to be more lucid than those relative to the strength of effects. Some people find it more stimulating as well, but opinions vary as do different cacti.
Good luck!
